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Bite rates in Rocky Mountain bighorn sheep (Ovis canadensis): effects of season, age, sex and reproductive status

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Abstract

We investigated the effects of vegetation biomass, crude protein content of consumed forage, age, sex and reproductive status on bite rates in Rocky Mountain bighorn sheep. We expected higher bite rates and vigilance in lactating females with young and higher bite rates in young growing individuals, than in non-reproducing females or rams. Lactating ewes had higher bite rates than yeld ewes and than subadult or adult rams. Subadult rams had higher bite rates than adult rams or yeld ewes. On recently burned grassland in spring, however, rams had a higher bite rate than adult females, while the contrary was true on control plots and on the burned plots in autumn. Bite rates declined for both ewes and rams from April to September and varied from year to year. While rams of different ages had significantly different bite rates, there was no effect of age on bite rates for ewes. There was no correlation between bite rates and available total biomass or biomass of live vegetation, or the numbers of steps taken while foraging for either ewes or rams. Adult rams had a lower vigilance rate than adult ewes, and vigilance decreased with increasing bite rates for all sheep. Bite rates in bighorn sheep vary greatly according to age, season and vegetation structure. An increase in bite rates during the forage growing season may compensate for higher energy demands during lactation and growth. There is a potential trade-off between foraging and vigilance as vigilance decreased with increasing bite rates.

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Acknowledgements

We thank D. Heynen, R. Fankhauser, S. Ruckstuhl, C. Schütz, S. Rebel, J. Roberge, A. Lüscher, A. Hämmerli, Y. Teuschl and M. -C. Kamke for their help in the field; K. Livingston and B. Wuth (fire specialists, Rocky Mountain House), K. Orich and his crew (Forestry department, Turner Valley) for the prescribed burning; and G. Pomerleau, C. Beaudoin, L.-M. Thériault and B. Mercier for laboratory analyses. Thanks to P. Neuhaus and Sandro Lovari for critical comments on an earlier draft of this manuscript and Tim Coulson, Giacomo Tavecchia and Byron Morgan for statistical advice. Financial support was provided by a Challenge Grant in Biodiversity from the University of Alberta, Department of Biological Sciences and financed through the Alberta Department of Environmental Protection, Fish and Wildlife Trust Fund to K.E. Ruckstuhl; the Alberta Sports, Recreation, Parks and Wildlife Foundation; Alberta Conservation Association; and the Natural Sciences and Engineering Research Council of Canada (NSERC). This manuscript was written while K.E. Ruckstuhl was at the University of Cambridge and financed by an NSERC postdoctoral fellowship and a UK Millennium award. This is a contribution of the Groupe de recherche en écologie, nutrition et énergétique, Département de biologie, Université de Sherbrooke. Our experiments and treatment of animals comply with the current laws of Canada.

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  1. Groupe de recherche en écologie nutrition et énergétique, Département de biologie, Université de Sherbrooke, Sherbrooke, PQ, J1K 2R1, Canada

    K. E. Ruckstuhl & M. Festa-Bianchet

  2. Department of Zoology, LARG, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK

    K. E. Ruckstuhl

  3. Natural Resources Service, Suite 201, 800 Railway Ave., Canmore, AB, T1W 1P1, Canada

    J. T. Jorgenson

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  1. K. E. Ruckstuhl
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  2. M. Festa-Bianchet
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  3. J. T. Jorgenson
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Correspondence to K. E. Ruckstuhl.

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Communicated by A. Cockburn

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Ruckstuhl, K.E., Festa-Bianchet, M. & Jorgenson, J.T. Bite rates in Rocky Mountain bighorn sheep (Ovis canadensis): effects of season, age, sex and reproductive status. Behav Ecol Sociobiol 54, 167–173 (2003). https://doi.org/10.1007/s00265-003-0615-2

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