The
Influence of Avian Predators on Egg and Duckling Survival of Common
Eider Ducks (Somateria mollissima) on Southampton Island, Nunavut
Karel Allard
PhD. student
Committee:
DR. ANTONY DIAMOND
University of New Brunswick
DR.
H. GRANT GILCHRIST
Canadian Wildlife Service
ABSTRACT
Although waterfowl species are generally well studied, knowledge of sea duck ecology is limited. This is despite the fact that recent surveys indicate that dramatic population declines have occurred among several sea duck populations in North America and Greenland (e.g. king eiders (Somateria spectabilis) in the Western Arctic and common eiders (Somateria mollissima) in the Eastern Canadian Arctic). The reasons for these declines are unknown. In addition, the conservation and management initiatives that are required to reverse these downward trends have not been identified due to lack of information. Consequently, the Canadian Wildlife Service, the U.S. Fish and Wildlife Service, and the Circumpolar Seabird Working Group have identified the study of eider ecology as a national and international priority.
In general, reproductive failure is much less likely to affect population numbers than is adult mortality, particularly among long-lived sea duck species. However, consistent reproductive failure can potentially slow the recovery of populations reduced in size by other factors (e.g. over-harvest, oil spills). Predatory birds can have important influences on the reproductive success of colonial birds, and their impacts may vary with large scale changes in the marine environment that influence alternative food sources. For example, in several oceans, gull populations may have been artificially sustained at high levels by discharge of offal from fishing industries. The recent collapse of these fisheries may have forced gull populations to return to feed on natural food sources such as nesting marine birds, including eider ducks. Great black-backed gulls (Larus marinus) were recently identified as the most significant cause of low eider duckling production on the Wolves archipelago in the Bay of Fundy, the largest common eider colony in the Maritime Provinces. Significant losses of eggs and ducklings due to predation by great black-backed and herring gulls (Larus argentatus) have also been recorded for colonies in the Saint Lawrence estuary and in south-west Sweden.
The
long-term impacts of these predation levels on eiders are unknown, as
are the factors that determine predation rates within colonies over
the course of a breeding season. Research of these issues is complicated
by the response of eiders to disturbance. Common eiders nest in colonies,
and they are extremely sensitive to disturbance. Indeed, they often
leave the nest when disturbed and this facilitates high rates of avian
predation. Consequently, visits to colonies by researchers may influence
predator-prey dynamics, which makes interpretation of predation data
difficult. Most previous studies of predation in eider colonies have
suffered from this limitation. Consequently, the factors influencing
predation rates within eider colonies are poorly understood. For example,
it is unclear how predation rates vary annually, in relation to time
of day, time within the breeding season, weather, location within the
colony, common eider nest density, or common eider nest defence behaviour.
This
study will examine the mechanisms and effects of herring gull and parasitic
jaeger (Stercorarius parasiticus) predation on common eiders
using egg placement experiments, detailed behavioural observations from
concealment, and bird banding. The colony is located on a small, treeless
island in the Eastern Canadian Arctic. At this colony, the Canadian
Wildlife Service has built observation blinds and access tunnels that
allow detailed observations of incubating eiders and their predators
without causing disturbance. Four blinds are situated in different parts
of the colony, and this allows the study of how variation in nesting
densities, proximity to the ocean, and proximity to gull nests influence
predation. Observation of banded gulls and eiders also permits the study
of individual behaviour.
PUBLICATIONS
Allard, K., McKay,K. and McKinnon,L. 2001. Sighting of Ruddy Shelducks at East Bay, Southampton Island, Nunavut. Birders Journal 10: 86-89.
Stenhouse, I.J., Truman, K. and Allard, K. 2001. Sightings of Steller's Eider at East Bay, Southampton Island, Nunavut. Birders Journal 10: 160-163.
FUNDING ACKNOWLEDGEMENTS
Canadian Wildlife Service, Prairie and Northern Region
Northern Student Training Program
NSERC (Undergraduate Research Assistantship program)
