Causes and Consequences of Variation in Nest Success of King Eiders (SOMATERIA SPECTABILIS) at Karrak Lake, Northwest Territories
Date
1999-03
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Masters
Abstract
Factors influencing nest success and breeding-site fidelity were investigated in king eiders (Somaterict spectabilis) at Karrak Lake, NT. during 1995-1998. Island-nesting king eiders had higher nest success (range: 30-89%) than that reported from mainland-nesting populations (e.g.. Lamothe, 1973: Bromley and Brook, 1997), and nested at higher densities on islands (range: 46-139 nests/km2) than in mainland habitat (~0 nests/km2). On islands, predation appeared to be the main cause of
nest failure. King eiders experienced greater nest success on islands farther from the mainland, suggesting that mammalian predation influenced king eider nest success, as mammalian predators were rarely seen on islands. Consequently, king eiders nested on islands farther from the mainland. Additionally, king eiders derived protective associations by nesting near aggressive species. Comparison of daily nest survival rates revealed that in some years, king eiders may improve nest success by nesting on islands with glaucous (Larus hyperhoreus), herring (L. argentatus), and Thayer's (L. thayeri) gulls and arctic terns (Sterna paradisaea). Similarly, nest fate was improved, and fewer eggs were lost from nests that overlapped for longer time periods with lesser snow (Chen caerulescens), Ross's (C. rossii). and Canada (Branta canadensis) goose nests in 1997.
King eider females lost 32% of pre-incubation body mass during incubation, showing strong reliance on endogenous reserves during incubation. Body condition (corrected for incubation stage at capture and body size) of unsuccessful females was marginally lower than successful females, suggesting that females with fewer reserves abandoned nests more readily than females with greater reserve levels. Alternatively, females in poorer condition may have reduced nest attentiveness to increase feeding opportunities and, consequently, exposed their nests to predators. Female body condition declined with initiation date, and condition may be a determinant of nest success in years with late springs when endogenous reserves may be depleted below critical levels before completion of incubation.
Females were more likely to return to the same island to nest in subsequent years following a successful nesting attempt. However, dispersal did not improve nest success, nor did it delay nesting, reduce clutch size, or deplete endogenous reserves, suggesting no cost or benefit to short-distance dispersal. Females moved to nearby islands after nest failure, and only two females nested on islands of neighbouring lakes, suggesting high fidelity to nesting areas. Females may be reluctant to make long-distance movements between nesting areas, as Karrak Lake may be a highly productive nesting and brood-rearing area. Although there were no costs associated with short-distance dispersal. long-distance dispersal may significantly delay nesting, thereby reducing endogenous reserves, and may be particularly deleterious in species such as king eiders which rely on reserves for successful incubation.
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Degree
Master of Science (M.Sc.)
Department
Biology
Program
Biology