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At least 433 records · Page 24Linked to original sources

USGS2022

Understory structure and heterospecifics influence the occupancy of a ground-nesting species of conservation concern, the Canada Warbler

Forest structure and composition in eastern U.S. forests are changing because of forest regeneration after farmland abandonment, less frequent occurrence of severe disturbances, and climate change. Some of these changes may disproportionally affect birds that rely on gap dynamics or other forest canopy disturbances to create understory habitat. The Canada Warbler ( Cardellina canadensis ) is one such understory specialist that has undergone consistent declines. We assessed environmental and interspecific factors associated with Canada Warbler space use in its southern breeding distribution to understand potential causes of population declines and inform conservation efforts. We evaluated Canada Warbler occupancy from 840 point count surveys conducted in 2017 and 2018 at 470 unique locations (79% of locations surveyed in both years) throughout Monongahela National Forest, West Virginia, USA. We modeled Canada Warbler occupancy probability as a function of environmental variables and included Black-throated Blue Warbler ( Setophaga caerulescens ) and Hermit Thrush ( Catharus guttatus ) as interacting species because all three species exhibit similar habitat preferences. Canada Warblers were most likely to occur in areas with rhododendron ( Rhododendron maximum ) density > 0.27 stems/m² and within 3 m of riparian areas (streams and wetlands). They were also more likely to occur in mid-elevation (highest occupancy at 930 m) northern hardwood forests when Black-throated Blue Warblers were also present. Black-throated Blue Warblers were most likely to occupy mid-elevation sites with high shrub density, whereas Hermit Thrushes were more likely to occupy high-elevation, old-age forests. Potential management actions could focus on conserving riparian areas in northern hardwood forests, especially those with dense rhododendron thickets. Such potential actions could also be beneficial across the entire elevation range we explored within the region (500–1300 m). Canada Warblers may be benefiting from the recent spread of rhododendron habitats and northern hardwood forest types within West Virginia.

West Virginia↗

USGS2023

Full-service hotels, convenience stores, or fire escapes? Evaluating the functional role of stopover sites for Neotropical migrants following passage across the Gulf of Mexico in autumn

Nearctic Neotropical migratory songbirds incur the highest mortality during migration. En-route, songbirds rely on a network of stopover sites to rest, refuel, and/or seek refuge during poor weather. Conservation strategies prioritize protection of sites that best meet these needs. However, the specific function of a stopover site is expected to vary in relation to factors, such as geographic location, surrounding landscape, and weather. To identify sites with the highest conservation value for migratory songbirds, a conceptual framework was independently developed to classify sites into three functional categories based on their geographic and landscape features: fire escapes, convenience stores, and full-service hotels. The few attempts to empirically validate this framework have focused on temperate stopover sites. We evaluated the framework by testing the hypothesis that a site’s geographic and landscape characteristics can predict its function. We used capture and radio-tracking data at an island and mainland site in the Yucatan Peninsula, Mexico to quantify mean and variance in daily capture rate, body condition, stopover duration, and departure behavior during autumn, with a focus on four species: Swainson’s Thrush (Catharus ustulatus), Red-eyed Vireo (Vireo olivaceus), Gray Catbird (Dumetella carolinensis), and Prothonotary Warbler (Protonotaria citrea). Our results supported our predictions that the island functions as a fire escape, providing refuge for very high numbers of birds after encountering crosswinds or headwinds over the Gulf of Mexico, and the mainland forest site serves as a full-service hotel. The framework provides valuable insight for strategic conservation planning and management of stopover sites for songbirds. We suggest future studies evaluate the framework’s application to non-forest bird species. Additionally, we encourage collaborative efforts to consolidate and integrate tracking data, capture data from migration banding stations, and radar-based bird density estimates across a broad geography to test the framework’s ability to inform conservation planning across species’ full migratory range.

Avian Conservation and Ecology↗

USGS2024

Estimates of Southern White-tailed Ptarmigan daily nest survival from multiple sites in the Southern Rocky Mountains of Colorado

Estimating vital rates of avian species is important to understand population dynamics and develop potential conservation strategies that target rates for management. Avian species have reduced potential for high annual fecundity in alpine ecosystems due to a short breeding window and harsh weather conditions. We located nests from Southern White-tailed Ptarmigan ( Lagopus leucura altipetens ) across six study sites in the Southern Rocky Mountains of Colorado to estimate daily nest survival from 2013–2017. We used a known-fate hierarchical nest survival model and fit several covariates, including environmental conditions representing daily weather events and shrub cover, to describe variation in daily survival and derive estimates of nest success. We located and monitored 198 nests from 128 radio-marked ptarmigan hens. The mean nest success estimated as a derived parameter from daily nest survival was 45.6% (95% credible interval [CI]: 31.2–59.6%) and ranged from 40.3% to 50.3% across sites. Variation in daily nest survival was poorly described by the covariates we fit (95% CI of most slope coefficients overlapped 0), although there was some support for a negative effect of relative elevation (nests at lower elevations within a site survived at higher rates) and a positive effect of nest age (older nests survived at higher rates). We examined how variation in nest success was likely to influence the finite rate of population growth using a simple simulation with an age-transition matrix parameterized with previously reported fecundity and survival estimates. We found that the finite growth rate was predicted to increase 18.7% when evaluated from the lower to upper 95% CI estimated values of nest success, conditional on the other vital rates used in our simulation. We discuss the broader implications of these findings in the context of managing for nest survival of Southern White-tailed Ptarmigan.

Colorado↗

USGS2024

Response of corvid nest predators to thinning: implications for balancing short- and long-term goals for restoration of forest habitat

Forest thinning on public lands in the Pacific Northwest USA is an important tool for restoring diversity in forest stands with a legacy of simplified structure from decades of intensive management for timber production. A primary application of thinning in young (< 50-year-old) stands is to accelerate forest development to mitigate loss of late-seral habitat to decades of logging. However, thinning may have short-term negative effects for some species associated with mature forest that are expected to benefit from the practice over the long term. An increased risk of nest predation is a primary concern to managers charged with stewardship of habitat for the federally threatened Marbled Murrelet ( Brachyramphus marmoratus ), a species that nests in older forests. Predation by corvids is the greatest cause of nest failure for the Marbled Murrelet, and corvids are known to respond positively to forest disturbance, but quantitative information is lacking on the potential impacts of thinning on risk of nest predation. We investigated the response of two common corvid nest predators, Steller’s Jay ( Cyanocitta stelleri ) and Canada Jay ( Perisoreus canadensis ), to variation in thinning intensity in young forest (< 50 years old) using data from a long-term silviculture experiment. We used a Before-After-Control-Impact (BACI) design, linear mixed modeling, and occupancy modeling to quantify differences in corvid observation rates among varying levels of thinning intensity, and to assess changes in jay response over more than a decade following thinning. We found an increase in observation rates of both species in the heavily thinned treatment during the first 5 to 7 years following thinning, and some evidence of a short-term increase in Steller’s Jay activity in the thinning-with-gaps treatment. Neither jay species responded to the least intensive thinning treatment, which reduced average canopy cover by < 30%. By approximately a decade after thinning, observation rates of jays did not differ between unthinned controls and any of the thinning treatments. Incorporating our quantitative information into landscape-level planning can help managers balance short- and long-term conservation goals.

Oregon↗

USGS2024

Abundance of Long-billed Curlews on military lands in the Columbia Basin

Long-billed Curlews ( Numenius americanus ) are declining throughout North America, and the loss of grassland breeding habitat is one of the primary threats to the species. Intermountain West, in particular, has been identified as the most important region in North America for breeding curlews. Nevertheless, the density and abundance of Long-billed Curlews in this region is not well understood. Lands managed for military training can provide habitat for wildlife species of conservation concern, and increasingly these lands are becoming relevant to sustaining biodiversity. We conducted point count surveys of Long-billed Curlews on Department of Defense lands in the Columbia Basin near Boardman, Oregon, USA during two consecutive breeding seasons. We used multinomial-Poisson mixture models to estimate detection probability and density of curlews and to investigate environmental correlates of those metrics. Mean detection probability at a distance of 400 m was 0.45 and 0.61 in 2015 and 2016, respectively. In 2015, the clarity of skies increased detection probability, but in 2016, none of the variables we measured influenced detection probability. Mean predicted density was 3.3 (95% confidence interval: 2.4–4.7) and 1.8 (1.2–2.7) curlews/km² in 2015 and 2016, respectively. In both years, curlew density was higher in lower-elevation or topographically smoother areas. Estimated abundance of curlews in the study area was 639 (456–912) and 350 (237–520) birds in 2015 and 2016, respectively. The number of curlews appeared to fluctuate across the two years of our study, a demographic trend that may have been influenced by a wildfire in our study area in June 2015. The results of our study indicate that federal grasslands, including areas where military operations are conducted, can provide conservation benefit to breeding Long-billed Curlews.

Oregon↗

USGS2024

Geolocators, stable isotopes, and citizen science identify migratory timing, route, and spring molt of Smith’s Longspurs

Climate change is having a disproportionate impact on the Arctic. For Arctic breeding birds, basic knowledge of their annual cycle, specifically the timing, route, and movement behavior of migration, is needed to understand when and where populations may experience threats. We used a combination of geolocators and stable isotope analysis to identify route and timing of migration in Smith’s Longspurs ( Calcarius pictus ) that breed in Alaska’s Brooks Range. We trapped males on their breeding grounds from 2011 to 2014 and collected head feathers for stable isotopes of hydrogen (δ²H). We deployed 22 geolocators on a subset of individuals and retrieved four, which all overwintered in southern Texas. Individual start dates for fall migration based on geolocators were more variable than for the spring, and individuals were highly mobile while on their wintering grounds. Geolocators and stable isotope values were comparable across years and indicated that birds from the Brooks Range undergo their pre-nuptial molt in central Canada. We compared geolocator and stable isotope inferred locations to observations submitted to e-Bird and found that longspurs were distributed farther south during the winter months, but farther north during the spring than most eBird observations. Concurrent deployments of geolocator tags across Smith’s Longspurs’ breeding range would clarify whether migratory behaviors and routes are population-specific or shared widely across breeding locations.

Avian Conservation and Ecology↗

USGS2025

Sex differences in migration routes and non-breeding areas of a declining shorebird

Migratory birds face different threats and pressures across their annual cycle, and understanding the impact of these factors on individuals is critical to the conservation of avian populations. Individuals from the same breeding population may share the same non-breeding areas, and thus experience similar conditions, or they may travel to different habitats or regions during migration and the stationary non-breeding period. Marbled Godwits ( Limosa fedoa ) breeding in the Northern Great Plains, which have experienced steep population declines, are thought to spend the non-breeding period primarily on the Pacific Coast of the United States and Mexico. However, little is known about migratory routes, stopover sites, and non-breeding locations of specific breeding populations, nor whether individuals from the same breeding population remain together throughout the year. We deployed satellite transmitters on four mated pairs of godwits breeding in southern Alberta, Canada, with individuals tracked over a mean of 2.2 annual cycles (range 0.6–5.6, excluding one unit that stopped transmitting immediately following deployment). Counter to our expectations, females and males separated completely following breeding, with females traveling to non-breeding areas along the coast of California, United States, and males stopping over at Great Salt Lake, Utah, United States, and spending the non-breeding period in Baja California Sur, Mexico, a distance of ~1300 km from their mates. Despite spending nine months apart, individuals from this breeding population have previously been shown to have high mate fidelity. Interestingly, individuals mostly used protected areas during the non-breeding period, in contrast to the human-modified agricultural landscapes that make up the majority of their breeding grounds. Despite a small sample size, our results suggest a strong pattern of differential migration based on sex, with implications for the specific environmental conditions, and potentially threats, faced by female and male godwits across the annual cycle.

Avian Conservation and Ecology↗

USGS2025

Survival of captive-raised light-footed Ridgway’s rails is influenced by release date and time in wild

Captive breeding and translocation programs are an increasingly common conservation tool and management strategy used for some of the rarest and most endangered species in the world. These programs come at a high cost, and many translocation programs fail to monitor animals after release. Light-footed Ridgway’s rails ( Rallus obsoletus levipes ) are federally endangered marsh birds endemic to coastal wetlands of southern California and northern Mexico. Juvenile captive-raised light-footed Ridgway’s rails have been released into marshes within their U.S. range for >20 yr, but little effort has been devoted to post-release tracking of their movement and survival. We used satellite GPS transmitters to track survival of 46 juvenile captive-released and 42 juvenile wild-caught light-footed Ridgway’s rails from 2020–2022. Our results suggest that juvenile captive-released rails had lower initial daily survival probability (0.979) compared with that of juvenile wild-caught rails (0.994). Survival probability of captive-released rails increased with time in the wild, matching that of wild birds at about 100 d post-release. Survival of captive-released birds was most influenced by the date birds were released (releases in early summer had the highest survival). Our study emphasizes the importance of post-release monitoring as part of any captive breeding and translocation program and provides important insight into management strategies that may improve captive-released rail survival in the wild.

California↗

USGS2025

The continued decline of the Palila (Loxioides bailleui) on Mauna Kea, Island of Hawaiʻi

Palila ( Loxioides bailleui ) are critically endangered Hawaiian honeycreepers specializing on māmane ( Sophora chrysophylla ) seeds and restricted to Mauna Kea volcano on the Island of Hawaiʻi. Recently, the population was estimated to decline by 89% between 1998 and 2021, despite decades of ungulate removal, fence construction, māmane regeneration, fire suppression, and predator control. To inform managers with the most recent update on the status and trends of the Palila population, we analyzed annual bird survey data collected using point-transect distance sampling since 1998, including new annual survey data from 2022, 2023, and 2024. Prior to analysis, we predicted the population trajectory would change between 2021 and 2024 because of continued management actions promoting habitat recovery. We used distance sampling, log-linear regression, and state-space modeling to produce the new estimates and analyze trends across the time series. The 2022 population estimate was 367 to 742 birds (95% confidence interval; point estimate: 545), the lowest in recorded history. The 2023 and 2024 estimates of 374 to 842 birds (point estimate: 596) and 412 to 970 birds (point estimate: 666) were the second and third lowest in our time series, respectively. Our estimates for years before 2022 show population fluctuations between 4000 to 6800 birds from 1998 to 2005, then a steep decline through 2010. For the next decade, abundance fluctuated around 1000 birds, before declining again in 2021 to less than 700 birds. From 1998 to 2024, the population declined by more than 90%, or 205 birds per year, with 100% statistical support for an overall downward trend, despite significant management efforts and research. The greatest threats facing the Palila, if familiar, are not being eliminated swiftly enough to promote their recovery. The currently small and range-limited population is vulnerable to future climate-related events such as drought and fire. Continued monitoring can help to assess the response of Palila to adaptive management actions and changing environmental conditions.

Hawaii↗

USGS2025

Habitat selection by Rocky Mountain Population greater Sandhill Cranes (Antigone canadensis tabida) during spring and autumn migration at a key stopover area

The San Luis Valley (SLV), Colorado is a critical stopover area for Rocky Mountain Population greater Sandhill Cranes ( Antigone canadensis tabida ). During spring and autumn, cranes use crops for foraging and water resources adjacent to foraging areas for roosting and loafing. However, surface water is becoming increasingly limited in the SLV. Understanding the factors that affect use by roosting, loafing, and foraging cranes and where habitat is the most limiting will inform water and habitat management under changing conditions. We used mixed-effects models to determine the effects of habitat variables, ownership, and landcover type on the selection of roosting, loafing, and foraging areas by cranes marked with GPS transmitters (2015–2021). We found that Sandhill Cranes selected for areas with a high amount of water, relatively short vegetation (< 5 m in autumn, < 10 m in spring), close to grain fields (< 5 km), and areas identified as open water for roosting. Loafing Sandhill Cranes also selected for areas with short vegetation and close to grain fields but that had less water and more sandbar and were identified as pastures or wetlands. Although selection was higher for private land overall, we found evidence of avoidance of private lands and a stronger preference for public lands with increasing surface water for roosting in spring. For foraging areas, selection was highest for barley in both seasons, but triticale and other grains had relatively high selection in autumn. Our research confirms the importance of providing roosting and loafing areas on both private and public lands close to foraging areas and provides evidence that roosting and loafing opportunities may be most limited on public lands in the SLV.

Colorado↗

USGS2026

Extrinsic factors similarly affect nest survival of a threatened shorebird in natural and human-created habitats

Knowledge of factors that influence nest survival can inform effective conservation management for imperiled avian species. Habitat availability and quality are common priorities of conservation efforts, and climate and interspecific associations can also affect survival rates. In the lower Platte River system of eastern Nebraska, USA, Piping Plovers ( Charadrius melodus , hereafter plovers) nest on river sandbars and different types of human-created off-river sites (i.e., sand and gravel mines, housing developments, and transitional sites) that are unique within the Northern Great Plains breeding population. However, off-river habitat may not be suitable for plover nesting long-term because of reduced habitat availability on both river sandbars and off-river sites. We evaluated plover nest survival at off-river and sandbar sites using data from 2008 to 2023 (n = 285). In addition, we examined the effects of extreme temperatures, proximity to conspecific and Interior Least Tern ( Sternula antillarum athalassos , hereafter tern) nests, and temporal factors on nest survival. Plover nest survival did not differ between off-river sites and sandbars or amongst different off-river site types. Daily nest survival was 0.9818 (95% CI = 0.9729–0.9878) from 2008 to 2013 (unexclosed; n = 87) and 0.9950 (0.9918–0.9970) from 2014 to 2023 (exclosed; n = 198). Nest survival increased with the proportion of above average temperature days, increased with proximity to neighboring tern nests, and decreased with later nest initiation dates. Therefore, prioritizing early season nests, recognizing the benefits terns provide to plover nest survival, and monitoring the effect of climatic trends may aid future conservation efforts. Finally, as nest survival at off-river sites is comparable to sandbars, the predicted decline of habitat provided at off-river sites may reduce the overall breeding productivity and abundance of plovers in the lower Platte River system with ramifications to broader population viability.

Nebraska↗

USGS2026

Long-term monitoring identifies increase in Henslow’s Sparrow (Centronyx henslowii) abundance following fire management in a North Carolina grassland

Understanding population responses to environmental change is critical for assessing vulnerability, resilience, and habitat management needs. We assessed Henslow’s Sparrow ( Centronyx henslowii ) abundance and breeding productivity in an isolated North Carolina grassland (1149 ha) that transitioned from unmanaged to fire-managed during 2011–2024. Fire management was initiated in 2016, where approximately 1/3 of the grassland is burned annually in late summer on a rotating basis, resulting in a full burn cycle of roughly three years. We used hierarchical distance sampling models to estimate the change in Henslow’s Sparrow abundance before and after fire management from point count data (45–50 locations surveyed annually). Estimated average abundances (i.e., expected number of singing male sparrows per site) significantly increased from 1.387 individuals per survey location pre-management (95% credible interval [CI]: 0.822–2.267) to 3.124 post-management (CI: 2.235–4.385), resulting in annual population sizes ranging from 56 singing male sparrows in 2012 (CI: 36–85), to 411 in 2022 (CI: 342–498). From 2022 to 2023, average brood size was 3.148 (95% confidence interval [CI]: 2.637–3.659) and survival probability for a 24-day nesting cycle was 0.693 (CI: 0.369–0.897). Apparent nesting success was 70–89%, much higher than reported in previous studies (19–62%). Increased abundance post-management indicates that Henslow’s Sparrows are responding positively to the use of prescribed fire, while the estimated rates of breeding productivity indicate the species likely has the capacity to sustain the local population. This study provides baseline information for managers to monitor population status, while laying the foundation to identify regulatory mechanisms and gauge the effectiveness of the current fire management strategy in maintaining an isolated population of Henslow’s Sparrows.

North Carolina↗

USGS2026

King Rails in southeastern Arkansas are majority resident

King Rails ( Rallus elegans ), a declining species of secretive marsh bird, have a mixed migratory strategy, with some individuals migrating and some being year-round residents. Determining the distribution of migratory versus resident King Rails is critical to guiding habitat management and assessing risks to populations. We examined the migratory status of adult King Rails at the Choctaw West Wildlife Management Area in southeastern Arkansas, the only known site in Arkansas with multiple breeding pairs. Of the 23 adult King Rails we tagged in 2022 and 2023, two birds migrated away from the local area, one in each year. One migrated 145 km, and the other 450 km. Our findings suggest that the line between the migratory and resident range of Arkansas King Rails could be north of our site.

Arkansas↗

USGS2003

Amphibian decline: An integrated analysis of multiple stressor effects

Capturing the attention and imagination of the public and the scientific community alike, the mysterious decline in amphibian populations drew scientists and resource managers from ecotoxicology and chemistry, ecology and field biology, conservation biology, and natural resource policy to a SETAC–Johnson Foundation workshop. Facilitating environmental stewardship, increasing capacity of the sciences to explain complex stressors, and educating the public on relationships among communities of all types motivated these experts to address amphibian decline and the role of various stressors in these losses.

Book↗

USGS2014

Freshwater mussels of Florida

An exhaustive guide to all aspects of the freshwater mussel fauna in Florida, Freshwater Mussels of Florida covers the ecology, biology, distribution, and conservation of the many species of bivalve mollusks in the Sunshine State. In the past three decades, researchers, the public, businesses that depend on wildlife, and policy makers have given more attention to the threatened natural diversity of the Southeast, including freshwater mussels. This compendium meets the increasingly urgent need to catalog this imperiled group of aquatic organisms in the United States.

Florida↗

USGS2022

Ignoring species availability biases occupancy estimates in single-scale occupancy models

Most applications of single-scale occupancy models do not differentiate between availability and detectability, even though species availability is rarely equal to one. Species availability can be estimated using multi-scale occupancy models; however, for the practical application of multi-scale occupancy models, it can be unclear what a robust sampling design looks like and what the statistical properties of the multi-scale and single-scale occupancy models are when availability is less than one. Using simulations, we explore the following common questions asked by ecologists during the design phase of a field study: (Q1) what is a robust sampling design for the multi-scale occupancy model when there are a priori expectations of parameter estimates? (Q2) what is a robust sampling design when we have no expectations of parameter estimates? and (Q3) can a single-scale occupancy model with a random effects term adequately absorb the extra heterogeneity produced when availability is less than one and provide reliable estimates of occupancy probability? Our results show that there is a tradeoff between the number of sites and surveys needed to achieve a specified level of acceptable error for occupancy estimates using the multi-scale occupancy model. We also document that when species availability is low (<0.40 on the probability scale), then single-scale occupancy models underestimate occupancy by as much as 0.40 on the probability scale, produce overly precise estimates, and provide poor parameter coverage. This pattern was observed when a random effects term was and was not included in the single-scale occupancy model, suggesting that adding a random-effects term does not adequately absorb the extra heterogeneity produced by the availability process. In contrast, when species availability was high (>0.60), single-scale occupancy models performed similarly to the multi-scale occupancy model. Users can further explore our results and sampling designs across a number of different scenarios using the RShiny app https://gdirenzo.shinyapps.io/multi-scale-occ/ . Our results suggest that unaccounted for availability can lead to underestimating species distributions when using single-scale occupancy models, which can have large implications on inference and prediction, especially for those working in the fields of invasion ecology, disease emergence, and species conservation.

Methods in Ecology and Evolution↗

USGS2016

Governance principles for wildlife conservation in the 21st century

Wildlife conservation is losing ground in the U.S. for many reasons. The net effect is declines in species and habitat. To address this trend, the wildlife conservation institution (i.e., all customs, practices, organizations and agencies, policies, and laws with respect to wildlife) must adapt to contemporary social–ecological conditions. Adaptation could be supported by clear guidelines reflecting contemporary expectations for wildlife governance. We combine elements of public trust thinking and good governance to produce a broad set of wildlife governance principles. These principles represent guidance for ecologically and socially responsible wildlife conservation. They address persistent, systemic problems and, if adopted, will bring the institution into line with modern expectations for governance of public natural resources. Implementation will require changes in values, objectives, and processes of the wildlife conservation institution. These changes may be difficult, but promise improved wildlife conservation outcomes and increased support for conservation. We introduce challenges and opportunities associated with the principles, and encourage dialogue about them among scientists, practitioners, and other leaders in U.S. wildlife conservation. The principles alone will not change the course of conservation for the better, but may be necessary for such change to occur.

Conservation Letters↗

USGS2018

Using spatially‐explicit capture–recapture models to explain variation in seasonal density patterns of sympatric ursids

Understanding how environmental factors interact to determine the abundance and distribution of animals is a primary goal of ecology, and fundamental to the conservation of wildlife populations. Studies of these relationships, however, often assume static environmental conditions, and rarely consider effects of competition with ecologically similar species. In many parts of their shared ranges, grizzly bears Ursus arctos and American black bears U. americanus have nearly complete dietary overlap and share similar life history traits. We therefore tested the hypothesis that density patterns of both bear species would reflect seasonal variation in available resources, with areas of higher primary productivity supporting higher densities of both species. We also hypothesized that interspecific competition would influence seasonal density patterns. Specifically, we predicted that grizzly bear density would be locally reduced due to the ability of black bears to more efficiently exploit patchy food resources such as seasonally abundant fruits. To test our hypotheses, we used detections of 309 grizzly and 597 black bears from two independent genetic sampling methods in spatially‐explicit capture–recapture (SECR) models. Our results suggest grizzly bear density was lower in areas of high black bear density during spring and summer, although intraspecific densities were also important, particularly during the breeding season. Black bears had lower densities in areas of high grizzly bear density in spring; however, density of black bears in early and late summer was best explained by primary productivity. Our results are consistent with the hypothesis that smaller‐bodied, more abundant black bears may influence the density patterns of behaviorally‐dominant grizzly bears through exploitative competition. We also suggest that seasonal variation in resource availability be considered in efforts to relate environmental conditions to animal density.

Montana↗