Drivers of hibernation: linking food and weather to denning behaviour of grizzly bears
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Climate-induced changes in the phenology of hibernation for bear species could result in altered energy budgets, reduced cub survival and fitness and increased human-bear conflicts. Using 11 years of data, we determined the amount of variation in den entry and den exit dates that could be attributed to sex and reproductive status, weather and berry availability for 15 male and 58 female grizzly bears (Ursus arctos). We estimated berry availability during autumn using a probability surface of berry productivity within the home range of 13 individuals over 3 years. Sex and reproductive status explained 22 and 14 % of the variation in den entry and den exit dates, respectively. Weather did not influence the timing of den entry but berry availability in autumn explained 39 % of the variation observed in den entry, and high berry availability was associated with late den entry. Elevation and spring temperatures, and elevation and winter precipitation, respectively, explained 26 and 21 % of the variation observed in den exit dates. Increasing spring average monthly maximum temperature by 4 °C resulted in bears emerging from dens 10 days earlier and an increase of 1.25 m in snow precipitation delayed den exit by 1 week. We demonstrate that although the phenology of hibernation for grizzly bears depends on sex and reproductive status, den entry appears to be driven by food availability, while den exit is more linked to weather. Extended growing seasons and mild meteorological conditions should result in shorter denning periods for grizzly bears.
Climate change is altering the phenology of spring green-up and the onset of winter, disrupting the seasonal behaviours of species. Climate change can act as an additional strain on threatened populations, especially during energetically demanding periods such as hibernation. We quantified the importance of intrinsic and extrinsic factors including food availability and weather in the hibernation behaviour of grizzly bears. High berry availability was associated with late den entry, while low winter precipitation and high spring temperature resulted in early den exit. We conclude that den entry is more driven by food availability while den exit is more linked to weather. This dichotomy in factors affecting den entry and den exit has implications for the long-term conservation of grizzly bear populations because extended growing seasons and mild meteorological conditions expected under future climate conditions should result in shorter denning periods.
KeywordsBehavioural plasticity Phenology Food availability Den Brown bear Ursus arctos
We thank the Alberta Ecotrust, Y2Y Sarah Baker Memorial Fund, Alberta Conservation Association, Natural Sciences and Engineering Research Council of Canada (NSERC) and fRI Research partners for providing research funds. Université Laval, Centre d’Études Nordiques and NSERC provided funding for conferences to KEP. We thank J. Duval and D. Weins for GIS support; D. Talbot and A.-S. Julien for their help with statistical analyses; R. Théorêt-Gosselin, R. Strong, A. Auger, E. Rogers, C. Curle, T. Larsen, E. Cardinal, P. Stenhouse and A. Stenhouse for collecting field data; and J. Saunders and S. Wotton at Peregrine Helicopters. E. Cardinal, T. Larsen, Ö. E. Can and two anonymous reviewers provided helpful comments and suggestions that improved the manuscript.
Compliance with ethical standards
Capture and handling of grizzly bears were approved by the University of Saskatchewan Animal Care Committee and were in accordance with the American Society of Mammalogists guidelines (Sikes et al. 2011), and all applicable national and institutional guidelines for the care of animals were followed.
Conflict of interest
KEP received a research grant from Alberta Conservation Association Grant in Biodiversity (2009). All authors declare that they have no conflict of interest.
This study was funded by Alberta Ecotrust (2011) and fRI Research Partners.
- Alberta Sustainable Resource Development and Alberta Conservation Association (2010) Status of the grizzly bear (Ursus arctos) in Alberta: update 2010. Wildlife Status Report No. 37 (Update 2010). Alberta Sustainable Resource Development, Edmonton, Alberta, CanadaGoogle Scholar
- Beyer HL (2004) Hawth’s analysis tools for ArcGIS, http://www.spatialecology.com/htools
- Burnham KP, Anderson DR (2002) Model selection and multimodel inference: a practical information-theoretic approach. Springer, New YorkGoogle Scholar
- Craighead FC Jr, Craighead JJ (1972) Data on grizzly bear denning activities and behaviour obtained by using wildlife telemetry. Int C Bear 23:84–106Google Scholar
- ESRI (2008) ArcGIS desktop: release 9.3. Environmental System Research Institute, Redlands, CAGoogle Scholar
- Friebe A, Swenson JE, Sandegren F (2001) Denning chronology of female brown bears in central Sweden. Ursus 12:37–45Google Scholar
- Graham K, Stenhouse GB (2014) Home range, movements, and denning chronology of the grizzly bear (Ursus arctos) in west-central Alberta. Can Field Nat 128:223–233Google Scholar
- Haroldson MA, Ternent MA, Gunther KA, Schwartz CC (2002) Grizzly bear denning chronology and movements in the Greater Yellowstone Ecosystem. Ursus 13:29–37Google Scholar
- IPCC (2013) Climate change 2013: the physical science basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker TF, Qin D, Plattner G-K, Tignor M, Allen SK, Boschung J, Nauels A, Xia Y, Bex V, Midgley PM (eds)]. Cambridge University Press, CambridgeGoogle Scholar
- Laver P (2005) ABODE kernal home range estimation for ArcGIS, using VBA and ArcObjects. User manual (Beta v.2.-7). Department of Fisheries and Wildlife Sciences, Virginia Tech, 149 Cheatham Hall, Blacksburg, VirginiaGoogle Scholar
- Linnell JDC, Swenson JE, Andersen R, Barnes B (2000) How vulnerable are denning bears to disturbance? Wildlife Soc B 28:400–413Google Scholar
- McLellan BN, Servheen C, Huber D (IUCN SSC Bear Specialist Group) (2008) Ursus arctos. The IUCN Red list of threatened species, version 2013.1, www.iucnredlist.org
- Nielsen SE, Cranston J, Stenhouse GB (2009) Identification of priority areas for grizzly bear conservation and recovery in Alberta, Canada. J Conserv Plan 5:38–60Google Scholar
- Noyce KV, Coy PL (1990) Abundance and productivity of bear food species in different forest types of northcentral Minnesota. Int C Bear 8:169–181Google Scholar
- Pasitschniak-Arts M (1993) Ursus arctos. Mamm Species 439:1–10Google Scholar
- SAS Institute Inc (2011) SAS/STAT® 9.3 user’s guide. SAS Institute Inc., Cary, NCGoogle Scholar
- Servheen C, Klaver R (1983) Grizzly bear dens and denning activity in the Mission and Rattlesnake Mountains, Montana. Int C Bear 5:201–207Google Scholar