Seasonal range size in relation to reproductive strategies in brown bears Ursus arctos

Authors

  • Bjørn Dahle,

    Corresponding author
    1. Department of Zoology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway and †Department of Biology and Nature Conservation, Agricultural University of Norway, Post Box 5014, N-1432 Ås, Norway and Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway
      *Correspondence and present address: Bjørn Dahle, Department of Biology and Nature Conservation, Agricultural University of Norway, Post Box 5014, N-1432 Ås, Norway. Tel. +47 64948516/67903118. E-mail: bjorn.dahle@ibn.nlh.no
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  • and * Jon E. Swenson

    1. Department of Zoology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway and †Department of Biology and Nature Conservation, Agricultural University of Norway, Post Box 5014, N-1432 Ås, Norway and Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway
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*Correspondence and present address: Bjørn Dahle, Department of Biology and Nature Conservation, Agricultural University of Norway, Post Box 5014, N-1432 Ås, Norway. Tel. +47 64948516/67903118. E-mail: bjorn.dahle@ibn.nlh.no

Summary

  • 1Data on seasonal ranges of 93 radio-collared adult brown bears (Ursus arctos) were used to test hypotheses explaining variation in range size in relation to male and female reproductive strategies.
  • 2Both males and oestrous females used large ranges in the mating season, but decreased their ranges after the mating season. These results suggested that both sexes in this species roam to mate, because the results could not be explained by a seasonal change in food availability nor by increased foraging movements of oestrous females to replenish body reserves after previous cub raising.
  • 3Females with cubs-of-the-year (cubs) restricted their range size in the mating season and increased their ranges in the post-mating season. This finding suggests that females with cubs restricted their ranges to avoid contact with infanticidal males, an important cause of cub mortality, because the proposed alternative explanation − limited mobility of small cubs − was unable to explain the small size of mating season ranges.
  • 4Our results suggest that range size in females is influenced by sexually selected infanticide, selecting for large mating season ranges and multiple mating in oestrous females to hide paternity and for restricted mating season ranges in females with cubs to avoid infanticidal males.
  • 5To our knowledge, we are the first to report a significant relationship between seasonal range size and reproductive status in female brown bears and the first to report an effect of oestrus on seasonal range size in female carnivores.

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