A dynamic multi-scale occupancy model to estimate temporal dynamics and hierarchical habitat use for nomadic species

Distribution models are increasingly being used to understand how landscape and climatic changes are affecting the processes driving spatial and temporal distributions of plants and animals. However, many modeling efforts ignore the dynamic processes that drive distributional patterns at different scales, which may result in misleading inference about the factors influencing species distributions. Current occupancy models allow estimation of occupancy at different scales and, separately, estimation of immigration and emigration. However, joint estimation of local extinction, colonization, and occupancy within a multi-scale model is currently unpublished. We extended multi-scale models to account for the dynamic processes governing species distributions, while concurrently modeling local-scale availability. We fit the model to data for lark buntings and chestnut-collared longspurs in the Great Plains, USA, collected under the Integrated Monitoring in Bird Conservation Regions program. We investigate how the amount of grassland and shrubland and annual vegetation conditions affect bird occupancy dynamics and local vegetation structure affects fine-scale occupancy. Buntings were prevalent and longspurs rare in our study area, but both species were locally prevalent when present. Buntings colonized sites with preferred habitat configurations, longspurs colonized a wider range of landscape conditions, and site persistence of both was higher at sites with greener vegetation. Turnover rates were high for both species, quantifying the nomadic behavior of the species. Our model allows researchers to jointly investigate temporal dynamics of species distributions and hierarchical habitat use. Our results indicate that grassland birds respond to different covariates at landscape and local scales suggesting different conservation goals at each scale. High turnover rates of these species highlight the need to account for the dynamics of nomadic species, and our model can help inform how to coordinate management efforts to provide appropriate habitat configurations at the landscape scale and provide habitat targets for local managers.

Simulations inform design of regional occupancy-based monitoring for a sparsely distributed, territorial species

Sparsely distributed species attract conservation concern, but insufficient information on population trends challenges conservation and funding prioritization. Occupancy-based monitoring is attractive for these species, but appropriate sampling design and inference depend on particulars of the study system. We employed spatially explicit simulations to identify minimum levels of sampling effort for a regional occupancy monitoring study design, using white-headed woodpeckers (Picoides albolvartus), a sparsely distributed, territorial species threatened by habitat decline and degradation, as a case study. We compared the original design with commonly proposed alternatives with varying targets of inference (i.e., species range, space use, or abundance) and spatial extent of sampling. Sampling effort needed to achieve adequate power to observe a long-term population trend (≥80% chance to observe a 2% yearly decline over 20 years) with the previously used study design consisted of annually monitoring ≥120 transects using a single-survey approach or ≥90 transects surveyed twice per year using a repeat-survey approach. Designs that shifted inference toward finer-resolution trends in abundance and extended the spatial extent of sampling by shortening transects, employing a single-survey approach to monitoring, and incorporating a panel design (33% of units surveyed per year) improved power and reduced error in estimating abundance trends. In contrast, efforts to monitor coarse-scale trends in species range or space use with repeat surveys provided extremely limited statistical power. Synthesis and applications. Sampling resolutions that approximate home range size, spatially extensive sampling, and designs that target inference of abundance trends rather than range dynamics are probably best suited and most feasible for broad-scale occupancy-based monitoring of sparsely distributed territorial animal species.

Survival of fishers in the southern Sierra Nevada region of California

Fishers in the western United States were recently proposed for listing under the U.S. Endangered Species Act because of concerns for loss of suitable habitat and evidence of a diversity of mortality risks that reduce survival. One of 2 remnant populations of fishers in California is in the southern Sierra Nevada region, where we studied them at 2 research sites in the Sierra National Forest. Our objectives were to evaluate whether survival was lower for male fishers and dispersal-aged individuals or if survival varied seasonally. We captured and monitored 232 radiocollared fishers from March 2007 to March 2014 and used model analyses to identify important predictors of survival. Fifty-two percent ( n = 120) of the radiocollared fishers died, and survival varied by sex and season, but not by age or between study sites. There was no evidence that dispersal-aged fishers experienced lower survival than older fishers. Annual survival trended lower for male (0.62 [95% CI 0.54–0.70]) compared to female fishers (0.72 [95% CI 0.67–0.78]), was lowest in the spring to mid-summer season (0.83 [95% CI 0.78–0.87]), and highest in late fall and winter (0.92 [95% CI 0.89–0.94]). Lower survival among male fishers appeared linked to males moving over large areas to locate mates, while lower survival for females was potentially related to high energetic cost of reproduction. It was possible but unknown if lower survival among all fishers in spring was linked to secondary exposure to toxicants dispersed around illicit marijuana grow sites. Six-month survival of juvenile fishers was 0.85 for females and 0.79 for males, but lower at 0.62 for females and 0.57 for males when adjusted for deaths before late September. Annual survival among adult female fishers was 20% lower than 0.90, a value that prior modeling suggested was required for population expansion in the overall southern Sierra Nevada. Survival data from our study imply a greater challenge for maintaining self-sustaining fisher populations in the southern Sierra Nevada region, and resource managers are working to mitigate several of the human-associated factors that limit population growth.

Patterns of Natural and Human-Caused Mortality Factors of a Rare Forest Carnivore, the Fisher (Pekania pennanti) in California

Wildlife populations of conservation concern are limited in distribution, population size and persistence by various factors, including mortality. The fisher (Pekania pennanti), a North American mid-sized carnivore whose range in the western Pacific United States has retracted considerably in the past century, was proposed for threatened status protection in late 2014 under the United States Endangered Species Act by the United States Fish and Wildlife Service in its West Coast Distinct Population Segment. We investigated mortality in 167 fishers from two genetically and geographically distinct sub-populations in California within this West Coast Distinct Population Segment using a combination of gross necropsy, histology, toxicology and molecular methods. Overall, predation (70%), natural disease (16%), toxicant poisoning (10%) and, less commonly, vehicular strike (2%) and other anthropogenic causes (2%) were causes of mortality observed. We documented both an increase in mortality to (57% increase) and exposure (6%) from pesticides in fishers in just the past three years, highlighting further that toxicants from marijuana cultivation still pose a threat. Additionally, exposure to multiple rodenticides significantly increased the likelihood of mortality from rodenticide poisoning. Poisoning was significantly more common in male than female fishers and was 7 times more likely than disease to kill males. Based on necropsy findings, suspected causes of mortality based on field evidence alone tended to underestimate the frequency of disease-related mortalities. This study is the first comprehensive investigation of mortality causes of fishers and provides essential information to assist in the conservation of this species.