Search

Annual variation in phenology can have profound effects on the behavior of animals. As climate change advances spring phenology in ecosystems around the globe, it is becoming increasingly important to understand how animals respond to variation in the timing of seasonal events and how their responses may shift in the future. We investigated the influence of spring phenology on the behavior of migratory, barren‐ground caribou (Rangifer tarandus), a species that has evolved to cope with short Arctic summers. Specifically, we examined the effect of spring snow melt and vegetation growth on the current and potential future space‐use patterns of the Porcupine Caribou Herd (PCH), which exhibits large, inter‐annual shifts in their calving and post‐calving distributions across the U.S.–Canadian border. We quantified PCH selection for snow melt and vegetation phenology using machine learning models, determined how selection resulted in annual shifts in space‐use, and then projected future distributions based on climate‐driven phenology models. Caribou exhibited strong, scale‐dependent selection for both snow melt and vegetation growth. During the calving season, caribou selected areas at finer scales where the snow had melted and vegetation was greening, but within broader landscapes that were still brown or snow covered. During the post‐calving season, they selected vegetation with intermediate biomass expected to have high forage quality. Annual variation in spring phenology predicted major shifts in PCH space‐use. In years with early spring phenology, PCH predominately used habitat in Alaska, while in years with late phenology, they spent more time in Yukon. Future climate conditions were projected to advance spring phenology, shifting PCH calving and post‐calving distributions further west into Alaska. Our results demonstrate that caribou selection for habitat in specific phenological stages drive dramatic shifts in annual space‐use patterns, and will likely affect future distributions, underscoring the importance of maintaining sufficient suitable habitat to allow for behavioral plasticity., The Porcupine Caribou Herd spends their summer calving and post‐calving seasons on the Arctic coastal plain of Alaska and Yukon but can exhibit substantial annual shifts in their precise distributions. Our models demonstrated that annual variation in spring snow​ melt and vegetation phenology drove variation in summer range locations. Based on climate projections, the future summer ranges were predicted to shift further west and north into the Alaskan coastal plain due to advancing spring phenology, underscoring the need for sufficient habitat to allow for behavioral adaptation in the changing environment.

Stable isotope data from durable, sequentially grown tissues (e.g. hair, claw, and baleen) is commonly used for modelling dietary niche breadth. The use of tissues grown over multiple months to years, however, has the potential to complicate isotopic niche breadth modelling, as time-averaged stable isotope signals from whole tissues may obscure information available from chronologically resolved stable isotope signals in serially sectioned tissues. We determined if whole samples of brown bear guard hair produced different isotopic niche breadth estimates than those produced from subsampled, serially sectioned samples of the same tissue from the same set of individuals. We sampled guard hair from brown bears (

Variation in life history strategies facilitates the near global distribution of mammals by expanding realized niche width. We investigated physiological plasticity in the spring body composition of adult female brown bears (Ursus arctos) across 4 diverse Alaskan ecosystems. Brown bears are a highly intelligent omnivore with a historic range spanning much of North America, Europe, and Asia. We hypothesized that body mass, fat mass, lean mass, and total caloric content would increase across populations with increasing food resource availability. Throughout their range, brown bears enter a period of torpor during winter months, decreasing their metabolic rate as an adaptation to this period of reduced food availability. They also give birth to and nourish offspring during this time. Due to this specific life history strategy, we further hypothesized that proportional body fat and the proportion of total calories derived from fat would be consistent across populations. Our results supported our first hypothesis: body, fat, and lean masses, and caloric content of bears across populations increased with the quality and abundance of available food. However, the proportional body fat content and proportion of calories from fat differed across populations indicating population-specific strategies to meet the demands of reduced seasonal food availability, offspring production and rearing, and climate as well as some plasticity to respond to environmental change or ecosystem perturbations. Investigations of body condition and energetics benefit from combined assessments of absolute, proportional, and caloric metrics to understand the nuances of brown bear physiological dynamics across and within populations.

A key constraint faced by consumers is achieving a positive energy balance in the face of temporal variation in foraging opportunities. Recent work has shown that spatial heterogeneity in resource phenology can buffer mobile consumers from this constraint by allowing them to track changes in resource availability across space. For example, salmon populations spawn asynchronously across watersheds, causing high-quality foraging opportunities to propagate across the landscape, prolonging the availability of salmon at the regional scale. However, we know little about how individual consumers integrate across phenological variation or the benefits they receive by doing so. Here, we present direct evidence that individual brown bears track spatial variation in salmon phenology. Data from 40 GPS collared brown bears show that bears visited multiple spawning sites in synchrony with the order of spawning phenology. The number of sites used was correlated with the number of days a bear exploited salmon, suggesting the phenological variation in the study area influenced bear access to salmon, a resource which strongly influences bear fitness. Fisheries managers attempting to maximize harvest while maintaining ecosystem function should strive to protect the population diversity that underlies the phenological variation used by wildlife consumers.

Animal consumers track spatial variation in resource phenology (i.e., resource waves) to prolong their access to ephemeral foods. While recent work has revealed how animals move across landscapes to exploit phenological variation among discrete foraging patches, much less is known about how variation nested within patches influences the spatiotemporal pattern of foraging opportunities and the behavior of consumers. Local, within‐patch, variation in phenology influences levels of resource ephemerality and could dictate how frequently consumers must move to continuously exploit a pulsed food source. Here, we explore how within‐site (stream) phenological variation relates to the duration of salmon (Oncorhynchus nerka) runs and its consequences for brown bear (Ursus arctos middendorffi) foraging behavior. We accurately quantified salmon run duration across a large number of spawning streams (21 site‐year combinations). We found that salmon run duration varied threefold among spawning sites and that the source of prolonged runs was within‐site variation in spawning phenology (i.e., the timing of arrival at spawning grounds). Although the estimated reproductive lifespan varied among sites, a simulation suggested that reproductive lifespan has little influence on salmon run duration. Salmon run duration strongly predicted the duration of site occupancy by bears, demonstrating that phenological variation within salmon populations compliments among‐population variation to alleviate time constraints on salmon consumption. To explore whether within‐population variation in salmon phenology was related to spatial variation in habitat conditions (as is the case with among‐population phenological variation), we monitored water temperature, salmon availability, and bear activity across a longitudinal gradient in Connecticut Creek, the study stream with the most prolonged salmon run. Spawn timing varied spatially, occurring first in cold headwater reaches and later in warmer downstream reaches. Patterns of bear presence closely tracked this spawning sequence, suggesting they “surf salmon waves” not only across landscapes but also within spawning sites. However, a coarser analysis across multiple sites suggests phenological variation within salmon populations may not always be spatially structured. Our results demonstrate one way in which local variation in phenology can influence consumer foraging behavior, highlighting the need to understand the causes and consequences of phenological variation at multiple scales.

We collected blood and serum from 155 brown bears (

There is growing interest in the ecological significance of phenological diversity, particularly in how spatially variable resource phenologies (i.e. resource waves) prolong foraging opportunities for mobile consumers. While there is accumulating evidence of consumers moving across landscapes to surf resource waves, there is little data quantifying how phenological tracking influences resource consumption due to the challenge of documenting all the components of this ecological phenomenon (i.e., phenological variation, consumer movement, resource consumption, and consumer fitness). We examined the space use of GPS collared female brown bears to quantify the exploitation of a salmon resource wave by individual bears. We then estimated salmon consumption levels in the same individuals using stable isotope and mercury analyses of hair. We found strong positive relationships between time spent on salmon streams and percent salmon in assimilated diets (R2 = 0.70) and salmon mass consumed (R2 = 0.49). Salmon abundance varied 2.5-fold between study years, yet accounting for salmon abundance did not improve salmon consumption models. Resource abundance generally is viewed as the key variable controlling consumption levels and food web dynamics. However, our results suggest that in intact watersheds of coastal Alaska with abundant salmon runs, interannual variation in salmon abundance likely has less effect on salmon consumption than individual variation in bear foraging behavior. The results complement previous work to demonstrate the importance of phenological variation on bear foraging behavior and fitness.

We collected blood and serum from 155 brown bears (Ursus arctos) inhabiting five locations in Alaska, US during 2013–16 and tested samples for evidence of prior exposure to a suite of bac...

Recruitment of brown bear (Ursus arctos) offspring into a population is the product of initial cub production and subsequent survival and is a critical component of overall population status and trend. We investigated the relationship between maternal body size, body condition, and age (as a surrogate for gained experience) and recruitment of dependent offspring (≥1 yr old) in 4 Alaska, USA (2014–2017), brown bear populations using logistic regression. Body size alone was our top predictor of the presence of offspring and appeared in all top models. Our data suggest that bear size is the primary driver of productivity across all 4 study populations, with larger bears having a greater chance of being observed with offspring. The effect of body condition was likely confounded by the increased energetic costs of supporting cubs through time and had a negative relationship with recruitment. Age (experience) was positively related to recruitment. Understanding the relative importance of body size, body condition, and age on the recruitment of offspring provides insights into life-history trade-offs female bears must manage as they strive to meet the nutritional costs of cub production and rearing, while minimizing risks to themselves and their offspring. Further assessment of long-term longitudinal studies of brown bears that assess the lifetime reproductive output of individuals would be highly informative to further assess the effect of experience on recruitment and to support the management of brown bear populations for recovery, conservation, sustained yield, and ecosystem function.