The influence of breeding status and nest site location on marine habitat use by marbled murrelets brachyramphus marmoratus

The Marbled Murrelet Brachyramphus marmoratus is a threatened seabird that relies on old-growth forest for nesting. We compare marine space use between breeding and non-breeding birds, and how marine home range locations and overlap vary with respect to nesting location and breeding status. We collected very high frequency (VHF) radio-telemetry data in southern British Columbia from Clayoquot Sound (190 birds; 2000-2002) and Desolation Sound (206 birds; 1998-2001). The sites differ strongly in their oceanic exposure and surrounding terrestrial features. Kernel utilization distribution-based estimates showed that breeders and non-breeders had similar overall distributions, but breeders were more spatially aggregated. Pooled home ranges of non-breeders were larger than those of breeders, but the distributions of individual home range sizes did not differ significantly by breeding status. However, compared with non-breeders, breeding murrelets were more likely to share their home range with other breeders. Home range sizes were larger and commuting distances were longer at Desolation Sound than at Clayoquot Sound; the average home range size for individuals was 241 +/- 6.7 km(2) at Clayoquot Sound and 330 +/- 8.8 km(2) at Desolation Sound. Individuals that nested closer together were more likely to share their marine home range in Desolation Sound, but not at Clayoquot Sound. Commuting distance to a nest site was not related to home range size at either site. Our results support the hypothesis that, at a local scale, breeding murrelets congregate at specific foraging areas and are not strongly constrained by commuting distance to nesting locations. Our results also support the concept that home range size may be indicative of the overall habitat quality of an area. We quantify connectivity between terrestrial and marine habitats and highlight important historical foraging locations.