Body-mass Dynamics of King Eiders During Incubation

Abstract

Several studies have demonstrated the importance of maintaining parental body reserves to successfully complete incubation or to raise offspring without affecting parental survival (e.g. Tombre and Erikstad 1996, Merila and Wiggins 1997, Zicus 1997). Restraint in use of reserves could be favored if females with greater reserves after laying had higher reproductive success or survival. Erikstad and Tveraa (1995) suggested that optimal clutch size in Common Eiders (Somateria mollissima) is determined by an interaction between allocation of endogenous reserves to egg production and energy needed for incubation and brood rearing. Depletion of reserves before hatching may lead to nest failure through nest abandonment or decreased nest attentiveness. Moreover, high nest attentiveness may reduce predation by reducing the amount of time that nests are unattended and by reducing incubation duration (Milne 1976, Aldrich and Raveling 1983). Nest failure during incubation, therefore, may be a consequence of nest abandonment or predation, either of which may be linked to female body condition. Gloutney and Clark (1991) found that female Mallards (Anas platyrhynchos) and Northern Shovelers (A. clypeata) that nested successfully were heavier than unsuccessful females, but this pattern was absent in Blue-winged Teal (A. discors). Canvasbacks (Aythya valisineria) and Redheads (Aythya americana) used stored reserves during egg production and incubation, but body mass during late incubation predicted nesting success only for yearling Canvasbacks (Arnold et al. 1995). Blums et al. (1997) investigated this hypothesis in a large sample of Common Pochards (Aythyaferina) and Tufted Ducks (A. fuligula); late-incubation body mass predicted nesting success in Tufted Ducks and adult Common Pochards, but not in yearling Common Pochards. Hence, whereas all three studies documented effects of body mass on nesting success, in at least some species and/or age groups, these effects did not apply. Because arctic-nesting species contend with colder temperatures and possibly lower food availability