Bears

Contributed Paper
ROOM: CC, Room 26B
SESSION NUMBER: 48
 

1:10PM Quantifying the Influence of Black Bear Use of Human Development on Bear Demographic Rates and Population Dynamics
Heather E. Johnson; David L. Lewis; Stewart W. Breck
Black bear (Ursus americanus) use of human development is increasing in many parts of the country as bears learn to forage on anthropogenic food resources. This behavioral shift has been associated with increases in human-black bear conflicts, and often, the perception that black bear populations are increasing. To better understand the influence of human development on black bear demography, we used global positioning system collars to monitor that habitat-use patterns, body condition, survival and reproductive success of female bears (n=80) in the vicinity of Durango, Colorado, a city that experiences high rates of human-bear conflicts. Using our 6-year dataset, we quantified 1) the influence of black bear use of residential development on different bear fitness traits (body condition, cub productivity, cub survival and adult survival), and 2) their collective effects on bear population growth. After accounting for variation in natural foods and individual bear attributes (e.g., age), known-fate analyses revealed that increased use of residential development by bears was associated with increased body condition and cub productivity, but reduced cub and adult survival. We used our demographic estimates to parameterize a matrix projection model that simulated population growth for bears under a range of development scenarios. Although human development influenced bear demographic rates in unique ways, our model indicated that the costs of reduced cub and adult survival outweighed the benefit of increased cub productivity, resulting in declining population growth with increased bear use of development (95% confidence intervals for population growth were <1 when bears used development ≥11% of the time). As human development continues to expand, it will be increasingly important for wildlife agencies to monitor the dynamics of black bear populations and limit bear foraging for anthropogenic foods in developed landscapes.
1:30PM Long-Term Trends in Body Condition, Growth, and Cub Recruitment in Polar Bears from the Southern Beaufort Sea of Alaska
Todd Atwood; Karyn Rode; George Durner; Kristin Simac; Anthony Pagano
Polar bears (Ursus maritimus) from Alaska’s southern Beaufort Sea (SB) have experienced substantial changes in the seasonal availability of sea ice habitat over the last two decades. These changes have been linked to reduced proportions of ice seals in polar bear diets which, in turn, may be influencing population vital rates. In this study, we investigated potential relationships between the availability of sea ice habitat and polar bear body size, condition, and recruitment over a period spanning four decades. Since 1982, the length of the annual open-water season (i.e., number of days per calendar year with ice cover <50%) in the SB has increased at a rate of ~15 days decade-1. Indices of body size, condition, and recruitment declined over time and were smaller following years with longer open-water seasons. Additionally, the percent of adult females fasting during spring increased by 40% from 1982-1999 to 2000-2016. Collectively, these findings suggest that nutritional limitations associated with declining sea ice habitat are associated with reductions in body condition and reproduction in SB polar bears.
1:50PM Terrestrial Habitat Selection By Adult Female Polar Bears in Western Hudson Bay, Canada
Alex M.C. Beatty; Andrew E. Derocher; Nicholas J. Lunn
The Western Hudson Bay polar bear (Ursus maritimus) population in the Canadian Arctic spends ice-free summer months on land. While onshore, they move infrequently to conserve energy. As freeze-up advances, bears migrate from land to newly forming sea-ice. Climate change is altering sea ice phenology, which forces polar bears to spend an increasing amount of time on land. Therefore, understanding the terrestrial habitats utilized by polar bears may become increasingly important for conservation planning. The objective of this research was to assess population and seasonal habitat selection of polar bears when on land during the ice-free period. Global positioning system (GPS) collars on 122 adult female bears provided >50,000 locations that were used to assess terrestrial habitat use during July through January, 2004-2017. Land cover classes were determined using a high resolution terrestrial ecosystem map that identified 24 habitat types. Resource selection functions (RSFs) with Akaike Information Criterion (AIC) model selection evaluated terrestrial habitat selection to predict relative probability of use of different habitats within Wapusk National Park, Manitoba, Canada. Adult female polar bears on land prefer riparian areas and freshwater ponds while avoiding the Hudson Bay coast. Selection for riparian areas during the ice-free period provide important water sources, while adult females with cubs avoid the coast to decrease the risk of infanticide by adult male bears. Seasonal selection indicates riparian and freshwater ponds are preferred throughout the on-land period. While female polar bears with cubs typically avoid the Hudson Bay coast, bears select for the coast as they migrate on and off land.
2:10PM Habitat Selection Patterns of Polar Bears at the Southernmost Extent of Their Distribution
Joseph Northrup; Kevin Middel; Erica Newton; Martyn Obbard; Gregory Thiemann
Climate change is predicted to fundamentally alter habitat for a range of species. Polar bears (Ursus maritimus) offer perhaps the starkest example of this as their primary habitat (sea-ice) is predicted to disappear entirely from large portions of their range. Examining the habitat selection patterns of polar bears can provide insight to preferred sea-ice characteristics which can be used to predict changes in polar bear habitat. This information is critical for understanding future impacts to the species and for assessing the potential for bears to cope with changing sea-ice conditions. With this in mind, our objectives were to 1) characterize the on-ice habitat selection patterns of polar bears relative to sea-ice characteristics in James and Hudson Bays, the southernmost distribution of polar bears globally, and 2) assess seasonal and individual variation in these patterns relative to sea-ice dynamics. We deployed satellite-linked global positioning system radio collars on 25 female polar bears on land adjacent to James Bay between 2012 and 2015. We examined the fine-scale habitat selection patterns of bears using movement-based resource selection functions in a hierarchical framework, allowing conjoint assessment of individual and group-level patterns of habitat selection. Using the individual results, we examined how habitat selection patterns varied relative to ice dynamics at a broader scale. These results offer insight to how sea-ice changes at the scale of the subpopulation will dictate the behavior of polar bears. This information can be used to predict how polar bears will respond to continuing changes in their sea-ice habitat.
12:50PM Scale-Dependent Home Range Optimality for a Solitary Omnivore, American Black Bear
Mariela Gantchoff; Dean Beyer; Guiming Wang; Jerrold Belant
Studying how species modify their space use in response to landscape structure is useful for managing species like American black bear (Ursus americanus), which are currently recolonizing portions of the USA after major range contractions. We evaluated support for three hypotheses: (1) home range location on a landscape will correspond with high vegetation productivity, (2) increasing forest fragmentation will result in larger ranges, and (3) increasing proportion of forest and/or mean vegetation productivity will result in smaller ranges. We used telemetry data from Michigan (2009-2015), Missouri (2010-2016) and Mississippi (2008-2017), USA. Annual ranges excluded winter, and seasonal ranges were separated into spring, summer, and fall. Data included 143 bears (80 females, 63 males), resulting in 97 annual and 538 seasonal ranges. We used generalized linear mixed models to evaluate productivity (Normalized Difference Vegetation Index) selection, and range size (km2) variation of individuals. At the annual scale, black bears consistently selected areas with greater vegetation productivity than the surrounding landscape; yet selection weakened seasonally. Opposite to our prediction, we found that increasing fragmentation of forest patches consistently resulted in smaller ranges; forest edges themselves might provide greater or more diverse foods for bears. We supported our prediction that ranges with a greater proportion of forest would be smaller, likely reflecting an increase in resources which could reduce movements, yet there was no support for more productive ranges also being smaller. Black bears displayed a scale-dependent space use strategy: at larger spatial and temporal scales, productivity acted as the strongest limiting factor and energy maximizing was the dominant strategy, while an area minimizing strategy was exhibited seasonally. By quantifying black bear space use across different areas, over time, and among and within individuals, we revealed consistent responses to environmental conditions while highlighting the plasticity of this flexible omnivore.

 

Contributed Paper
Location: Cleveland CC Date: October 9, 2018 Time: 12:50 pm - 2:30 pm