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Consumption of salmon by Alaskan brown bears: a trade-off between nutritional requirements and the risk of infanticide?

  • Behavioual Ecology
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Abstract

The risk of infanticide may alter foraging decisions made by females, which otherwise would have been based on nutritional requirements and forage quality and availability. In systems where meat resources are spatially aggregated in late summer and fall, female brown bears ( Ursus arctos) would be faced with a trade-off situation. The need of reproductive females to accumulate adequate fat stores would likely result in a decision to frequent salmon streams and consume the protein- and lipid-rich spawning salmon. In contrast, aggregations of bears along salmon streams would create conditions of high risk of infanticide. We investigated consumption of salmon by brown bears on Admiralty and Chichagof Islands in Southeast Alaska from 1982 to 2000 using stable isotope analysis and radiotelemetry. While nearly all males (22 of 23) consumed relatively large amounts of salmon (i.e., >10% relative contribution to seasonal diet), not all females ( n =56) did so. Five of 26 females for which we had reproductive data, occupied home ranges that had no access to salmon and thus did not consume salmon when they were mated or accompanied by young. Of females that had access to salmon streams ( n =21), all mated individuals ( n =16) had δ15N values indicative of salmon consumption. In contrast, 4 out of 16 females with cubs avoided consuming salmon altogether, and of the other 12, 3 consumed less salmon than they did when they were mated. For 11 of 21 females with access to salmon streams we had data encompassing both reproductive states. Five of those altered foraging strategies and exhibited significantly lower values of δ15N when accompanied by young than when mated, while 6 did not. Radiotelemetry data indicated that females with spring cubs were found, on average, further away from streams during the spawning season compared with females with no young, but both did not differ from males and females with yearlings and 2-year-olds. Females with young that avoided salmon streams were significantly lighter indicating that female choice to avoid consumption of salmon carries a cost that may translate to lower female or cub survivorship. The role of the social hierarchy of males and females, mating history, and paternity in affecting the risk of infanticide and foraging decisions of female brown bears merit further investigation.

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Acknowledgements

This paper is dedicated to the memory of Dr. Malcolm Ramsay. Malcolm Ramsay (Professor at the University of Saskatchewan, Saskatoon) spent decades studying the ecology and behavior of polar bears in the Canadian high Arctic. We had the pleasure of discussing our ideas on trade-offs encountered by bears on numerous occasions. Malcolm provided insightful comments and constructive criticism to our work. On 20 May 2000, Malcolm Ramsay died in a helicopter crash during research out of Resolute Bay, Nunavut. The Southeast Alaska brown bear research program was initiated by J. Schoen. His foresight in collecting and archiving samples during the early years of the project made it possible to follow females through different reproductive phases and deserves our highest appreciation and gratitude. We appreciate the assistance of numerous ADF&G staff with field-work. L. Bennett and other fixed-wing pilots provided safe flying, and the long-term skilled assistance of helicopter pilot B. Englebrecht was instrumental in obtaining many of the samples used in this paper. G.V. Hilderbrand, S.D. Farley, C.T. Robbins, G.M. Blundell, and R.W. Flynn provided insightful discussions on bear ecology and stable isotope analysis. R.W. Flynn and T.V. Schumacher assisted in GIS analyses. We thank C. Restrepo for assistance in sample preparation in the laboratory. N. Haubenstock, P. Rivera, and T. Howe performed the stable isotope analysis. G.V. Hilderbrand and D. Esler, M. Festa-Bianchet and 3 anonymous reviewer provided insightful comments on earlier versions of the manuscript. This study was funded primarily by the Alaska Department of Fish and Game (ADF&G) and the Federal Aid in Wildlife Restoration Program (Studies 4.17 and 4.26). The Alaska Region of the U.S. Forest Service provided financial assistance from 1989 to 93 for the Chichagof Island portion of the study and we appreciate the support from the Hoonah Ranger District.

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  1. Department of Zoology and Physiology, University of Wyoming, P.O. Box 3166, Laramie, WY, 82071, USA

    Merav Ben-David

  2. Division of Wildlife Conservation, Alaska Department of Fish and Game, Douglas, AK, 99824, USA

    Kimberly Titus & LaVern R. Beier

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  1. Merav Ben-David
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Correspondence to Merav Ben-David.

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Ben-David, M., Titus, K. & Beier, L.R. Consumption of salmon by Alaskan brown bears: a trade-off between nutritional requirements and the risk of infanticide?. Oecologia 138, 465–474 (2004). https://doi.org/10.1007/s00442-003-1442-x

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