Endogenous reserve dynamics of northern common eiders wintering in Greenland

Simon Fraser University Biological Sciences 8888 University Drive V5A 1S6 Burnaby BC Canada
Polar Biology (Impact Factor: 2.01). 01/2006; 29(7):585-594. DOI: 10.1007/s00300-005-0093-2

ABSTRACT Endogenous reserves influence both survival and reproduction of many waterfowl species, but little is known about reserve levels of most species during the nonbreeding season, particularly those wintering at high latitudes. We investigated whether age, sex, and season were related to carcass composition of northern common eiders (Somateria mollissima borealis) wintering in southwest Greenland during 1999–2002. Adults carried more lipid and protein than juveniles during all winters. Among both age classes, males and females had similar fat levels but males carried slightly more protein. There was no dramatic seasonal variation in lipid or protein content. This suggests that during the period of this study, these eiders did not experience large-scale nutritional shortfalls. As predicted, Greenlandic eiders carried more lipid reserves than eider populations wintering in more temperate environments. Contrary to prediction, there was little relation between reserve levels and photoperiod, ambient temperature, or hunting disturbance intensity. Our results suggest that both sexes are equally capable of dealing with nutritional deficits, and that juvenile birds are more prone to nutritional stress as evidenced by their consistently poorer body condition.

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    ABSTRACT: The number of common eiders (Somateria mollissima borealis) in west Greenland declined dramatically during the twentieth century, supposedly because of human activities. However, their sensitivity to alternative drivers of variation, such as climate conditions, diseases or food availability, remains unstudied. In this study, we describe prey availability and assess the trophic coupling between eiders and their macrobenthic prey in a shallow inlet, Nipisat Sound; a key wintering habitat in the south-west Greenland Open Water Area. Macrobenthic species abundance and biomass were studied, and annual production was estimated by an empirical model, including environmental characteristics, fauna composition and individual biomass. In spring 2008, average macrozoobenthic abundance and biomass were 6,912indm−2 and 28.4g ash-free dry mass (AFDM)m−2 (647kJm−2), respectively. Annual production was estimated at 13.9g AFDM m−2year−1 (317kJm−2year−1). During the winters of 2008–2010, we monitored the number of common eiders (S. mollissima borealis) and king eiders (Somateria spectabilis) and observed a distinct peak in abundance during winter with up to 15.000 birds in Nipisat Sound. Based on physiological costs of different activities in combination with the observed behavioural pattern, we obtained an estimate of the energy required for eiders to balance their costs of living, which amounted to 58% of the estimated total annual production of macrobenthos in Nipisat Sound. This result suggests that eider predation affects macrobenthic species composition and biomass and demonstrates the potential importance of variations in prey availability for the population dynamics of eiders in Greenland. Keywords Somateria mollissima – Somateria spectabilis –Arctic–Nuuk–Godthaabsfjord–Nipisat sound–Production–Infauna–Benthos– Mya
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    ABSTRACT: Body size affects foraging and forage intake rates directly via energetic processes and indirectly through interactions with social status and social behaviour. Ambient temperature has a relatively greater effect on the energetics of smaller species, which also generally are more vulnerable to predator attacks than are larger species. We examined variability in an index of intake rates and an index of alertness in Lesser Snow Geese Chen caerulescens caerulescens and Ross's Geese Chen rossii wintering in southwest Louisiana. Specifically we examined variation in these response variables that could be attributed to species, age, family size and ambient temperature. We hypothesized that the smaller Ross's Geese would spend relatively more time feeding, exhibit relatively higher peck rates, spend more time alert or raise their heads up from feeding more frequently, and would respond to declining temperatures by increasing their proportion of time spent feeding. As predicted, we found that Ross's Geese spent more time feeding than did Snow Geese and had slightly higher peck rates than Snow Geese in one of two winters. Ross's Geese spent more time alert than did Snow Geese in one winter, but alert rates differed by family size, independent of species, in contrast to our prediction. In one winter, time spent foraging and walking was inversely related to average daily temperature, but both varied independently of species. Effects of age and family size on time budgets were generally independent of species and in accordance with previous studies. We conclude that body size is a key variable influencing time spent feeding in Ross's Geese, which may require a high time spent feeding at the expense of other activities.
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