Breeding and Natal Dispersal, Nest Habitat Loss and Implications for Marbled Murrelet Populations

1 Wildlife Biologist, Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99705 2 Wildlife Biologist, U.S. Fish and Wildlife Service, U.S. Department of Interior, 2800 Cottage Way, Room E1803, Sacramento, CA 95825 Abstract: Evidence of breeding and natal dispersal in alcids is typically provided by the resightings of banded birds, the establishment of new colonies, and/or evidence of immigration to established colonies. The difficulties in banding, observing, and censusing Marbled Murrelets at nesting areas preclude using any of these methods for this species. Based on the limited number of nests observed in consecutive breeding seasons, breeding site fidelity (birds breeding in the same nest as the previous year) may be lower than most other alcids. This is likely due to low breeding success associated with high levels of nest predation. By contrast, annual use of nest stands suggests fidelity to a nesting area may be high. Natal dispersal, the breeding at locations away from their fledging site, is likely similar to that of other alcids. Loss or degradation of previously occupied nesting habitat will result in the displaced breeders prospecting for new nest sites. In areas with no unoccupied available habitat, this could result in birds being prevented from breeding, attempting breeding in suboptimal habitat, or increasing the distance dispersed from the previous breeding sites. Each of these is likely to result in a decrease in reproductive output. Dispersal patterns need to be considered when assessing the importance of stands and the status of populations. The small population size and fragmented nature of the remaining breeding habitat could increase the time required for prospecting birds to locate recently matured old-growth forest, resulting in underestimating the importance of a stand. Additionally, birds could be dispersing from regions of high production of young to areas with low production but where recruitment opportunities are higher, partially hiding the low reproduction of the latter population.