Sarah E. Jamieson

Do purely capital layers exist among flying birds? Evidence of exogenous contribution to arctic-nesting common eider eggs

The strategy of relying extensively on stored resources for reproduction has been termed capital breeding and is in contrast to income breeding, where needs of reproduction are satisfied by exogenous (dietary) resources. Most species likely fall somewhere between these two extremes, and the position of an organism along this gradient can influence several key life-history traits. Common eiders (Somateria mollissima) are the only flying birds that are still typically considered pure capital breeders, suggesting that they depend exclusively on endogenous reserves to form their eggs and incubate. We investigated the annual and seasonal variation in contributions of endogenous and exogenous resources to egg formation in eiders breeding at the East Bay colony in the Canadian Arctic. We collected prey items along with females and their eggs during various stages of breeding and used two complementary analytical approaches: body reserve dynamics and stable isotope [δ13C, δ15N] mixing models. Indices of protein reserves remained stable from pre-laying to post-laying stages, while lipid reserves declined significantly during laying. Similarly, stable isotope analyses indicated that (1) exogenous nutrients derived from marine invertebrates strongly contributed to the formation of lipid-free egg constituents, and (2) yolk lipids were constituted mostly from endogenous lipids. We also found evidence of seasonal variation in the use of body reserves, with early breeders using proportionally more exogenous proteins to form each egg than late breeders. Based on these results, we reject the hypothesis that eiders are pure capital layers. In these flying birds, the fitness costs of a strict capital breeding strategy, such as temporary loss of flight capability and limitation of clutch and egg size, may outweigh benefits such as a reduction in egg predation rate.

The diet of common eiders wintering in Nuuk, Southwest Greenland

Southwest Greenland provides wintering grounds for 70% (∼460,000) of the northern common eider (Somateria mollissima borealis) population. From 241 gullet samples (esophagus and proventriculus content) collected over three winters (1999–2002) near Nuuk, we identified 39 species consumed by the eiders. In contrast to studies elsewhere, fresh mass of the diet was dominated by soft-bottom species: the bivalve Mya eideri (32.8%) and the polychaete Pectinaria spp. (24.2%). The hard-bottom blue mussel (Mytilus edulis), usually the dominant prey of common eiders, was only the fourth most important diet species (7.5%). Overall, bivalves accounted for 56% of the diet. Twenty-seven prey species were minor foods with aggregate fresh mass of only 5.5%. Diets of males and females were similar, whereas juveniles consumed greater mass of crustaceans and less of bivalves. Diet diversity was higher in mid-winter than late winter, and higher in coastal habitats than in fjords. Within one important wintering area the results indicate that optimal size of blue mussels may be depleted over winter.

The diet of king eiders wintering in Nuuk, Southwest Greenland, with reference to sympatric wintering common eiders

Coastal and offshore waters of Southwest Greenland are internationally important wintering areas for king eiders (Somateria spectabilis) breeding in eastern Canadian Arctic and in northwestern Greenland. This paper presents the first assessment of their winter diet. Based on esophageal-proventricular samples from 26 females (13 juveniles and 13 older birds) and 15 males (11 juveniles and four older birds) collected in 2000–2002 (November–May) in coastal waters of Nuuk, we identified 28 prey species. The diet consisted of almost equal proportions (aggregate fresh mass) of polychaetes, echinoderms, crustaceans and molluscs. The dominant prey species were Pectinaria spp. (26.8%), Strongylocentrotus droebachiensis (18.4%), Mya eideri (11.2%) and Hyas araneus (9.7%). The polychaetes have previously been identified as important prey for eiders in Greenland, but apparently not outside Greenland. Compared with a diet study of common eiders Somateria mollissima from the same wintering area, the king eiders consumed significantly less bivalves and significantly more echinoderms. This difference corresponded with observations that common eiders were feeding in shallow waters, while king eiders were feeding in deeper waters farther from the shore. Benthic surveys are needed to confirm that diet corresponds with prey availability.

An evaluation of methods used to estimate carcass composition of common eiders Somateria mollissima

Abstract To examine how endogenous reserves may influence avian life history, it is often necessary to quantify carcass composition. However, proximate analyses are expensive, time-consuming and difficult to perform under field conditions. Consequently, carcass composition is often estimated from easily measured data. We evaluate methods of estimating carcass composition of the common eider duck Somateria mollissima. We measured, dissected and completed proximate analyses of 92 eiders. Predictive models were derived using multiple regressions of 70 birds, while the remaining 22 were used as an independent test of the models. Each models accuracy was evaluated by comparing estimates against known values of protein and lipids, using root mean square error (RMSE). Abdominal and leg fat pad mass were highly correlated with total lipid (r = 0.92), and body mass was highly correlated with total protein (r = 0.80). Models that used body mass, fat depots and/or muscle group data were the most accurate (lipids adjusted R2 = 0.93, RMSE = 14.60; protein adjusted R2 = 0.74, RMSE = 11.14). By using these equations it is possible, using dissection data, to accurately estimate carcass composition of eiders. If dissection data are not available, one can still estimate carcass composition using equations that require only morphometrics although in our lipid analysis such equations had relatively low accuracy (lipids adjusted R2 = 0.54, RMSE = 32.74).

Endogenous reserve dynamics of northern common eiders wintering in Greenland

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.

Autumn and Winter Diet of Long-Tailed Duck in the Belcher Islands, Nunavut, Canada

-We examined the diet of Long-tailed Ducks (Clangula hyemalis) in the autumn and winter of 1998-99 in the Belcher Islands, Nunavut, Canada. Collections were made in early November before sea ice had formed and in February and March, the time of maximum ice cover. Eight birds collected in the autumn and 19 collected in the winter had food items in the proventriculus/esophagus. For birds collected in the fall, 89% (aggregate wet mass) of the diet consisted of the amphipod Calliopius laeviusculus. The remainder consisted of other smaller amphipods (5%) and sandlance (sandeels, Ammodytes sp.; 6%). In winter, Long-tailed Duck diet consisted of the amphipod Ischyrocerus anquipes (69%), fish eggs (probably sandlance; 24%), sandlance (1%) and other amphipods (5%). Longtailed Duck foraging at the landfast ice floe edge along coasts fed mostly on fish and fish eggs, while those in polynyas among islands fed on amphipods. Consuming soft-bodied prey with high energy densities is likely to allow Longtailed Ducks to successfully winter in the predominately ice-covered Hudson Bay. Received 21 December 2000, accepted 10 January 2001.

Unusual Migration Mortality of King Eiders in Central Baffin Island

-In October 1999, approximately 110 King Eiders (Somateria spectabilis) were found on the ground in the middle of Baffin Island, indicating that these birds had been following an overland migration. The composition of the flock was mixed in both sex (44% female, 56% male) and age of birds (62% hatch year, 38% after hatch year). Approximately 40 birds flew off after resting for six days on the frozen ground. Of the remaining birds that died, predators ate about 15, and 55 were recovered by staff from a local radar site. All eider carcasses carried fat reserves, although there were differences in body mass related to age and sex. Most birds had injuries consistent with crashing into an object at high speed, but in the absence of any obvious vertical obstacles in this region, it appears that this flock flew into the ground during conditions of poor visibility, perhaps facilitated by the formation of cataracts in their eyes. Received 28June 2001, accepted 17 August 2001.