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2021
SNAPSHOT USA 2019: a coordinated national camera trap survey of the United States, ECOLOGY
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Authors: Cove, M, ....., Gerber, BD, Burr, J, et al.
https://doi.org/10.1002/ecy.3353 Abstract: With the accelerating pace of global change, it is imperative that we obtain rapid inventories of the status and distribution of wildlife for ecological inferences and conservation planning. To address this challenge, we launched the SNAPSHOT USA project, a collaborative survey of terrestrial wildlife populations using camera traps across the United States. For our first annual survey, we compiled data across all 50 states during a 14‐week period (17 August ‐ 24 November of 2019). We sampled wildlife at 1509 camera trap sites from 110 camera trap arrays covering 12 different ecoregions across four development zones. This effort resulted in 166,036 unique detections of 83 species of mammals and 17 species of birds. All images were processed through the Smithsonian’s eMammal camera trap data repository and included an expert review phase to ensure taxonomic accuracy of data, resulting in each picture being reviewed at least twice. The results represent a timely and standardized camera trap survey of the USA. All of the 2019 survey data are made available herein. We are currently repeating surveys in fall 2020, opening up the opportunity to other institutions and cooperators to expand coverage of all the urban‐wild gradients and ecophysiographic regions of the country. Future data will be available as the database is updated at eMammal.si.edu/snapshot‐usa, as well as future data paper submissions. These data will be useful for local and macroecological research including the examination of community assembly, effects of environmental and anthropogenic landscape variables, effects of fragmentation and extinction debt dynamics, as well as species‐specific population dynamics and conservation action plans. There are no copyright restrictions; please cite this paper when using the data for publication. |
Behavioral and demographic responses of mule deer to energy development on winter range. Wildlife Monograph.
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Authors: Northrup, JM, Anderson, C, Gerber, BD, and Wittemeyer, G. https://doi.org/10.1002/wmon.1060 SUMMARY OF CONCLUSIONS AND MANAGEMENT IMPLICATIONS Adult female mule deer showed substantial behavioral plasticity in the face of natural gas development, with no apparent demographic consequences. Topographically diverse winter range with adequate vegetation providing sufficient food and cover allow deer to alter behavior in an adaptive manner, and similar features should be considered in future development planning. |
Abstract: Anthropogenic habitat modification is a major driver of global biodiversity loss. In North America, one of the primary sources of habitat modification over the last 2 decades has been exploration for and production of oil and natural gas (hydrocarbon development), which has led to demographic and behavioral impacts to numerous wildlife species. Developing effective measures to mitigate these impacts has become a critical task for wildlife managers and conservation practitioners. However, this task has been hindered by the difficulties involved in identifying and isolating factors driving population responses. Current research on responses of wildlife to development predominantly quantifies behavior, but it is not always clear how these responses scale to demography and population dynamics. Concomitant assessments of behavior and population‐level processes are needed to gain the mechanistic understanding required to develop effective mitigation approaches. We simultaneously assessed the demographic and behavioral responses of a mule deer population to natural gas development on winter range in the Piceance Basin of Colorado, USA, from 2008 to 2015. Notably, this was the period when development declined from high levels of active drilling to only production phase activity (i.e., no drilling). We focused our data collection on 2 contiguous mule deer winter range study areas that experienced starkly different levels of hydrocarbon development within the Piceance Basin.
We assessed mule deer behavioral responses to a range of development features with varying levels of associated human activity by examining habitat selection patterns of nearly 400 individual adult female mule deer. Concurrently, we assessed the demographic and physiological effects of natural gas development by comparing annual adult female and overwinter fawn (6‐month‐old animals) survival, December fawn mass, adult female late and early winter body fat, age, pregnancy rates, fetal counts, and lactation rates in December between the 2 study areas. Strong differences in habitat selection between the 2 study areas were apparent. Deer in the less‐developed study area avoided development during the day and night, and selected habitat presumed to be used for foraging. Deer in the heavily developed study area selected habitat presumed to be used for thermal and security cover to a greater degree. Deer faced with higher densities of development avoided areas with more well pads during the day and responded neutrally or selected for these areas at night. Deer in both study areas showed a strong reduction in use of areas around well pads that were being drilled, which is the phase of energy development associated with the greatest amount of human presence, vehicle traffic, noise, and artificial light. Despite divergent habitat selection patterns, we found no effects of development on individual condition or reproduction and found no differences in any of the physiological or vital rate parameters measured at the population level. However, deer density and annual increases in density were higher in the low‐development area. Thus, the recorded behavioral alterations did not appear to be associated with demographic or physiological costs measured at the individual level, possibly because populations are below winter range carrying capacity. Differences in population density between the 2 areas may be a result of a population decline prior to our study (when development was initiated) or area‐specific differences in habitat quality, juvenile dispersal, or neonatal or juvenile survival; however, we lack the required data to contrast evidence for these mechanisms.
Given our results, it appears that deer can adjust to relatively high densities of well pads in the production phase (the period with markedly lower human activity on the landscape), provided there is sufficient vegetative and topographic cover afforded to them and populations are below carrying capacity. The strong reaction to wells in the drilling phase of development suggests mitigation efforts should focus on this activity and stage of development. Many of the wells in this area were directionally drilled from multiple‐well pads, leading to a reduced footprint of disturbance, but were still related to strong behavioral responses. Our results also indicate the likely value of mitigation efforts focusing on reducing human activity (i.e., vehicle traffic, light, and noise). In combination, these findings indicate that attention should be paid to the spatial configuration of the final development footprint to ensure adequate cover. In our study system, minimizing the road network through landscape‐level development planning would be valuable (i.e., exploring a maximum road density criteria). Lastly, our study highlights the importance of concomitant assessments of behavior and demography to provide a comprehensive understanding of how wildlife respond to habitat modification.
We assessed mule deer behavioral responses to a range of development features with varying levels of associated human activity by examining habitat selection patterns of nearly 400 individual adult female mule deer. Concurrently, we assessed the demographic and physiological effects of natural gas development by comparing annual adult female and overwinter fawn (6‐month‐old animals) survival, December fawn mass, adult female late and early winter body fat, age, pregnancy rates, fetal counts, and lactation rates in December between the 2 study areas. Strong differences in habitat selection between the 2 study areas were apparent. Deer in the less‐developed study area avoided development during the day and night, and selected habitat presumed to be used for foraging. Deer in the heavily developed study area selected habitat presumed to be used for thermal and security cover to a greater degree. Deer faced with higher densities of development avoided areas with more well pads during the day and responded neutrally or selected for these areas at night. Deer in both study areas showed a strong reduction in use of areas around well pads that were being drilled, which is the phase of energy development associated with the greatest amount of human presence, vehicle traffic, noise, and artificial light. Despite divergent habitat selection patterns, we found no effects of development on individual condition or reproduction and found no differences in any of the physiological or vital rate parameters measured at the population level. However, deer density and annual increases in density were higher in the low‐development area. Thus, the recorded behavioral alterations did not appear to be associated with demographic or physiological costs measured at the individual level, possibly because populations are below winter range carrying capacity. Differences in population density between the 2 areas may be a result of a population decline prior to our study (when development was initiated) or area‐specific differences in habitat quality, juvenile dispersal, or neonatal or juvenile survival; however, we lack the required data to contrast evidence for these mechanisms.
Given our results, it appears that deer can adjust to relatively high densities of well pads in the production phase (the period with markedly lower human activity on the landscape), provided there is sufficient vegetative and topographic cover afforded to them and populations are below carrying capacity. The strong reaction to wells in the drilling phase of development suggests mitigation efforts should focus on this activity and stage of development. Many of the wells in this area were directionally drilled from multiple‐well pads, leading to a reduced footprint of disturbance, but were still related to strong behavioral responses. Our results also indicate the likely value of mitigation efforts focusing on reducing human activity (i.e., vehicle traffic, light, and noise). In combination, these findings indicate that attention should be paid to the spatial configuration of the final development footprint to ensure adequate cover. In our study system, minimizing the road network through landscape‐level development planning would be valuable (i.e., exploring a maximum road density criteria). Lastly, our study highlights the importance of concomitant assessments of behavior and demography to provide a comprehensive understanding of how wildlife respond to habitat modification.
A synthesis of life-history, functional traits, and consequences of anthropogenic pressures on Madagascars threatened carnivorans, Eupleridae. Mammal Review.
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Authors: Wampole, EM, Farris, ZJ, and Geber, BD.
https://doi.org/10.1111/mam.12234 Abstract:
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Sex-segregated range use by black-and white ruFFed lemurs (Varecia variegata) in Ranomafana National Park, Madagascar. Folia Primatologica
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Authors: Baden, A, Oliveras, J, and Gerber, BD.
https://doi.org/10.1101/2020.03.30.016774 Abstract: Ranging behavior is one important strategy by which nonhuman primates obtain access to resources critical to their biological maintenance and reproductive success. As most primates live in permanent social groups, their members must balance the benefits of group living with the costs of intragroup competition for resources. However, some taxa live in more spatiotemporally flexible social groups, whose members modify patterns of association and range use as a method to mitigate these costs. Here, we describe the range use of one such taxon, the black-and-white ruffed lemur (Varecia variegata), at an undisturbed primary rain forest site in Ranomafana National Park, Madagascar, and characterize sex differences in annual home range area, overlap, and daily distances traveled. Moreover, we characterize seasonal variability in range use and ask whether ranging behaviors can be explained by either climatic or reproductive seasonality. We found that females used significantly larger home ranges than males, though sexes shared equal and moderate levels of home range overlap. Overall, range use did not vary across seasons, although within sexes, male range use varied significantly with climate. Moreover, daily path length was best predicted by day length, female reproductive state, and sex, but was unrelated to climate variables. While the patterns of range use and spatial association presented here share some similarities with “bisexually bonded” community models described for chimpanzees, we argue that ruffed lemurs best conform to a “nuclear neighborhood” community model wherein nuclear (core) groups share the highest levels of home range overlap, and where these groups cluster spatially into adjacent “neighborhoods” within the larger, communally defended territory. |
2020
Squeezed by a habitat split: Warm ocean conditions and old‐forest loss interact to reduce long‐term occupancy of a threatened seabird. Conservation Letters
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Authors: Betts, MG, Northrup, JM, Bailey Guerrero, JA, Adrean, LJ, Nelson, SK, Fisher, JL, Gerber, BD, Garcia-Heras, MS, Yang, Z, Roby, DD, and Rivers, J.
https://doi.org/10.1111/conl.12745 Abstract Theory predicts that species requiring multiple habitat types simultaneously should have heightened sensitivity to anthropogenic pressures, yet tests of this prediction are especially rare. We tested whether breeding site occupancy of the threatened marbled murrelet (Brachyramphus marmoratus) was driven by the synergistic effects of nesting habitat loss in forests, and changing ocean conditions. We paired 70,700 murrelet surveys at 19,837 sites across 20 years from the Oregon Coast Range with annual data on the extent of old forest and biophysical ocean conditions. Dynamic occupancy models indicated that local murrelet colonization rates were strongly reduced during warm ocean conditions with low prey availability. Landscapes that contained more old forest and were closer to the ocean showed reduced rates of local extinction. Given predictions of accelerated ocean warming and increased global timber demand, our results suggest murrelets may continue to be imperiled by deterioration of the two habitats upon which they depend. |
Assessment of the threatened carnivore community in the recently expanded rainforest protected area Anjanaharibe-Sud Special Reserve, Madagascar. Endangered Species Research.
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Authors: Ross, P, Patel, E, Ferguson, B, Ravelijaona, R, Raoloniana, G, Wampole, E*, Gerber, BD, and Farris, Z.
DOI: https://doi.org/10.3354/esr01055 Abstract: Madagascar is an island nation renowned for its biodiversity and species endemism, yet it is still largely understudied despite intense anthropogenic threats including forest loss and edge effects. Anjanaharibe-Sud Special Reserve is a recently expanded rainforest protected area that is lacking detailed surveys and assessments of the native carnivore community of the endemic family Eupleridae. To identify which terrestrial carnivores occupy the reserve and what anthropogenic disturbances and factors best explain their occurrence patterns, we deployed 35 motion-activated cameras to detect native and introduced carnivores. From November 2018 to February 2019, we collected 2918 unique capture events (all species) and confirmed the presence of 5 euplerids: Galidia elegans, Galidictis fasciata, Eupleres goudotii, Fossa fossana, and Cryptoprocta ferox. These results extend the known range of E. goudotii and G. fasciata. In the reserve, F. fossana and G. elegans were the most common and widespread native carnivores, while E. goudotii was the rarest. We highlight the negative impact of edge effects on G. fasciata and F. fossana and the threat posed by the free-ranging non-native carnivore C. familiaris. This study represents the first detailed survey and occurrence estimates of the carnivore community of this protected area, allowing comparison with other protected areas in Madagascar. Our empirical findings show that anthropogenic disturbance negatively impacts carnivore existence within the Anjanaharibe-Sud Special Reserve and provide important management recommendations for protecting the carnivore community and the co-occurring wildlife living within this area. |
Contrasting eFFects of climate change on seasonal survival of a seasonally active mammal.
Proceedings of the National Academy of Science.
Proceedings of the National Academy of Science.
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Authors: Cordes, L, Blumstein, DT, Armitage, KB, CaraDonna, PJ, Childs, DZ, Gerber, BD, Marten, JGA, Oli, MK, and Ozgul, A.
https://doi.org/10.1073/pnas.1918584117 Abstract: Seasonal environmental conditions shape the behavior and life history of virtually all organisms. Climate change is modifying these seasonal environmental conditions, which threatens to disrupt population dynamics. It is conceivable that climatic changes may be beneficial in one season but result in detrimental conditions in another because life-history strategies vary between these time periods. We analyzed the temporal trends in seasonal survival of yellow-bellied marmots (Marmota flaviventer) and explored the environmental drivers using a 40-y dataset from the Colorado Rocky Mountains (USA). Trends in survival revealed divergent seasonal patterns, which were similar across age-classes. Marmot survival declined during winter but generally increased during summer. Interestingly, different environmental factors appeared to drive survival trends across age-classes. Winter survival was largely driven by conditions during the preceding summer and the effect of continued climate change was likely to be mainly negative, whereas the likely outcome of continued climate change on summer survival was generally positive. This study illustrates that seasonal demographic responses need disentangling to accurately forecast the impacts of climate change on animal population dynamics. |
Exploring and interpreting spatiotemporal interactions among native invasivecarnivores across a gradient of rai nforest degradation. Biological Invasions.
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Authors: Farris, ZJ, Gerber, BD Karpanty, S, Murphy, A, Wampole, EM, Ratelolahy, F, and Kelly, M.
https://link.springer.com/article/10.1007/s10530-020-02237-1 Abstract: Studies of elusive carnivores often rely on passive sampling when investigating either spatial or temporal interactions. However, inference on behavioral mechanisms are usually lacking. We present an analysis that combines previously published spatial co-occurrence estimates and temporal kernel density estimates to explore spatiotemporal interspecific interactions. We do so by deriving a spatiotemporal value (STV) that is a relative measure of potential interaction in both niche dimensions, across a gradient of degradation, for rainforest carnivore pairs in Madagascar. We also use a conceptual framework to provide insight into the potential behavioral mechanisms of habitat selection. Of the six native and three invasive carnivores, we estimate the spatiotemporal interactions for twelve pairings, which range from no spatial/temporal relationship (n = 5) to spatiotemporal aggregation or segregation (n = 7). We visualized these spatiotemporal interactions along a fragmentation gradient and demonstrate that these interactions are not static, as STV overlap increases with increasing anthropogenic disturbance. Of the three invasive carnivores (free-ranging dogs Canis familiaris, cats Felis species, and small Indian civets Viverricula indica) the latter had the highest number of spatial occurrence (n = 4) and spatiotemporal overlap (n = 4) relationships with native carnivores. Our results highlight the potential for increasing direct and indirect interactions between native and invasive species as forest degradation and invasive predators increase. Our approach allows us to better understand adaptive behaviors, plasticity in temporal activity, community assemblage, and to develop targeted conservation strategies to manage ecological communities in rapidly changing ecosystems. |
Improving spatial predictions of animal resource selection to guide conservation decision making. Ecology.
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Authors: Gerber, BD and Northrup, JM
https://doi.org/10.1002/ecy.2953 Abstract: Resource selection is often studied by ecologists interested in the environmental drivers of animal space use and movement. These studies commonly produce spatial predictions, which are of considerable utility to resource managers making habitat and population management decisions. It is thus paramount that predictions from resource selection studies are accurate. We evaluated model building and fitting strategies for optimizing resource selection function predictions in a use‐availability framework. We did so by simulating low‐ and high‐intensity spatial sampling data that respectively predicted study area and movement‐based resource selection. We compared one of the most commonly used forms of statistical regularization, Akaike's Information Criterion (AIC), with the lesser used least absolute shrinkage and selection operator (LASSO). LASSO predictions were less variable and more accurate than AIC and were often best when considering additive and interacting variables. We explicitly demonstrate the predictive equivalence using the logistic and Poisson likelihoods and how it is lost when the available sample is too small. Regardless of modeling approach, interpreting the sign of coefficients as a measure of selection can be misleading when optimizing for prediction. |
Power pole density and avian electrocution risk throughout the western United States. Journal of Raptor Research.
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Authors: Dwyer, JF, Gerber, BD, Petersen, P, Armstrong, WE, & Harness, R.
https://doi.org/10.3356/0892-1016-54.2.93 Abstract: Avian electrocutions on power poles affect raptor populations globally. Mitigation strategies in the USA are typically bottom-up, combining risk assessments for individual poles into a utility-specific avian protection plan. This approach is usually reactive, relying on incidental documentation of electrocutions for initiation, and can allow uncoordinated mitigation strategies among adjacent utilities. A top-down strategy may help solve both problems if maps identifying where distribution power poles occur were available for comparison to range maps for species at risk of electrocution. Range maps exist but pole location data are rarely publicly available in the USA. Pole-density models were previously created for Colorado and Wyoming, the Great Basin, and the Columbia Plateau because pole density can serve as a surrogate for electrocution risk. We used each of these models to predict pole densities throughout four additional areas: the Northwestern Plains, Southwestern Plains, Southwestern Plateaus, and parts of New Mexico not included in other modeled areas. We also applied the Colorado and Wyoming model to portions of the Uinta Basin and Wyoming Basin projecting from Colorado and Wyoming into Idaho and Utah. The Colorado and Wyoming model fit all areas better than other models, except parts of New Mexico not included in other modeled areas, where the Great Basin model fit best. Our model predictions facilitate assessment of pole density across much (2,573,746 km2) of the western USA. To assess whether the models are useful in predicting electrocutions, we compared predicted pole densities throughout White Sands Missile Range to locations of 59 avian electrocutions. Electrocutions occurred at low rates in cells with low predicted pole densities, and at higher rates in cells with moderate and high predicted pole densities. Because the models do not include species-specific information, they have the potential to be applicable to the conservation of a wide variety of species. |
2019
extreme site FIdelity as an optimal strategy in an unpredictable and homogeneous environment.
Functional Ecology
Functional Ecology
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Authors: Gerber, BD, Hooten, MB, Peck, CP, Rice, MB, Gammonley, JH, Apa, AD, and Davis, AJ.
https://doi.org/10.1111/1365-2435.13390 Abstract:
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2018
Elevated potential for intraspeciFIc competition in small tiger populations occupying fragmented landscapes. Biological Conservation.
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Authors: Chanchani, P, Gerber, BD, Noon, B.
https://doi.org/10.1016/j.biocon.2018.08.017 Abstract: The distribution of mammals is determined by a suite of endogenous and exogenous factors. In territorial, polygynous species like tigers (Panthera tigris), males often center their space-use around female territories, repelling competitors from these areas. Competition among males for females leads to increased mortality of both sexes and infanticide of unrelated cubs, which can lead to population declines. We hypothesized that increased territorial overlap among adult male tigers and elevated levels of inter and intra-sex competition would be manifest in populations with male-biased adult sex ratios (ASR). We also assessed whether inter-sex variation in adult survival or degree of habitat connectivity resulted in skewed ASR. We evaluated these hypotheses using camera trap data from three tiger populations occupying habitat patches with varying levels of connectivity and ASRs. Data were analyzed using multi-state occupancy models, where states were defined as habitat use by one or more male tigers in sites with and without female use. As predicted, in populations with male-biased or even ASR we found evidence for increased spatial overlap between male tigers, particularly pronounced in areas adjacent to female territories. Given parity in adult survival, habitat fragmentation likely caused male-biased ASR. Our results suggest that the persistence of small tiger populations in habitat patches with male-biased ASR may be significantly compromised by behavior-mediated endogenous demographic processes that are often overlooked. In habitat fragments with pronounced male biased ASR, population recovery of territorial carnivores may require timely supplementation of individuals to compensate for population losses from intraspecific competition. |
Accounting for location uncertainty in azimuthal telemetry data improves
ecological inference. Movement Ecology.
ecological inference. Movement Ecology.
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Authors: Gerber, BD, Hooten, MB, Peck, CP, Rice, MB, Gammonley, JH, Apa, AD, and Davis, AJ
Abstract:Characterizing animal space use is critical for understanding ecological relationships. Animal telemetry technology has revolutionized the fields of ecology and conservation biology by providing high quality spatial data on animal movement. Radio-telemetry with very high frequency (VHF) radio signals continues to be a useful technology because of its low cost, miniaturization, and low battery requirements. Despite a number of statistical developments synthetically integrating animal location estimation and uncertainty with spatial process models using satellite telemetry data, we are unaware of similar developments for azimuthal telemetry data. As such, there are few statistical options to handle these unique data and no synthetic framework for modeling animal location uncertainty and accounting for it in ecological models. We developed a hierarchical modeling framework to provide robust animal location estimates from one or more intersecting or non-intersecting azimuths. We used our azimuthal telemetry model (ATM) to account for azimuthal uncertainty with covariates and propagate location uncertainty into spatial ecological models. We evaluate the ATM with commonly used estimators (Lenth (1981) maximum likelihood and M-Estimators) using simulation. We also provide illustrative empirical examples, demonstrating the impact of ignoring location uncertainty within home range and resource selection analyses. We further use simulation to better understand the relationship among location uncertainty, spatial covariate autocorrelation, and resource selection inference. |
Transboundary cooperation improves endangered species monitoring and conservation actions: a case study of the global population of Amur leopards. Conservation Letters.
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Authors: ]. Vitkalova, AV, Feng, L, Rybin, AN, Gerber, BD, Miquelle, DG, Wang, T, Yang, H, Shevtsova, EI, Vladimir, Aramilev, V, Ge, J.
https://doi.org/10.1111/conl.12574 Abstract: Political borders and natural boundaries of wildlife populations seldom coincide, often to the detriment of conservation objectives. Transnational monitoring of endangered carnivores is rare, but is necessary for accurate population monitoring and coordinated conservation policies. We investigate the benefits of collaboratively monitoring the abundance and survival of the critically endangered Amur leopard, which occurs as a single transboundary population across China and Russia. Country-specific results overestimated abundance and were generally less precise compared to integrated monitoring estimates; the global population was similar in both years: 84 (70–108, 95% confidence interval). Uncertainty in country-specific annual survival estimates were approximately twice the integrated estimates of 0.82 (0.69–0.91, 95% confidence limits). This collaborative effort provided a better understanding of Amur leopard population dynamics, represented a first step in building trust, and lead to cooperative agreements to coordinate conservation policies. |
Adaptive management of animal populations with signiFicant unknowns and uncertainties: a case study. Ecological Applications.
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Authors: Gerber, BD and Kendall, WD
https://doi.org/10.1002/eap.1734 Abstract: Conservation and management decision making in natural resources is challenging due to numerous uncertainties and unknowns, especially relating to understanding system dynamics. Adaptive resource management (ARM) is a formal process to making logical and transparent recurrent decisions when there are uncertainties about system dynamics. Despite wide recognition and calls for implementing adaptive natural resource management, applications remain limited. More common is a reactive approach to decision making, which ignores future system dynamics. This contrasts with ARM, which anticipates future dynamics of ecological process and management actions using a model‐based framework. Practitioners may be reluctant to adopt ARM because of the dearth of comparative evaluations between ARM and more common approaches to making decisions. We compared the probability of meeting management objectives when managing a population under both types of decision frameworks, specifically in relation to typical uncertainties and unknowns. We use a population of Sandhill Cranes as our case study. We evaluate each decision process under varying levels of monitoring and ecological uncertainty, where the true underlying population dynamics followed a stochastic age‐structured population model with environmentally driven vital rate density dependence. We found that the ARM framework outperformed the currently employed reactive decision framework to manage Sandhill Cranes in meeting the population objective across an array of scenarios. This was even the case when the candidate set of population models contained only naïve representations of the true population process. Under the reactive decision framework, we found little improvement in meeting the population objective even if monitoring uncertainty was eliminated. In contrast, if the population was monitored without error within the ARM framework, the population objective was always maintained, regardless of the population models considered. Contrary to expectation, we found that age‐specific optimal harvest decisions are not always necessary to meet a population objective when population dynamics are age structured. Population managers can decrease risks and gain transparency and flexibility in management by adopting an ARM framework. If population monitoring data has high sampling variation and/or limited empirical knowledge is available for constructing mechanistic population models, ARM model sets should consider a range of mechanistic, descriptive, and predictive model types. |
Making the most of sparse data to estimate density of a rare and threatened species:
a case study with the fosa, a little-studied Malagasy carnivore. Animal Conservation.
a case study with the fosa, a little-studied Malagasy carnivore. Animal Conservation.
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Authors: Murphy, A*, Gerber, BD, Kelly, MJ, Karpanty, S, Ratelohy, F, Farris, Z.
https://doi.org/10.1111/acv.12420 Abstract: Sparse detections in camera trap surveys commonly hinder density estimation for threatened species. By combining detections across multiple surveys, or using informative priors in Bayesian model fitting, researchers can improve parameter estimation from sparse capture–recapture data. Using a spatial mark–resight model that incorporates site‐level heterogeneity in the spatial scale parameter via a hierarchical process and prior information, we estimated the density of a threatened carnivore (fosa, Cryptoprocta ferox) from multiple sparse datasets collected during extensive camera trapping surveys in northeastern Madagascar (2008–2015). Our objectives were to estimate density for six sites, examine the response of fosa density and movement to habitat degradation, monitor annual density trends across 7 years at two sites, and estimate fosa abundance in the Makira–Masoala protected area complex. We obtained a mean of 16.1 (se = 0.52; range = 2–49) fosa detections and three observers identified a mean of 3.62 (se = 0.09; range = 1–8) marked individuals per survey. Fosa daily baseline encounter rate was very low (λ0 = 0.004; 0.003–0.006) and density/movement estimates were similar across forest types. Density estimates at resurveyed sites suggested annual variability in density, with estimates trending lower during the final surveys [e.g. D = 0.39 (0.14–1.11) versus 0.08 (0.05–0.31) individuals per km2]. We estimated fosa abundance across the Makira–Masoala region to be 1061 (95% HPDI: 596–1780) adult individuals. On the basis of our estimate and the size of the region, we believe Makira–Masoala harbors a significant portion of the global fosa population. The conservation and management of rare species is commonly limited due to lack of population estimates. By combining detections across surveys, we overcame estimation issues and obtained valuable information on a threatened carnivore, allowing us to better assess its status and prioritize conservation actions. We advocate for practical use of sparse datasets for such data‐deficient species. |
A comment on Bayesian occupancy priors. Plos One.
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Authors: Northrup, J and Gerber, BD.
https://doi.org/10.1371/journal.pone.0192819 Abstract: Understanding patterns of species occurrence and the processes underlying these patterns is fundamental to the study of ecology. One of the more commonly used approaches to investigate species occurrence patterns is occupancy modeling, which can account for imperfect detection of a species during surveys. In recent years, there has been a proliferation of Bayesian modeling in ecology, which includes fitting Bayesian occupancy models. The Bayesian framework is appealing to ecologists for many reasons, including the ability to incorporate prior information through the specification of prior distributions on parameters. While ecologists almost exclusively intend to choose priors so that they are “uninformative” or “vague”, such priors can easily be unintentionally highly informative. Here we report on how the specification of a “vague” normally distributed (i.e., Gaussian) prior on coefficients in Bayesian occupancy models can unintentionally influence parameter estimation. Using both simulated data and empirical examples, we illustrate how this issue likely compromises inference about species-habitat relationships. While the extent to which these informative priors influence inference depends on the data set, researchers fitting Bayesian occupancy models should conduct sensitivity analyses to ensure intended inference, or employ less commonly used priors that are less informative (e.g., logistic or t prior distributions). We provide suggestions for addressing this issue in occupancy studies, and an online tool for exploring this issue under different contexts. |
2017
Identifying Species conservation strategies to reduce disease-associated declines. Conservation Letters.
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Authors: Gerber, BD, Converse, SJ, Crockett, H, Muths, E, Mosher, B*, and Bailey, L.
https://doi.org/10.1111/conl.12393 Abstract: Emerging infectious diseases (EIDs) are a salient threat to many animal taxa, causing local and global extinctions, altering communities and ecosystem function. The EID chytridiomycosis is a prominent driver of amphibian declines, which is caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd). To guide conservation policy, we developed a predictive decision‐analytic model that combines empirical knowledge of host‐pathogen metapopulation dynamics with expert judgment regarding effects of management actions, to select from potential conservation strategies. We apply our approach to a boreal toad (Anaxyrus boreas boreas) and Bd system, identifying optimal strategies that balance tradeoffs in maximizing toad population persistence and landscape‐level distribution, while considering costs. The most robust strategy is expected to reduce the decline of toad breeding sites from 53% to 21% over 50 years. Our findings are incorporated into management policy to guide conservation planning. Our online modeling application provides a template for managers of other systems challenged by EIDs. |
A biogeographical perspective on the variation in mouse lemur density across Madagascar. Mammal Review.
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Authors: Setash, C*, Zohdy, S, Gerber, BD, and Karanewsky, C
https://doi.org/10.1111/mam.12093 Abstract:
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Preventing global extinction of the Javan rhino: tsunami risk and future conservation direction. Conservation Letters.
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Authors: Setiawan, R, Gerber, BD, Rahmat, UM, Daryan, D, Firdaus, AY, Haryono, M, Khairani, KO, Kurniawan, Y, Long, B, Lyet, A, Muhiban, M, Mahmud, R, Muhtarom, A, Purastuti, E, Ramono, WS, Subrata, D, Sunarto, S.
https://doi.org/10.1111/conl.12366 Abstract: The Javan rhino (Rhinoceros sondaicus) is one of the most threatened mammals on Earth. The only remaining individuals live as part of a small population isolated in a single protected area, Ujung Kulon National Park, Java, Indonesia. Despite almost a century of studies, little is known about the factors that affect Javan rhino demography and distribution. National park officials require such information to identify conservation strategies and track the success and failures of these efforts; translocating selected individuals to establish a second population has been considered, but the risks must be weighed. We show that the 2013 global population of Javan rhinos was 62 individuals, which is likely near the site's carrying capacity. Our analysis of rhino distribution indicates that tsunamis are a significant risk to the species in Ujung Kulon, justifying the risks of establishing additional populations. Continued individual‐based monitoring is needed to guide future translocation decisions. |
EFFects of El Nino on the population dynamics of the Malay civet east of the Wallace line. Journal of Zoology.
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Authors: Seymour, AS, Tarrant, MR, Gerber, BD, Sharp, A, Woollam J, and Cox, R.
https://doi.org/10.1111/jzo.12469 Abstract: The effect of climate on the population dynamics of rainforest vertebrates is known only for a limited subset of species and study locations. To extend this knowledge, we carried out an 8‐year population study of a Viverrid (Malay civet Viverra tangalunga) in the Wallacea biogeographical region (Buton Island, Sulawesi). Civets were trapped annually from 2003 to 2010, during which there were four weak to moderate El Niño events and one moderate La Niña event. In Indonesia, El Niño events are associated with drier than normal conditions, while La Niña is associated with wetter conditions. The number of individuals captured was strongly correlated with the 12‐month summed Southern Oscillation Index (SOI) prior to trapping, with significantly fewer individuals caught in years with lower summed SOI (i.e. stronger El Niño conditions). Adult civet body mass was significantly higher in El Niño years; mean adult male and female body masses were 10.6% and 4.0% greater in El Niño years. There was support for a 1‐year time lagged effect of El Niño on the apparent survival (1 – probability of disappearing from the study site due to death or emigration) of male (but not female) civets, which was approximately 50% higher in the year following El Niño events. Using spatially explicit capture–mark–recapture models, we were unable to detect any significant change in civet density between years, which was estimated as 1.36 ± 0.14 (se) individuals km−2. We suggest that increased apparent survival of males observed in the year after El Niño events was brought about by reduced dispersal (possibly associated with a change in mating tactic) rather than reduced mortality. |
Threats to a rainforest carnivore community: a multi-year assessment of occupancy and cooccurrence
in Madagascar. Biological Conservation.
in Madagascar. Biological Conservation.
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Authors: Farris, ZJ, Gerber, BD, Valenta, K, Rafaliarison, R, Raza mahaimodison, JC, Larney, E, Hariniaina, T, Randriana, Z, Wright, PC, and Chapman, CA.
https://doi.org/10.1016/j.biocon.2017.04.010 Abstract: Protected areas (PA) aim to eliminate many of the threats that species face on the greater landscape. In the last three decades, PA's have expanded considerably; however, quantitative assessments of how well they have mitigated threats to habitat and biodiversity are very limited. Habitat bordering PA's and the wildlife that use it are threatened by a wide-range of anthropogenic pressures (e.g., edge effects, fragmentation, and introduced predators) and this situation is particularly acute for low-density, poorly studied carnivore communities. From 2010 to 2015, we photographically sampled within (contiguous forest) and bordering (degraded, fragmented forest) a UNESCO World Heritage rainforest PA in Madagascar - Ranomafana National Park (RNP). We investigated the effects of invasive predators, local people presence, and habitat quality on the endemic rainforest carnivore community using static, dynamic, and co-occurrence models. We found native carnivores to be absent or have a low probability of occurrence in degraded forest bordering the PA, while local people and dogs (Canis familiaris) had high occurrence. Madagascar's largest endemic carnivore, the fosa (Cryptoprocta ferox) and the much smaller ring-tailed vontsira (Galidia elegans), occurrence in RNP declined rapidly over six years; their strong co-occurrence with dogs suggests interspecific competition, direct aggression/mortality, or disease as the cause. We highlight the dangers posed to biodiversity, particularly carnivores, from anthropogenic pressures bordering PA's and present recommendations to address increased human and dog activity, including programs to control dogs and their impact on biodiversity. |
Evaluating and improving count-based population inference: A case study from 31 years of monitoring sandhill cranes. Condor: Ornithological Applications.
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Authors: Gerber, BD and Kendall, WL.
https://doi.org/10.1650/CONDOR-16-137.1 Abstract: Monitoring animal populations can be difficult. Limited resources often force monitoring programs to rely on unadjusted or smoothed counts as an index of abundance. Smoothing counts is commonly done using a moving-average estimator to dampen sampling variation. These indices are commonly used to inform management decisions, although their reliability is often unknown. We outline a process to evaluate the biological plausibility of annual changes in population counts and indices from a typical monitoring scenario and compare results with a hierarchical Bayesian time series (HBTS) model. We evaluated spring and fall counts, fall indices, and model-based predictions for the Rocky Mountain population (RMP) of Sandhill Cranes (Antigone canadensis) by integrating juvenile recruitment, harvest, and survival into a stochastic stage-based population model. We used simulation to evaluate population indices from the HBTS model and the commonly used 3-yr moving average estimator. We found counts of the RMP to exhibit biologically unrealistic annual change, while the fall population index was largely biologically realistic. HBTS model predictions suggested that the RMP changed little over 31 yr of monitoring, but the pattern depended on assumptions about the observational process. The HBTS model fall population predictions were biologically plausible if observed crane harvest mortality was compensatory up to natural mortality, as empirical evidence suggests. Simulations indicated that the predicted mean of the HBTS model was generally a more reliable estimate of the true population than population indices derived using a moving 3-yr average estimator. Practitioners could gain considerable advantages from modeling population counts using a hierarchical Bayesian autoregressive approach. Advantages would include: (1) obtaining measures of uncertainty; (2) incorporating direct knowledge of the observational and population processes; (3) accommodating missing years of data; and (4) forecasting population size. |
A model to inform management actions as a response to Chytridiomycosis-Associated Decline. EcoHealth.
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Authors: Converse, SJ, Bailey, LL, Mosher*, B, Funk, C, Gerber, BD, and Muths, E.
http://doi.org/10.1007/s10393-016-1117-9 Abstract: Decision-analytic models provide forecasts of how systems of interest will respond to management. These models can be parameterized using empirical data, but sometimes require information elicited from experts. When evaluating the effects of disease in species translocation programs, expert judgment is likely to play a role because complete empirical information will rarely be available. We illustrate development of a decision-analytic model built to inform decision-making regarding translocations and other management actions for the boreal toad (Anaxyrus boreas boreas), a species with declines linked to chytridiomycosis caused by Batrachochytrium dendrobatidis (Bd). Using the model, we explored the management implications of major uncertainties in this system, including whether there is a genetic basis for resistance to pathogenic infection by Bd, how translocation can best be implemented, and the effectiveness of efforts to reduce the spread of Bd. Our modeling exercise suggested that while selection for resistance to pathogenic infection by Bd could increase numbers of sites occupied by toads, and translocations could increase the rate of toad recovery, efforts to reduce the spread of Bd may have little effect. We emphasize the need to continue developing and parameterizing models necessary to assess management actions for combating chytridiomycosis-associated declines. |
2016
Modeling co-occurrence between toxic prey and naTive predators in an incipient invasion. Biodiversity and Conservation
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Authors: Brown, KA, Farris, ZJ, Yesuf, G, Gerber, BD, Rasambainarivo, D, Karpanty, S, Kelly, MJ, Raza mahaimodison, JC, Larney, E, Wright, P, and Johnson, SE.
http://doi.org/10.1007/s10531-016-1198-3 Abstract: Biological invasions can represent important threats to endemic species, including those within the invaders’ food webs. The Asian common toad (Duttaphrynus melanostictus) was introduced to Madagascar in 2011. This introduction presents a potentially dangerous prey item to a relatively naïve, highly diverse endemic carnivore fauna. Using a multivariate niche modeling approach (background test), we assessed the predicted niche overlap between D. melanostictus and six endemic carnivores in eastern Madagascar. The overlap between this potential prey and predators was assessed on four environmental niche axes: temperature, precipitation, vegetation cover and elevation. Our results showed a mixture of niche overlap and divergence between D. melanostictus and the six carnivores for environmental axes tested. There was significant overlap with five of the carnivores on temperature and NDVI axes. On the precipitation axis, there was significant overlap between D. melanostictus with two species. Our results suggested that wide-ranging, locally rare carnivores may overlap extensively with D. melanostictus. The six carnivores that inhabit the eastern rainforest of Madagascar will likely share multiple, niche axes with this novel potential prey item. Species that eat the non-native common toad and are susceptible to its toxins are at conservation risk because their populations may not be robust enough to adapt quickly to this threat. We advocate closely monitoring these emerging interactions and suggest a preemptive conservation strategy for carnivores potentially at risk. |
Considering transient population dynamics in the conservation of slow life-history species: an application to the sandhill crane. Biological Conservation.
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Authors: Gerber, BD and Kendall, WC.
https://doi.org/10.1016/j.biocon.2016.06.014 Abstract: The importance of transient dynamics of structured populations is increasingly recognized in ecology, yet these implications are not largely considered in conservation practices. We investigate transient and long-term population dynamics to demonstrate the process and utility of incorporating transient dynamics into conservation research and to better understand the population management of slow life-history species; these species can be theoretically highly sensitive to short- and long-term transient effects. We are specifically interested in the effects of anthropogenic removal of individuals from populations, such as caused by harvest, poaching, translocation, or incidental take. We use the sandhill crane (Grus canadensis) as an exemplar species; it is long-lived, has low reproduction, late maturity, and multiple populations are subject to sport harvest. We found sandhill cranes to have extremely high potential, but low likelihood for transient dynamics, even when the population is being harvested. The typically low population growth rate of slow life-history species appears to buffer against many perturbations causing large transient effects. Transient dynamics will dominate population trajectories of these species when stage structures are highly biased towards the younger and non-reproducing individuals, a situation that may be rare in established populations of long-lived animals. However, short-term transient population growth can be highly sensitive to vital rates that are relatively insensitive under equilibrium, suggesting that stage structure should be known if perturbation analysis is used to identify effective conservation strategies. For populations of slow life-history species that are not prone to large perturbations to their most productive individuals, population growth may be approximated by equilibrium dynamics. |
Power pole density informs spatial prioritization for mitigating avian electrocution. Journal of Wildlife Management.
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Authors: Dwyer, JF, Harness, RE, Gerber, BD, Landon, MA, Petersen, P, Austin, D, and Eccleston, D.
https://doi.org/10.1002/jwmg.1048 Abstract: Raptor and corvid electrocutions cause continental conservation concerns for breeding, migrating, and wintering birds. Although concerns are widespread, mitigation is implemented primarily at local scales of individual electric utilities. By not considering landscape‐scale patterns, conservation strategies may fail to focus mitigation where efforts are needed most. To enable resource managers to consider electrocution risk at larger scales, we developed a regional model of distribution power pole (pole) density in a grid of 1‐km2 cells throughout Colorado and Wyoming. To do so, we obtained data on pole locations from a sample of electric utilities covering 31% of Colorado and Wyoming, and developed a predictive model of poles throughout the remainder of the 2 states. Pole density was influenced by road lengths, number of oil and gas wells, slope, development, and land cover. Poles were densest in areas with high road lengths, high numbers of wells, and relatively flat terrain, and in areas developed for agriculture or human residences. When model predictions are viewed together with species‐specific habitat maps, locations where high pole densities overlap habitat suggest areas where mitigating electrocution risk could be prioritized. Communication between resource managers and local utilities could then clarify the poles that caused the highest risk to raptors from electrocution. Thus, the model provides a framework for systematic spatial prioritization in support of regional conservation planning to minimize electrocution of raptors and corvids. |
2015
Optimal population prediction of sandhill crane recruitment based on climate-mediated
habitat limitations. Journal of Animal Ecology.
habitat limitations. Journal of Animal Ecology.
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Authors: Gerber, BD, Kendall, WL, Hooten, MB, Dubovsky, JA, and Drewien, RC.
https://doi.org/10.1111/1365-2656.12370 Abstract:
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When the carnivores roam: temporal partitioning among Madagascar's native and exotic carnivores.
Journal of ZoologY.
Journal of ZoologY.
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Authors: Farris, Z, Gerber, BD, Karpanty, SM, Murphy, A*, Andrianjakarivelo V, Ratelolahy, F, and Kelly, M.
https://doi.org/10.1111/jzo.12216 Abstract: Madagascar's Eupleridae carnivores are perhaps the least studied and most threatened family of Carnivora. Investigating potential direct and indirect competition among these native species and sympatric exotic carnivores is necessary to better direct conservation actions. From 2008 to 2013, we photographically surveyed a diverse rainforest landscape, comparing six native and three exotic carnivores' activity patterns throughout the diel cycle. We used hierarchical Bayesian Poisson analysis to describe the activity patterns of Madagascar's carnivore community, assessed effects of season and site on temporal activity patterns, and estimated coefficients of overlap between carnivore pairings to assess effects of body size and ecological niche on temporal overlap among native and exotic carnivores. We observed changes in temporal activity patterns across seasons particularly during the austral summer (hot–dry season) for four native and two exotic carnivores, including evidence of fossa Cryptoprocta ferox altering their temporal activity during their mating season (hot–dry season). We found evidence of high overlap between natives and exotics indicating the potential for increased interactions and competition. The greatest overlap in temporal activity occurred between both ring‐tail Galidia elegans and brown‐tail vontsira Salanoia concolor and exotic dogs Canis familiaris. Cr. ferox, falanouc Eupleres goudotii and spotted fanaloka Fossa fossana also overlapped in activity with the nocturnal, exotic Indian civet Viverricula indica. Cr. ferox avoided humans and Ca. familiaris across all seasons. Unexpectedly, carnivore body size and ecological niche were not important predictors of temporal overlap. Previous research has shown these native and exotic carnivores overlap spatially and these new findings of temporal overlap among native and exotic carnivores add urgency to the need to manage exotic carnivores across Madagascar. |
Spatial capture-recapture model performance with known small-mammal densities. Ecological Applications.
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Authors: Gerber, BD and Parmenter, RR.
https://doi.org/10.1890/14-0960.1 Abstract: Abundance and density of wild animals are important ecological metrics. However, estimating either is fraught with challenges; spatial capture–recapture (SCR) models are a relatively new class of models that attempt to ameliorate common challenges, providing a statistically coherent framework to estimate abundance and density. SCR models are increasingly being used in ecological and conservation studies of mammals worldwide, but have received little testing with empirical field data. We use data collected via a web and grid sampling design to evaluate the basic SCR model where small‐mammal abundance (N) and density (D) are known (via exhaustive sampling). We fit the basic SCR model with and without a behavioral effect to 11 small‐mammal populations for each sampling design using a Bayesian and likelihood SCR modeling approach. We compare SCR and ad hoc density estimators using frequentist performance measures. We found Bayesian and likelihood SCR estimates of density (D̂) and abundance (N̂) to be similar. We also found SCR models to have moderately poor frequentist coverage of D and N (45–73%), high deviation from truth (i.e., accuracy; D̂, 17–29%; N̂, 16–29%), and consistent negative bias across inferential paradigms, sampling designs, and models. With the trapping grid data, the basic SCR model generally performed more poorly than the best ad hoc estimator (behavior CR super‐population estimate divided by the full mean maximum distance moved estimate of the effective trapping area), whereas with the trapping web data, the best‐performing SCR model (null) was comparable to the best distance model. Relatively poor frequentist SCR coverage resulted from higher precision (SCR coefficients of variation [CVs] < ad hoc CVs); however D̂ and D were fairly well correlated (r2 range of 0.77–0.96). SCR's negative relative bias (i.e., average underestimation of the true density) suggests additional heterogeneity in detection and/or that small mammals maintained asymmetric home ranges. We suggest caution in the use of the basic SCR model when trapping animals in a sampling grid and more generally when small sample sizes necessitate the spatial scale parameter (σ) apply to all individuals. When possible, researchers should consider variation in detection and incorporate individual biological and/or ecological variation at the trap level when modeling σ. |
Assessing carnivore distribution from local knowledge across a human-dominated landscape in central-southeastern Madagascar. Animal Conservation.
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Authors: Kotschwar-Logan, M, Gerber, BD, Karpanty, SM, Justin, S, and Rabenahy, F.
https://doi.org/10.1111/acv.12137 Abstract: Carnivores are often sensitive to habitat loss and fragmentation, both of which are widespread in Madagascar. Clearing of forests has led to a dramatic increase in highly disturbed, open vegetation communities dominated by humans. In Madagascar's increasingly disturbed landscape, long‐term persistence of native carnivores may be tied to their ability to occupy or traverse these disturbed areas. However, how Malagasy carnivores are distributed in this landscape and how they interact with humans are unknown, as past research has concentrated on populations within continuous and fragmented forests. We investigated local ecological knowledge of carnivores using semi‐structured interviews in communities 0 to 20 km from the western edge of continuous rainforest in central‐southeastern Madagascar. Responses from 182 interviews in 17 different communities indicated distinct distribution patterns for two native and two exotic carnivore species, suggesting a range of tolerances to the human‐dominated landscape. The largest extant native carnivore, the fossa Cryptoprocta ferox, does not persist in much of this landscape; they were only observed in communities < 5 km from the continuous forest within the last five years. In contrast, the ring‐tailed mongoose Galidia elegans was observed by most communities (82%), but was observed by a higher proportion of interviewees from communities in close proximity to continuous forest. The exotic small Indian civet Viverricula indica was ubiquitous, while the exotic/feral cat (Felis sp.) was observed by a higher proportion of interviewees in communities farther from continuous forest. Over 20% of interviewees had experienced loss of poultry to wild carnivores in the last year and negative perceptions of carnivores were common. We found the human‐dominated landscape to provide little conservation value to native carnivores, emphasizing the need for adequate protected areas and increased engagement of local communities to sustain Madagascar's carnivore species. This information is critical to multitaxon conservation planning in Madagascar. |
2014
Teeth, sex, and testosterone: Aging in the world's smallest primate. PLOS ONE.
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Authors: Zohdy, S, Gerber, BD, Tecot, S, Blanco, MB,Wright, PC, and Jernvall, J.
https://doi.org/10.1371/journal.pone.0109528 Abstract: Mouse lemurs (Microcebus spp.) are an exciting new primate model for understanding human aging and disease. In captivity, Microcebus murinus develops human-like ailments of old age after five years (e.g., neurodegeneration analogous to Alzheimer's disease) but can live beyond 12 years. It is believed that wild Microcebus follow a similar pattern of senescence observed in captive animals, but that predation limits their lifespan to four years, thus preventing observance of these diseases in the wild. Testing whether this assumption is true is informative about both Microcebus natural history and environmental influences on senescence, leading to interpretation of findings for models of human aging. Additionally, the study of Microcebus longevity provides an opportunity to better understand mechanisms of sex-biased longevity. Longevity is often shorter in males of species with high male-male competition, such as Microcebus, but mouse lemurs are sexually monomorphic, suggesting similar lifespans. We collected individual-based observations of wild brown mouse lemurs (Microcebus rufus) from 2003–2010 to investigate sex-differences in survival and longevity. Fecal testosterone was measured as a potential mechanism of sex-based differences in survival. We used a combination of high-resolution tooth wear techniques, mark-recapture, and hormone enzyme immunoassays. We found no dental or physical signs of senescence in M. rufus as old as eight years (N = 189, ages 1–8, mean = 2.59±1.63 SE), three years older than captive, senescent congeners (M. murinus). Unlike other polygynandrous vertebrates, we found no sex difference in age-dependent survival, nor sex or age differences in testosterone levels. While elevated male testosterone levels have been implicated in shorter lifespans in several species, this is one of the first studies to show equivalent testosterone levels accompanying equivalent lifespans. Future research on captive aged individuals can determine if senescence is partially a condition of their captive environment, and studies controlling for various environmental factors will further our understanding of senescence. |
Recommended survey designs for occupancy modeling using motion-activated cameras: insights from empirical wildlife data. PeerJ.
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Authors: Shannon, G, Lewis, J, and Gerber, BD.
https://doi.org/10.7717/peerj.532 Abstract: Motion-activated cameras are a versatile tool that wildlife biologists can use for sampling wild animal populations to estimate species occurrence. Occupancy modelling provides a flexible framework for the analysis of these data; explicitly recognizing that given a species occupies an area the probability of detecting it is often less than one. Despite the number of studies using camera data in an occupancy framework, there is only limited guidance from the scientific literature about survey design trade-offs when using motion-activated cameras. A fuller understanding of these trade-offs will allow researchers to maximise available resources and determine whether the objectives of a monitoring program or research study are achievable. We use an empirical dataset collected from 40 cameras deployed across 160 km2 of the Western Slope of Colorado, USA to explore how survey effort (number of cameras deployed and the length of sampling period) affects the accuracy and precision (i.e., error) of the occupancy estimate for ten mammal and three virtual species. We do this using a simulation approach where species occupancy and detection parameters were informed by empirical data from motion-activated cameras. A total of 54 survey designs were considered by varying combinations of sites (10–120 cameras) and occasions (20–120 survey days). Our findings demonstrate that increasing total sampling effort generally decreases error associated with the occupancy estimate, but changing the number of sites or sampling duration can have very different results, depending on whether a species is spatially common or rare (occupancy = ψ) and easy or hard to detect when available (detection probability = p). For rare species with a low probability of detection (i.e., raccoon and spotted skunk) the required survey effort includes maximizing the number of sites and the number of survey days, often to a level that may be logistically unrealistic for many studies. For common species with low detection (i.e., bobcat and coyote) the most efficient sampling approach was to increase the number of occasions (survey days). However, for common species that are moderately detectable (i.e., cottontail rabbit and mule deer), occupancy could reliably be estimated with comparatively low numbers of cameras over a short sampling period. We provide general guidelines for reliably estimating occupancy across a range of terrestrial species (rare to common: ψ = 0.175–0.970, and low to moderate detectability: p = 0.003–0.200) using motion-activated cameras. Wildlife researchers/managers with limited knowledge of the relative abundance and likelihood of detection of a particular species can apply these guidelines regardless of location. We emphasize the importance of prior biological knowledge, defined objectives and detailed planning (e.g., simulating different study-design scenarios) for designing effective monitoring programs and research studies. |
Primates and Cameras. International Journal of Primatology.
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Authors: Gerber, BD, Williams, PJ, and Bailey, LL.
http://doi.org./10.1007%2Fs10764-014-9761-9 Abstract: Field-based primate studies often make population inferences using count-based indices (e.g., individuals/plot) or distance sampling; the first does not account for the probability of detection and thus can be biased, while the second requires large sample sizes to obtain precise estimates, which is difficult for many primate studies. We discuss photographic sampling and occupancy modeling to correct for imperfect detection when estimating system states and dynamics at the landscape level, specifically in relation to primate ecology. We highlight the flexibility of the occupancy framework and its many applications to studying low-density primate populations or species that are difficult to detect. We discuss relevant sampling and estimation procedures with special attention to data collection via photographic sampling. To provide tangible meaning to terminology and clarify subtleties, we use illustrative examples. Photographic sampling can have many advantages over observer-based sampling, especially when studying rare or elusive species. Combining photographic sampling with an occupancy framework allows inference to larger scales than is common in primate studies, addresses uncertainty due to the observation process, and allows researchers to examine questions of how landscape-level anthropogenic changes affect primate distributions. |
Estimating the abundance of rare and elusive carnivores from photographic-sampling data when the population size is very small. Population Ecology.
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Authors: Gerber, BD, Ivan, JS, and Burnham, KP.
https://doi.org/10.1007/s10144-014-0431-8 Abstract: Conservation and management agencies require accurate and precise estimates of abundance when considering the status of a species and the need for directed actions. Due to the proliferation of remote sampling cameras, there has been an increase in capture–recapture studies that estimate the abundance of rare and/or elusive species using closed capture–recapture estimators (C–R). However, data from these studies often do not meet necessary statistical assumptions. Common attributes of these data are (1) infrequent detections, (2) a small number of individuals detected, (3) long survey durations, and (4) variability in detection among individuals. We believe there is a need for guidance when analyzing this type of sparse data. We highlight statistical limitations of closed C–R estimators when data are sparse and suggest an alternative approach over the conventional use of the Jackknife estimator. Our approach aims to maximize the probability individuals are detected at least once over the entire sampling period, thus making the modeling of variability in the detection process irrelevant, estimating abundance accurately and precisely. We use simulations to demonstrate when using the unconditional‐likelihood M0 (constant detection probability) closed C–R estimator with profile‐likelihood confidence intervals provides reliable results even when detection varies by individual. If each individual in the population is detected on average of at least 2.5 times, abundance estimates are accurate and precise. When studies sample the same species at multiple areas or at the same area over time, we suggest sharing detection information across datasets to increase precision when estimating abundance. The approach suggested here should be useful for monitoring small populations of species that are difficult to detect. |
2013
Marking power lines reduces avian collisions near the Audubon National Wildlife Refuge, North
Dakota. Wildlife Society Bulletin.
Dakota. Wildlife Society Bulletin.
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Authors: Sporer,, MK, Dwyer, JF, Gerber, BD, Harness, RE, and Pandey, AK.
https://doi.org/10.1002/wsb.329 Abstract: Overhead power lines can pose collision risks to birds. Risks may be mitigated through marking lines with high‐visibility devices, but the effectiveness of line marking remains unclear. Effectiveness is particularly poorly described for lines bisecting open water, where detection of carcasses can be difficult. We marked 3 of 9 spans (lines between adjacent structures) along a causeway crossing open water and 2 adjacent spans over lake shores between Lake Sakakawea and Lake Audubon near Audubon National Wildlife Refuge, North Dakota, USA. Over 3 years, we found 1,186 avian carcasses, including 276 attributed to power‐line collision. American coots (Fulica americana; n = 83) and double‐crested cormorants (Phalacrocorax auritus; n = 27) were the species most commonly associated with power‐line collision, but we also found carcasses of 51 other species, including a piping plover (Charadrius melodus; n = 1). Multi‐variable modeling indicated line marking over open water reduced predicted collisions per span per season (mid‐April through mid‐October, 2006–2008) from 10.3 to 5.8. Birds with high‐aspect‐ratio wings benefitted most from line marking (e.g., shorebirds and gulls). If the 9 open‐water spans we studied were unmarked for 30 years, we predicted 2,775 collisions. We predicted only 1,560 collisions if all of these spans were marked. Our data demonstrate that a wide variety of avian species are at risk of collision with lines bisecting open water, marking lines can reduce collision risk, and because collisions persisted and some line markers fell off power lines, improvements to effectively mark lines are needed. © 2013 The Wildlife Society. |
Risky business: Sex Specific diFFerences in mortality and dispersal in a polygynous, monomorphic lemur. Behavioral Ecology.
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Authors: Tecot, S, Gerber, BD, King, SJ, Verdolin, JL, and Wright, PC.
https://doi.org/10.1093/beheco/art008 Abstract: Sexually selected traits and the use of strategies to enhance male reproductive success (e.g., competition and dispersal) can yield sex differences in metabolic requirements, rates and durations of growth and maturation, and the propensity for risky behavior, which are suggested to result in age-specific sex differences in mortality and life span. We investigated age-specific sex ratios, mortality, and dispersal in Propithecus edwardsi in Ranomafana National Park, Madagascar. We predicted that, due to similarities in growth rates and body sizes, male and female juvenile mortality rates would be comparable; because both sexes disperse and have intense intersexual competition and aggression, adult mortality would be similar; given similarities in dispersal frequency and distance, the timing of dispersal would not differ. We used 80 group-years births, deaths, and dispersals (Nfemales = 41, Nmales = 34) collected over 23 years to calculate sex ratios and survival curves. Females lived longer than males (maximum 32 and 19 years, respectively). Sex ratios were male biased from sexual maturity through 17 years and female biased at birth and older ages. Infant survival probabilities were similar. Thus, differential development and maturation are unlikely explanations for longer female life span in this species. Males were more likely to survive from 2 to 18 years. However, male annual survival probability declined quickly around 13–18 years; males continued to disperse until their deaths, whereas females generally stopped dispersing after 11 years. We suggest that sex differences in the timing of dispersal and the unique challenges of risky behavior at older ages may be sufficient to yield differences in male and female life span. |
2012
The impact of forest logging and fragmentation on carnivore species composition, density, and occupancy in Madagascar's southeastern rainforests. Oryx.
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Authors: Gerber, BD, Karpanty, SM, and Randrianantenaina, J.
https://doi.org/10.1017/S0030605311001116 Abstract: Forest carnivores are threatened globally by logging and forest fragmentation yet we know relatively little about how such change affects predator populations. This is especially true in Madagascar, where carnivores have not been extensively studied. To understand better the effects of logging and fragmentation on Malagasy carnivores we evaluated species composition, density of fossa Cryptoprocta ferox and Malagasy civet Fossa fossana, and carnivore occupancy in central-eastern Madagascar. We photographically-sampled carnivores in two contiguous (primary and selectively-logged) and two fragmented rainforests (fragments <2.5 and >15 km from intact forest). Species composition varied, with more native carnivores in the contiguous than fragmented rainforests. F. fossana was absent from fragmented rainforests and at a lower density in selectively-logged than in primary rainforest (mean 1.38±SE 0.22 and 3.19±SE 0.55 individuals km−2, respectively). C. ferox was detected in fragments <2.5 km from forest and had similar densities in primary and selectively-logged forests (0.12±SE 0.05 and 0.09±SE 0.04 adults km−2, respectively) but was absent in fragments >15 km from forest. We identified only two protected areas in Madagascar that may maintain >300 adult C. ferox. Occupancy of broad-striped mongoose Galidictis fasciata was positively related to fragment size whereas occupancy of ring-tailed mongoose Galidia elegans elegans was negatively associated with increasing exotic wild cat (Felis spp.) activity at a camera site. Degraded rainforest fragments are difficult environments for Malagasy carnivores to occupy; there is a need to prioritize the reconnection and maintenance of contiguous forest tracts. |
Activity patterns of carnivores in the rain forests of Madagascar: implications for species coexistence.
Journal of Mammalogy.
Journal of Mammalogy.
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Authors: Gerber, BD, Karpanty, SM, and Randrianantenaina, J.
https://doi.org/10.1644/11-MAMM-A-265.1 Abstract: Temporal partitioning of activity among sympatric species can be an important mechanism for species coexistence. Further, if exotic and native species overlap temporally, there is potential for direct competition and antagonism, which may lead to native species extirpation. We 1st assessed if ecologically similar native carnivores of Madagascar demonstrated activity pattern overlap and then explored whether overlap in activity might lead to negative impacts of exotic carnivores on native carnivores. We used photographic sampling to quantify the temporal activity patterns of carnivores at 4 study sites. The activity of the 2 smaller-bodied native species, Galidia elegans and Galidictis fasciata, overlapped minimally; these 2 carnivores share a similar generalist diet, which may drive their divergent temporal activity. In contrast, the medium-sized native species, Fossa fossana and Eupleres goudotii, were both highly nocturnal; these 2 species appear segregated in their diets. The largest native carnivore, Cryptoprocta ferox, selectively used crepuscular hours, but overall was cathemeral; it was notably absent or basically so at sites where dogs were most abundant and active throughout the diel cycle. We found G. elegans to shift from preferred activity periods in the presence of dogs and the exotic Viverricula indica. Our results suggest that the presence and activity of exotic carnivores can negatively impact native carnivores in fragmented rain forests. |
Spatial ecology of the endangered Milne-Edwards sifaka (Propithecus edwardsi): Dologging and season a ect home range and daily ranging patterns? International Journal of Primatology.
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Authors: Gerber, BD, Arrigo-Nelson, S, Karpanty, S, Kotschwar, M, and Wright, PC.
https://doi.org/10.1007/s10764-011-9576-x Abstract: Primates often live in human-altered habitats; Malagasy lemurs are no exception. It is important to understand if habitat alteration affects primates’ space use patterns across multiple spatial and temporal scales, as this drives population density. We quantified the daily, seasonal, and annual space-use of seven groups of Milne-Edwards’ sifaka (Propithecus edwardsi) living in unlogged and logged rain forest in Ranomafana National Park, Madagascar between December 2002 and November 2003. Concurrent data showed that sifakas consumed higher quality foods in the unlogged than in logged forests; thus we explored how space use patterns were related to energy use strategies. Sifaka groups in the logged rain forest traveled 7–13% less per day than groups in the unlogged rain forest, despite their larger home ranges (median: 46.12 and 23.52 ha, in the logged and unlogged forests, respectively). Sifakas may thus use an energy-minimizing strategy at the scale of the individual day but an energy-maximizing strategy at the annual home range scale. Sifakas exhibited fidelity to the home range across seasons, but their core area of use shifted considerably with season. We found no difference in population density between sites. However, given the interannual variability in sifaka foods, a multiyear study is needed to assess if energy strategies observed in this study are consistent across longer time periods. Our findings suggest that lemurs may persist in logged habitats by altering spatial use patterns; future work should attempt to quantify the threshold level of forest regeneration from logging that will allow lemurs to persist at similar densities as in unlogged forest. |
Evaluating the potential biases in carnivore capture-recapture studies associated with the use of lure and varying density estimation techniques using photographic-sampling data of the Malagasy civet.
Population Ecology.
Population Ecology.
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Authors: Gerber, BD, Karpanty, SM, and Kelly, MJ
https://doi.org/10.1007/s10144-011-0276-3 Abstract: Estimating density of elusive carnivores with capture–recapture analyses is increasingly common. However, providing unbiased and precise estimates is still a challenge due to uncertainties arising from the use of (1) bait or lure to attract animals to the detection device and (2) ad hoc boundary‐strip methods to compensate for edge effects in area estimation. We used photographic‐sampling data of the Malagasy civet Fossa fossana collected with and without lure to assess the effects of lure and to compare the use of four density estimators which varied in methods of area estimation. The use of lure did not affect permanent immigration or emigration, abundance and density estimation, maximum movement distances, or temporal activity patterns of Malagasy civets, but did provide more precise population estimates by increasing the number of recaptures. The spatially‐explicit capture–recapture (SECR) model density estimates ±SE were the least precise as they incorporate spatial variation, but consistent with each other (Maximum likelihood‐SECR = 1.38 ± 0.18, Bayesian‐SECR = 1.24 ± 0.17 civets/km2), whereas estimates relying on boundary‐strip methods to estimate effective trapping area did not incorporate spatial variation, varied greatly and were generally larger than SECR model estimates. Estimating carnivore density with ad hoc boundary‐strip methods can lead to overestimation and/or increased uncertainty as they do not incorporate spatial variation. This may lead to inaction or poor management decisions which may jeopardize at‐risk populations. In contrast, SECR models free researchers from making subjective decisions associated with boundary‐strip methods and they estimate density directly, providing more comparable and valuable population estimates. |
2011
Day and night foraging of Red knots (Calidris canutus) during spring stopover in Virginia, USA. Waterbirds.
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Authors: Cohen, JB, Gerber, BD, Karpanty, SM, Fraser, JD, and Truitt, BR.
https://doi.org/10.1675/063.034.0309 Abstract: Long-jump migrant shorebirds have brief windows during spring stopover to acquire the energy needed to complete migration. Red Knots (Calidris canutus) refueling on Horseshoe Crab (Limulus polyphemus) eggs in Delaware Bay can meet their energy needs foraging only by day. In nearby Virginia, thousands of Red Knots stop over, but primarily low-quality, hard-shelled prey are available. One tactic Red Knots may use to meet their energy demands with such prey might be to extend their foraging time by feeding at night. To estimate the length of the foraging day in Virginia, daylight feeding was studied during three spring stopover periods (2008 to 2010), and night feeding was studied in 2010. Red Knots foraged 76 ± 3 SE% of the time in 2008 and 2009 combined, and 59 ± 3% of the time in 2010, during 3-minute observations. In 2010, Red Knots foraged 51 ± 7% of the time during a continuous 7-h daytime observation and 77 ± 5% of the time during a continuous 8-h night time observation on the same island. Given constraints on energy intake, night foraging by Red Knots in Virginia may be necessary for birds to attain sufficient mass to complete migration. |
2010
An assessment of carnivore relative abundance and density in the eastern rainforests of Madagascar using remotely-triggered camera traps. Oryx
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Authors: Gerber, BD, Karpanty, SM, Crawford, C, Kotschwar, M, and Randrianantenaina, J.
http://doi.org/10.1017/S0030605309991037 Abstract: Despite major efforts to understand and conserve Madagascar’s unique biodiversity, relatively little is known about the island’s carnivore populations. We therefore deployed 43 camera-trap stations in Ranomafana National Park, Madagascar during June–August 2007 to evaluate the efficacy of this method for studying Malagasy carnivores and to estimate the relative abundance and density of carnivores in the eastern rainforest. A total of 755 camera-trap nights provided 1,605 photographs of four endemic carnivore species (fossa Cryptoprocta ferox, Malagasy civet Fossa fossana, ring-tailed mongoose Galidia elegans and broad-striped mongoose Galidictus fasciata), the exotic Indian civet Viverricula indica and the domestic dog Canis familiaris. We identified 38 individual F. fossana and 10 individual C. ferox. We estimated density using both capture-recapture analyses, with a buffer of full mean-maximum-distance-moved, and a spatially-explicit maximum-likelihood method (F. fossana: 3.03 and 2.23 km-2, respectively; C. ferox: 0.15 and 0.17 km-2, respectively). Our estimated densities of C. ferox in rainforest are lower than published estimates for conspecifics in the western dry forests. Within Ranomafana National Park species richness of native carnivores did not vary among trail systems located in secondary, selectively-logged and undisturbed forest. These results provide the first assessment of carnivore population parameters using camera-traps in the eastern rainforests of Madagascar. |
Book Chapters
The new natural history of Madagascar. ed. S. M. Goodman. PRINCETON, PRINCETON UNIVERSITY PRESS.
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Camera Trapping Madagascar
Farris, ZJ, Gerber, BD, Murphy, A*, and Wampole, E* |
(In press)
Small Carnivores: Evolution, Ecology, Behaviour & Conservation. E. Do Linh San, JL. Sato, JL. Belant, & MJ
Somers, Eds. Oxford, Wiley-Blackwell.
Somers, Eds. Oxford, Wiley-Blackwell.
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Spatio-temporal overlap between a native and exotic carnivore in Madagascar: evidence of competitive exclusion Farris, Z, Gerber, BD, Kelly, M, Karpanty, SM, Ratelolahy, F, and Andrianjakarivelo V. (In press) |
Terrestrial Ecosystems and Biodiversity, The Handbook of Natural Resources, Second Edition. Yeqiao Wang, Eds. CRC Press.
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DECISION MAKING AND MONITORING STRATEGIES IN NATURAL RESOURCE MANAGEMENT AND CONSERVATION Gerber, BD and Williams, PJ. 2020 |
Program MARK - A Gentle Introduction E. Cooch, Ed.
The Birds of North America Online. A. Poole, Ed. Ithaca: Cornell Lab of Ornithology; Birds of North America
Online
Online
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Sandhill Crane (Grus Canadensis) Gerber, BD, Dwyer, JD, Nesbitt, SA, Drewien, RC, Little ELD CD, Tacha, TC, and Vohs, PA. 2014 |
