Coping with darkness and low temperatures: foraging strategies in Steller's eiders, Polysticta stelleri, wintering at high latitudes

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Abstract:

To examine how Steller's eiders, Polysticta stelleri, wintering at 70°N cope with adverse winter conditions in terms of darkness and low temperatures, we studied their feeding behaviour during four periods between late autumn and early spring. Steller's eiders were most likely to feed during daylight and twilight, but they also fed during darkness. The incidence of feeding was highest at low tide, and there was a significant interaction between tidal cycle and winter period. Hence, the birds fed more intensively at low tide in midwinter (January) than during the other periods. Air temperatures were between 8 and 10°C lower in midwinter than during the other periods, and during this period the eiders also fed more by means of nondiving techniques (up-ending, surface feeding). The total estimated feeding time was highest in late autumn and midwinter (5.9 and 6.3 h were spent actively feeding, respectively) and lower in late winter and spring (5.1 and 4.6 h, respectively). Thus, as energy requirements increased as a result of low temperatures, Steller's eiders increased their feeding effort, but also reduced feeding costs by reducing diving depth. The results of this study suggest that the Steller's eider is behaviourally well adapted to survive winter at high latitudes at relatively low stress.

Nous avons étudié le comportement de quête de nourriture au cours de quatre périodes de la fin de l'automne au printemps chez des Eiders de Steller, Polysticta stelleri, qui passent l'hiver à 70°N dans le but de déterminer comment ils réussissent à survivre aux températures froides et à l'obscurité. Les oiseaux ont plus tendance à se nourrir durant le jour et au crépuscule, mais ils se nourrissent aussi à l'obscurité. C'est à marée basse que les oiseaux se nourrissent le plus et il y a une interaction significative entre le cycle des marées et la période d'hiver. C'est donc à marée basse au milieu de l'hiver (janvier) que les oiseaux s'alimentent le plus intensément, plus qu'à tout autre moment. A cette période, la température de l'air est de 8 à 10°C plus basse qu'aux autres périodes et, à ce moment, les eiders utilisent plus de tactiques qui ne nécessitent pas de plongée (croupion en l'air, alimentation en surface). Le temps total consacré à l'alimentation est maximal à la fin de l'automne et au milieu de l'hiver (respectivement 5,9 et 6,3 h d'alimentation active) et minimal à la fin de l'hiver et au printemps (5,1 et 4,6 h, respectivement). À mesure que les besoins énergétiques augmentent, donc que les températures baissent, les Eiders de Steller augmentent leurs efforts de quête de nourriture, mais ils réduisent également leurs coûts énergétiques en diminuant la profondeur de leurs plongées. Nos résultats indiquent que l'Eider de Steller est bien adapté par son comportement pour survivre à l'hiver aux latitudes élevées avec relativement peu de stress.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2001

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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