Second North American Sea Duck Conference - Patuxent Wildlife ...

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SECOND NORTH AMERICAN SEA DUCK CONFERENCE FACTORS DETERMINING HERRING GULL FORAGING SUCCESS WITHIN AN ARCTIC COMMON EIDER DUCK COLONY Karel Allard¹, H. Grant Gilchirst², and Antony Diamond¹ ¹Atlantic Cooperative Wildlife Ecology Research Network, P.O. Box 45111, University of New Brunswick, Fredericton, NB E3B 6E1 CANADA; h77ct@unb.ca ²Canadian Wildlife Service, National Wildlife Research Centre, 1125 Colonel By Drive, Raven Road, Carleton University, Ottawa, ON K1A 0H3 CANADA Reproductive success of many colonial nesting birds is partly determined by loss of eggs and young to avian predators that nest within colonies. We investigated the ecology of herring gulls (Larus argentatus) foraging within a common eider (Somateria mollissima) colony in the Canadian Arctic. We hypothesized that predation rates of eider eggs and ducklings by gulls vary in relation to environmental conditions, prey alternatives, and risk of injury. 1) We studied gull predation of eider eggs and quantified how herring gull numbers, search rate, and attack success varied with environmental (weather, tide, available light, etc.) and behavioral (eider reproductive phenology, nest density, etc.) factors. Herring gulls did not force incubating hens off their nests, and took eggs only from unattended clutches. Consequently, gulls foraged more intensively and were most successful during eider egg-laying when hen nest attendance was intermittent. 2) We studied gull predation of ducklings during passage of eider broods from nest to sea. We assessed the effect of environmental variables on search and duckling capture rates by gulls, paying particular attention to annual variation. Capture rates were low and variable across years, but lowest when lemming abundance was high, despite consistent encounter rates between gulls and eider broods. Frequency of eider defensive response to foraging gulls was higher in low lemming years, and highest in the year following the lemming abundance peak. Otherwise, gulls searched most intensively and were most successful during windy conditions, when they could hover over broods. 3) We manipulated food availability within foraging territories actively defended by pairs of resident gulls. Territories varied in both size and in numbers of eider nests they contained. Both territory attendance and defense was largely determined by prey abundance within territories. Territorial residents were responsible for more than half of all egg depredations within the colony, and ultimately protected nesting eiders from other gulls by actively excluding them from their feeding territories. Our findings stress the importance of assessing costs, returns and risks for predators before making broad generalizations about their influence on colonial nesting prey. Our results also suggest that risk of injury may influence the foraging behavior of herring gulls as they attempt to maximize the trade-off between energy gain and foraging costs. 62 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005
SECOND NORTH AMERICAN SEA DUCK CONFERENCE INCUBATION BEHAVIOR OF KING EIDERS ON ALASKA’S COASTAL PLAIN Rebecca McGuire, Abby Powell, and Robert Suydam USGS Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska, Fairbanks; ftrlm@uaf.edu The patterns and constancy of incubation are unknown in king eiders (Somateria spectabilis). Incubating females face conflicting selection pressures; maintaining a favorable thermal environment for embryo development, maintaining a favorable energy balance for themselves, and minimizing the risk of predation on themselves and their eggs. As a response to these discrepant demands, large waterfowl species have apparently developed the capacity to accumulate such significant fat reserves before nesting that they can rely predominantly on endogenous reserves to sustain themselves during incubation. King eiders are near the extremes of the waterfowl continuum in severity of climate and reliance on nutrient reserves and thus an interesting species in which to study the incubation behavior. We located and monitored king eider nests at two sites on Alaska’s North Slope, Teshekpuk and Kuparuk, from 2002-2005. We placed artificial eggs containing HOBO data loggers in a sample of these nests (n = 10/site/year). We set the data loggers to record nest temperature every 2 minutes. Additionally, we weighed females upon arrival to the breeding grounds and again near hatch. In 2005, females were also weighed during mid-incubation. Incubation constancy was significantly higher at Kuparuk (99%) than it was at Teshekpuk (95%). Most recesses occurred between 2:26PM and 3: 37PM. Females nesting on islands in lakes took fewer, slightly longer breaks than mainland nesters. There is some indication that females may arrive on the breeding grounds in slightly better condition at the Kuparuk study site. Nest success was not significantly different between sites but tended to be higher at Kuparuk. We relate the incubation constancy of individuals to environmental and nest habitat characteristics. We examine the variation in incubation constancy, nest success, and spring condition of females between the two sites. NOV. 7-11, 2005 ANNAPOLIS, MARYLAND, USA 63
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