Eider

Abstract: -In 1982 we studied weight loss, changes in body composition, and energy expenditure in breeding female Common Eiders (Somateria mollissima borealis) in Svalbard, Norway. Feeding ceased during laying and incubation. From prelaying to hatching, total weight declined by 46.4%, lipid by 81.4%, and protein by 36.8%. Daily energy expenditure during laying was 2,528 kJ, 5.2 times greater than during incubation. Rate of lipid expenditure during laying was 3.3 times greater than during incubation, and rate of protein expenditure was 8.8 times greater. Of the birds' total prelaying energy, 33.8% was expended during laying, 34.6% during incubation, and 31.6% remained at hatching. An estimated 31.6% of the energy expended during laying was invested in eggs. Sixteenand 18-carbon fatty acids dominated in lipid of the fattest and leanest birds. The major nutrient and energy donors during breeding were 16:0 and 18:1 fatty acids. Svalbard eider eggs weighed ca. 17.5% less and were incubated ca. 1.5 days shorter than eggs from the species' most southerly range limit. This apparent adaptation to arctic existence gave an estimated energy savings of 6.5% during breeding. Received 27 September 1989, accepted 4 April 1990. DURING reproduction, female waterfowl require substantial nutrients, mainly lipids and protein, both for egg synthesis and as an energy source during laying and incubation. The pattern of nutrient acquisition for and allocation to reproduction differs among various waterfowl species. Some, like the Ruddy Duck (Oxyura jamaicensis), depend almost exclusively on dietary intake throughout breeding (Tome 1984). Ring-necked Ducks (Aythya collaris; Hohman 1986) and Mallards (Anas platyrhynchos; Krapu 1981) obtain most of the protein required for egg production from the diet, while endogenous lipid reserves supply much of the fat needed for egg production and the energy for incubation. Most Arctic-nesting geese, however, feed sparsely during laying and incubation, and draw heavily on endogenous reserves stored before arrival on the breeding grounds (Ryder 1970, Ankney 1977, Ankney and MacInnes 1978, Raveling 1979). Female Common Eiders (Somateria mollissima borealis) (hereafter, Eiders) feed heavily near nesting islands during the 4-6 weeks before laying, and increase body weight by approximately 20% above winter levels (Gorman and 3Present address: Sofiesgt. 74,0454 Oslo 4, Norway. Milne 1971). They then fast completely during incubation (Cooch 1965: 30, Gorman and Milne 1971, Milne 1976, Korschgen 1977) and apparently during laying as well (Korschgen 1977); the nutrients and energy required for both producing and incubating a clutch of eggs are drawn entirely from endogenous reserves. The Eider represents an extreme case of seasonal negative energy and nutrient balance in breeding birds. Milne (1976) and Korschgen (1977) investigated changes in the body weight and composition of Eiders throughout the year, and Korschgen (1977) studied weight changes in selected organs and muscles mainly during incubation. Neither study presented detailed data on the changes in weight and body composition that occur in laying when the rate of energy and nutrient expenditure is substantial. Our aim was to investigate the extent and pattern of endogenous nutrient and energy expenditure during laying and incubation in female Eiders breeding in the high Arctic. We also provide comparative data from a population breeding near the species' northern range limit. STUDY AREA AND METHODS The study was conducted at Ny-Alesund in the Kongsfjord region of West Spitsbergen (78?55'N, 660 The Auk 107: 660-668. October 1990 This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 05:47:30 UTC All use subject to http://about.jstor.org/terms October 1990] Arctic Breeding in Female Eiders 661 12000'E) in the Svalbard (Norway) archipelago during 1982. Eiders returned to the Kongsfjord region around mid-April after wintering farther south. Birds concentrated in patches of open water near the mouth of the fjord to forage before nesting. Pairs began flights to the inner fjord in late May, apparently to investigate ice conditions near breeding islands there. Eiders usually concentrate breeding efforts on five major islands in the inner Kongsfjord, as well as near the research station at Ny-Alesund. Laying often begins at different times on adjacent islands because of local variation in ice conditions (Parker and Mehlum in press). Consequently, all birds collected for body composition analysis were collected at the Ny-Alesund colony. Females were collected at four precisely known stages of the reproductive cycle designated as (1) two-three weeks before laying: females collected shortly after pairs began to arrive near the Ny-Alesund colony (i.e. 2-3 weeks before laying began [n = 4]); (2) prelaying: females with large follicles collected just before laying and within 3 days of commencement of laying in the colony (n = 7); (3) postlaying: females collected after 2-3 days of incubation (mean = 2.1), each checked regularly during laying to minimize the possibility of dump nesting or loss of eggs to predators (n = 7); and (4) hatching: females collected on the nest with hatched or hatching young (n = 8). An additional 14 females at this stage were captured and weighed to increase the sample size of bird weights at hatching. Immediately after collection, birds were weighed (total carcass weight) on a Salter spring scale to the nearest 10 g. They were then completely hand-plucked and singed. The intestines (emptied), gizzard (emptied), liver, both pectoral muscles, and the ovary with oviduct were excised, and wet weights were recorded to the nearest 0.1 g. The featherless carcass (including excised muscles and organs) was weighed (featherless carcass weight) and frozen at 20?C in double plastic bags. In preparation for the body composition analysis, the frozen material was sawed on a band saw into pieces and homogenized in a food grinder. The water content of each carcass was determined by drying duplicate 15-g samples to constant weight in a vacuum oven for 2 days at room temperature and ca. 1 day at 30?C. The remaining material was burned at 600?C to constant weight (for approx. 4 h) to obtain ash values. Total lipid was determined with a modified Folch extraction (chloroform-methanol), and total protein by the macro-Kjeldahl method with protein expressed as the product of nitrogen times 6.25. Both lipid and protein determinations were based on 6-10 g samples, usually in triplicate (Holm et al. 1973). Calculation of energy content in lipid is based on a conversion factor of 38.53 kilojoules per gram (kJ g-1), as direct calorimetry of fat samples (n = 9) from both fat and lean birds gave this same value. The energy content of protein was derived using a standard conversion factor of 19.67 kJ.g-l (Pullar and Webster 1977). The energy in subsamples of total homogenate from nine different carcasses, including individuals from each of the four classes of breeding birds, was determined by direct calorimetry. These direct values were compared with total energy values of the same birds derived by calculation as a check for accuracy. Energy values throughout are expressed in kilojoules (4.184 kJ = 1 kcal). Samples of homogenate from the fattest bird collected 2-3 weeks before laying and the leanest bird collected at hatching were analyzed for fatty-acid composition using standard gas chromatography methods. All analyses were done at the Institute for Nutrition Research, School of Medicine, University of Oslo, Oslo, Norway. Statistical comparisons of carcass, organ, muscle, lipid, protein, water, and ash weight were made using one-way analysis of variance with significance level set at P < 0.05.