BRANTA — Sarah Emily Jamieson
Endogenous reserve dynamics of Northern Common Eiders (Somateria mollissima borealis) wintering in Greenland
Institution: University of New Brunswick, Canada
Supervisors: Grant Gilchrist, Tony Diamond
Details: MSc 2003 (Completed)
Address: Museum of New Zealand Te Papa Tongarewa (Jan 2013) Email
Subject Keywords: Arctic, body condition, energy stores, lipids, protein, strategy
Species Keywords: Common Eider Somateria mollissma borealis
Levels of endogenous energy reserves have been shown to influence both survival and reproduction of many waterfowl species, but little is known about the endogenous reserve dynamics of many species during winter. This is particularly true among species that winter in polar regions where fat reserves may be especially important for survival. In this study, I investigated the effects of sex, age, and season on the carcass composition of Northern Common Eiders (Somateria mollissima borealis) wintering in southwest Greenland during the winters of 1999-2000, 2000-2001, and 2001-2002. Seven hundred and forty-eight eiders were collected in Greenland as part of an Aboriginal harvest between the months of November and May and an additional 99 were collected while staging during migration near Cape Dorset, Nunavut, Canada in April and May. Eiders were sexed according to their syrinx morphology and aged by bursa of Fabricius length and plumage. Two age groups were analysed: adults (>3yr) and juveniles (<1yr).
A sub-sample of 92 eiders underwent total carcass analysis for protein, lipid, and ash. Using these data I evaluated methods of estimating carcass composition of Northern Common Eiders. Predictive models were derived with multiple regressions using 70 of these birds, and the remaining 22 were used as an independent test of the models. The accuracy of each model was evaluated by comparing estimates against known values of protein and lipids from each carcass, using root mean square error of prediction (RMSE). Models that included body mass, weights of individual fat depots and/or muscle groups were the most accurate (lipids Radj2= 0.93, RMSE= 14.60; protein Radj2= 0.74, RMSE= 11.14). Two previously published equations and models derived using only external morphological variables had relatively low accuracy. By using equations derived in this study it is possible, using dissection data, to accurately estimate carcass composition of eiders in winter, although if dissection data are not available it is still possible to get an indication of body condition from equations requiring only body mass and size data. With the most accurate models, I estimated the carcass composition of the remaining 755 birds included in this study.
For all analyses that related carcass composition to sex and age classes, I controlled for structural body size using principal components analysis. During all winters, adults carried more lipids and protein than juveniles. Among both adults and juveniles, males and females had similar fat levels but males carried more protein. There was no seasonal variation in protein content. There was little variation in lipid content, although there was a general tendency for a mid winter peak in lipid storage, and for juveniles to lose lipids throughout the winter. There was little relation between lipid reserve levels and ambient temperature, or hunting disturbance intensity, although there was some support for an inverse relationship between photoperiod and juvenile fat reserves. Birds collected during spring migration had higher fat levels but lower protein levels than their conspecifics collected concurrently on the wintering grounds in Greenland.
I propose that because of their similar carcass compositions, male and female eiders are equally capable of dealing with nutritional stress, and that juvenile birds, because of their smaller endogenous reserves, are more prone to stress than adults. However, my findings suggest that during the period of this study eiders wintering in Greenland did not experience large-scale nutritional stress.
Jamieson, S.E., Gilchrist, H.G., Merkel, F,. Diamond, A.W. & Falk, K.. 2006. Endogenous reserve dynamics of Northern Common Eiders wintering in Greenland. Polar Biology 29: 585-594. View paper
Jamieson, S.E., Gilchrist, H.G., Merkel, F., Falk, K. & Diamond, A.W.. 2006. An evaluation of methods used to estimate carcass composition of Common Eiders Somateria mollissima. Wildlife Biology 12: 219-226.