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

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
VARIATION IN ARRIVAL BODY CONDITION AND REPRODUCTIVE STATUS
OF WHITE-WING SCOTER HENS AT CARDINAL LAKE, NT
Stuart Slattery¹, Kristina Norstrom 2 , Karen Petkau¹, and Daniel Esler 3
¹ Ducks Unlimited Canada, Box 1160, Stonewall, Manitoba, ROC 2Z0; s_slattery@ducks.ca;
k_petkau@ducks.ca
² Formerly Ducks Unlimited Canada; Box 1160, Stonewall, Manitoba, ROC 2Z0
3 Centre for Wildlife Ecology, Simon Fraser University, 5421 Robertson Road, Delta, British
Columbia, V4K 3N2
Continental scoter populations (all three species combined) declined by about 58% over the past 30
years, with local reductions approaching 70% in their core breeding area, the Northwest Territories.
The reasons for these declines are unknown. However, scoter breeding, migrating, and wintering
habitats are undergoing direct or indirect anthropogenic change, which could have implications for
their ability to acquire nutrients for successful breeding and could contribute to population decline.
Our challenge in assessing this hypothesis is that we do not know whether these populations are
sufficiently nutritionally constrained and, if so, where northern scoters acquire nutrients for breeding,
hence where to begin looking for factors potentially causing constraint. These knowledge gaps can
in part be filled by developing an understanding of basic nutritional ecology for scoters breeding in
northern latitudes. The goal of this presentation is to assess annual and seasonal variation spring body
mass and condition, and determine the relationship between nutritional status and egg production for
white-winged scoters (Melanitta fusca) captured at Cardinal Lake, about 80 km south of Inuvik, NT.
From 2002 - 2004, we caught 77 females and 179 males during the prenesting and early egg laying
periods. Both sexes were weighed and measured, and then hens were palpated for external indicators
of reproduction and marked with nasal discs and radio transmitters for other research. In 2004, we
also collected blood samples from females to determine reproductive status based on concentrations
of vitellogenin, a yolk precursor. Although peak nest initiation dates varied little annually, female
body condition (mass corrected for structural size) varied greatly due to a 200 g variation in body mass
and no annual variation in structural size. Body condition, structural size, and mass of males did not
vary annually. Within years, body condition did not covary with capture date for either sex and egg
production was largely confined to hens over 1400g. Together, these results suggest that egg laying in
scoters may be highly sensitive to environmental conditions on migration and breeding areas.
NOV. 7-11, 2005 ANNAPOLIS, MARYLAND, USA
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