Habitat degradation affects the summer activity of polar bears

Ware, Jasmine V.; Rode, Karyn D.; Bromaghin, Jeffrey F.; Douglas, David C.; Wilson, Ryan R.; Regehr, Eric V.; Amstrup, Steven C.; Durner, George M.; Pagano, Anthony M.; Olson, Jay; Robbins, Charles T.; Jansen, Heiko T.

doi:10.1007/s00442-017-3839-y

Cited by 62 publications

(47 citation statements)

References 73 publications

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“…Our results are also consistent with Ware et al (), who found activity in SB polar bears declined when using sea ice off the continental shelf. We found month to be a better predictor of energy expenditure than sea ice concentration, as month likely reflects a combination of both seasonal changes in sea ice concentration and variability in prey accessibility (Ware et al ). Both factors would be expected to influence polar bear activity and energy expenditure.…”

Section: Discussionsupporting

confidence: 93%

“…This pattern is also consistent with the decline in energy expenditure we found in August and September as bears increasingly used habitat off the continental shelf or on land. In polar bears, activity rates are thought to increase in response to the availability of seal prey (Messier et al , Ware et al ); our findings support this concept. Our results are also consistent with Ware et al (), who found activity in SB polar bears declined when using sea ice off the continental shelf.…”

Section: Discussionsupporting

confidence: 86%

“…In polar bears, activity rates are thought to increase in response to the availability of seal prey (Messier et al , Ware et al ); our findings support this concept. Our results are also consistent with Ware et al (), who found activity in SB polar bears declined when using sea ice off the continental shelf. We found month to be a better predictor of energy expenditure than sea ice concentration, as month likely reflects a combination of both seasonal changes in sea ice concentration and variability in prey accessibility (Ware et al ).…”

Section: Discussionsupporting

confidence: 86%

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The seasonal energetic landscape of an apex marine carnivore, the polar bear

Pagano

Atwood

Durner

et al. 2020

Ecology

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Divergent movement strategies have enabled wildlife populations to adapt to environmental change. In recent decades, the Southern Beaufort Sea subpopulation of polar bears (Ursus maritimus) has developed a divergent movement strategy in response to diminishing sea ice where the majority of the subpopulation (73–85%) stays on the sea ice in summer and the remaining bears move to land. Although declines in sea ice are generally considered a challenge to energy balance in polar bears residing in some regions of the Arctic, little quantitative data exists concerning the seasonal energy expenditures of this apex marine carnivore. We used GPS satellite collars with tri‐axial accelerometers and conductivity sensors to measure the location, behavior, and energy expenditure of five adult female polar bears in the southern Beaufort Sea across seasons of sea ice breakup and minimum extent. Using a Bayesian mixed‐effects model, we found that energy expenditure was influenced by month, ocean depth, and habitat type (sea ice or land). Total energy expenditure from May through September ranged from 37.7 to 47.2 mJ/kg for individual bears. Bears that moved to land expended 7% more energy on average from May through September than bears that remained on the receding sea ice. In August, when bears were moving from the sea ice to land or moving north with the receding pack ice, bears that moved to land spent 7% more time swimming and expended 22% more energy. This means the immediate cost of moving to land exceeded the cost of remaining on the receding summer pack ice. These findings suggest a physiological reason why the majority of the Southern Beaufort Sea subpopulation continues to inhabit a diminishing summer ice platform. However, bears that moved to land spent 29% more time in preferred hunting habitats over the continental shelf than bears that remained on the sea ice. Bears on land also had access to subsistence‐harvested bowhead whale carcasses. Hence, our findings indicate there may be a greater overall energetic benefit to move to land in this region, which suggests that the use of the diminishing summer sea ice may be functioning as an ecological trap.

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Section: Discussionsupporting

confidence: 93%

Section: Discussionsupporting

confidence: 86%

Section: Discussionsupporting

confidence: 86%

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The seasonal energetic landscape of an apex marine carnivore, the polar bear

Pagano

Atwood

Durner

et al. 2020

Ecology

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“…The largest decrease occurred during late winter–early spring (February/March–April/May) in all subpopulations and was likely a result of low prey availability (Stirling & Øritsland, ). Consistent with reduced foraging success, polar bears significantly reduce movement rates and activity levels from late summer through to winter (Ferguson et al, ; Laidre et al, ; Messier, Taylor, & Ramsay, ; Ware et al, ), which may help conserve stored energy during periods of low prey accessibility.…”

Section: Discussionmentioning

confidence: 99%

Correlates of seasonal change in the body condition of an Arctic top predator

Galicia

Thiemann

Dyck

2019

Global Change Biology

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Climate‐driven sea ice loss has led to changes in the timing of key biological events in the Arctic, however, the consequences and rate of these changes remain largely unknown. Polar bears (Ursus maritimus) undergo seasonal changes in energy stores in relation to foraging opportunities and habitat conditions. Declining sea ice has been linked to reduced body condition in some subpopulations, however, the specific timing and duration of the feeding period when bears acquire most of their energy stores and its relationship to the timing of ice break‐up is poorly understood. We used community‐based sampling to investigate seasonality in body condition (energy stores) of polar bears in Nunavut, Canada, and examined the influence of sea ice variables. We used adipose tissue lipid content as an index of body condition for 1,206 polar bears harvested from 2010–2017 across five subpopulations with varying seasonal ice conditions: Baffin Bay (October–August), Davis Strait and Foxe Basin (year‐round), Gulf of Boothia and Lancaster Sound (August–May). Similar seasonal patterns were found in body condition across subpopulations with bears at their nadir of condition in the spring, followed by fat accumulation past break‐up date and subsequent peak body condition in autumn, indicating that bears are actively foraging in late spring and early summer. Late season feeding implies that even minor advances in the timing of break‐up may have detrimental effects on foraging opportunities, body condition, and subsequent reproduction and survival. The magnitude of seasonal changes in body condition varied across the study area, presumably driven by local environmental conditions. Our results demonstrate how community‐based monitoring of polar bears can reveal population‐level responses to climate warming in advance of detectable demographic change. Our data on the seasonal timing of polar bear foraging and energy storage should inform predictive models of the effects of climate‐mediated sea ice loss.

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“…For example, polar bears have been observed attacking walruses hauled out on the coast in the fall, and Alaskan hunters have reported the consumption of spotted seals in winter (Voorhees, Sparks, Huntington, & Rode, ). The changing phenology of Arctic sea ice (Serreze, Crawford, Stroeve, Barrett, & Woodgate, ) is altering polar bear's behavior and habitat selection (Rode et al., ; Ware et al., ) and, combined with the ecosystem response to ice loss (e.g., Feng, Ji, Campbell, Ashjian, & Zhang, ; Moore, ), may be shifting the composition of prey species available to polar bears (e.g., Beatty et al., ; Galicia, Thiemann, Dyck, Ferguson, & Higdon, ).…”

Section: Discussionmentioning

confidence: 99%

Simultaneous estimation of diet composition and calibration coefficients with fatty acid signature data

Bromaghin

Budge

Thiemann

et al. 2017

Ecology and Evolution

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Knowledge of animal diets provides essential insights into their life history and ecology, although diet estimation is challenging and remains an active area of research. Quantitative fatty acid signature analysis (QFASA) has become a popular method of estimating diet composition, especially for marine species. A primary assumption of QFASA is that constants called calibration coefficients, which account for the differential metabolism of individual fatty acids, are known. In practice, however, calibration coefficients are not known, but rather have been estimated in feeding trials with captive animals of a limited number of model species. The impossibility of verifying the accuracy of feeding trial derived calibration coefficients to estimate the diets of wild animals is a foundational problem with QFASA that has generated considerable criticism. We present a new model that allows simultaneous estimation of diet composition and calibration coefficients based only on fatty acid signature samples from wild predators and potential prey. Our model performed almost flawlessly in four tests with constructed examples, estimating both diet proportions and calibration coefficients with essentially no error. We also applied the model to data from Chukchi Sea polar bears, obtaining diet estimates that were more diverse than estimates conditioned on feeding trial calibration coefficients. Our model avoids bias in diet estimates caused by conditioning on inaccurate calibration coefficients, invalidates the primary criticism of QFASA, eliminates the need to conduct feeding trials solely for diet estimation, and consequently expands the utility of fatty acid data to investigate aspects of ecology linked to animal diets.

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Habitat degradation affects the summer activity of polar bears

Cited by 62 publications

References 73 publications

The seasonal energetic landscape of an apex marine carnivore, the polar bear

The seasonal energetic landscape of an apex marine carnivore, the polar bear

Correlates of seasonal change in the body condition of an Arctic top predator

Simultaneous estimation of diet composition and calibration coefficients with fatty acid signature data

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