• Energetic costs of locomotion in bears: is plantigrade locomotion energetically economical?

      Pagano, Anthony M.; Carnahan, Anthony M.; Robbins, Charles T.; Owen, Megan A.; Batson, Tammy; Wagner, Nate; Cutting, Amy; Nicassio-Hiskey, Nicole; Hash, Amy; Williams, Terrie M. (2018)
      Ursids are the largest mammals to retain a plantigrade posture. This primitive posture has been proposed to result in reduced locomotor speed and economy relative to digitigrade and unguligrade species, particularly at high speeds....
    • High-energy, high-fat lifestyle challenges an Arctic apex predator, the polar bear

      Pagano, Anthony M.; Durner, G. M.; Rode, K. D.; Atwood, T. C.; Atkinson, S. N.; Peacock, E.; Costa, D. P.; Owen, Megan A.; Williams, T. M. (2018)
      A demanding lifestyle Polar bears appear to be well adapted to the extreme conditions of their Arctic habitat. Pagano et al., however, show that the energy balance in this harsh environment is narrower than we might expect (see the Perspective by Whiteman). They monitored the behavior and metabolic rates of nine free-ranging polar bears over 2 years....
    • Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity

      Rode, Karyn D.; Wilson, Ryan R.; Douglas, David C.; Muhlenbruch, Vanessa; Atwood, Todd C.; Regehr, Eric V.; Richardson, Evan S.; Pilfold, Nicholas W.; Derocher, Andrew E.; Durner, George M.; et al. (2018)
      The effects of declining Arctic sea ice on local ecosystem productivity are not well understood but have been shown to vary inter-specifically, spatially, and temporally. Because marine mammals occupy upper trophic levels in Arctic food webs, they may be useful indicators for understanding variation in ecosystem productivity. Polar bears (Ursus maritimus) are apex predators that primarily consume benthic and pelagic-feeding ice-associated seals. As such, their productivity integrates sea ice conditions and the ecosystem supporting them. Declining sea ice availability has been linked to negative population effects for polar bears but does not fully explain observed population changes. We examined relationships between spring foraging success of polar bears and sea ice conditions, prey productivity, and general patterns of ecosystem productivity in the Beaufort and Chukchi Seas (CSs). Fasting status (?7 days) was estimated using serum urea and creatinine levels of 1,448 samples collected from 1,177 adult and subadult bears across three subpopulations. Fasting increased in the Beaufort Sea between 1983–1999 and 2000–2016 and was related to an index of ringed seal body condition. This change was concurrent with declines in body condition of polar bears and observed changes in the diet, condition and/or reproduction of four other vertebrate consumers within the food chain. In contrast, fasting declined in CS polar bears between periods and was less common than in the two Beaufort Sea subpopulations consistent with studies demonstrating higher primary productivity and maintenance or improved body condition in polar bears, ringed seals, and bearded seals despite recent sea ice loss in this region. Consistency between regional and temporal variation in spring polar bear fasting and food web productivity suggests that polar bears may be a useful indicator species. Furthermore, our results suggest that spatial and temporal ecological variation is important in affecting upper trophic-level productivity in these marine ecosystems.
    • The seasonal energetic landscape of an apex marine carnivore, the polar bear

      Pagano, Anthony M.; Atwood, Todd C.; Durner, George M.; Williams, Terrie M. (2020)
      …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…. 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 tri-axial accelerometers to identify wild polar bear behaviors

      Pagano, Anthony M.; Rode, K. D.; Cutting, A; Owen, Megan A.; Jensen, S; Ware, J. V.; Robbins, Ct; Durner, Gm; Atwood, Todd C.; Obbard, M. E.; et al. (2017)
      Tri-axial accelerometers have been used to remotely identify the behaviors of a wide range of taxa. Assigning behaviors to accelerometer data often involves the use of captive animals or surrogate species, as their accelerometer signatures are generally assumed to be similar to those of their wild counterparts. However, this has rarely been tested. Validated accelerometer data are needed for polar bears Ursus maritimus to understand how habitat conditions may influence behavior and energy demands. We used accelerometer and water conductivity data to remotely distinguish 10 polar bear behaviors. We calibrated accelerometer and conductivity data collected from collars with behaviors observed from video-recorded captive polar bears and brown bears U. arctos, and with video from camera collars deployed on free-ranging polar bears on sea ice and on land. We used random forest models to predict behaviors and found strong ability to discriminate the most common wild polar bear behaviors using a combination of accelerometer and conductivity sensor data from captive or wild polar bears. In contrast, models using data from captive brown bears failed to reliably distinguish most active behaviors in wild polar bears. Our ability to discriminate behavior was greatest when species- and habitat-specific data from wild individuals were used to train models. Data from captive individuals may be suitable for calibrating accelerometers, but may provide reduced ability to discriminate some behaviors. The accelerometer calibrations developed here provide a method to quantify polar bear behaviors to evaluate the impacts of declines in Arctic sea ice.
    • Validation of mercury tip-switch and accelerometer activity sensors for identifying resting and active behavior in bears

      Ware, Jasmine V.; Rode, Karyn D.; Pagano, Anthony M.; Bromaghin, Jeffrey F.; Robbins, Charles T.; Erlenbach, Joy; Jensen, Shannon; Cutting, Amy; Nicassio-Hiskey, Nicole; Hash, Amy; et al. (2015)
      In this study, we examined the performance of a mercury tip-switch and a tri-axial accelerometer housed in collars to determine whether sensor data can be accurately classified as resting and active behaviors and whether data are comparable for the 2 sensor types. Five captive bears (3 polar [Ursus maritimus] and 2 brown [U. arctos horribilis]) were fitted with a collar specially designed to internally house the sensors. The bears’ behaviors were recorded, classified, and then compared with sensor readings…