Breeding ecology of radio-marked Marbled Murrelets, Brachyramphus marmoratus, in Desolation Sound, British Columbia
Bradley, Russell W.
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Understanding the population biology of a species requires thorough study of its breeding behaviour and success. The Marbled Murrelet is a small alcid seabird which cryptically nests at inland sites in old-growth trees. Concern for murrelet populations, primarily from breeding habitat loss, has led to listing of the species as threatened or endangered over most of its range. However, because of its elusive breeding, reproductive ecology of Marbled Murrelets is still poorly understood. I investigated the breeding ecology of radio marked Marbled Murrelets in Desolation Sound, British Columbia. Movement patterns of radioed birds showed that breeding state and success can be accurately inferred with radio telemetry. Male breeding birds visited their nests, and likely provisioned young, more than females during chick rearing. The male bias was primarily due to a reduction in female visitation during late chick rearing. These findings offer a behavioral explanation for the annual male bias of birds flying inland during the chick rearing period at Theodosia Inlet in Desolation Sound from 1994-1999. Early breeding birds commuted further from foraging areas to nests, and nested at sites of steeper slopes than later breeding birds. Earlier breeding birds were more successful, while higher nest site elevation, steeper nest site slope, and longer commuting distance were all associated with greater success. Data from radio marked birds showed no evidence to suggest that nesting near forest edges, particularly natural edges, reduces reproductive success in Marbled Murrelets. Advantages of steeper nest site slopes and close proximity to edges, like nest site access, may outweigh the potential costs of nest predation in our study location, which is free of human habitation in murrelet breeding areas.