Spatial effects in relation to reproductive performance of Common Murres (Uria aalge) at a re-established colony

A main goal of seabird colony restoration is for the colony to become self-sustaining. To do so, elevated rates must be attained in (1) reproductive success and (2) recruitment by immigrants and birds produced at the colony. Thus, an understanding of the factors affecting reproductive success and recruitment at restoration sites is vital. We examined how spatial features at the colony level affected reproductive success of Common Murres Uria aalge (hereafter, murres) over a six-year period at Devil's Slide Rock, California, a colony re-established using social attraction techniques. Clusters of sites with similar egg-laying dates, as well as high hatching and breeding success, occurred in the densest portion of the colony, which was also the last area occupied by murres at the time of extirpation and the first area to be re-colonized. Clusters of sites with low success occurred in outlying, low-density portions of the colony. Breeding success, influenced largely by high fledging success, averaged > 60% most years. Reproductive success was greatest at breeding sites with earlier egg-laying dates, those in closest proximity to the breeding sites of other murres and the Brandt's Cormorant Urile penicillatus, and those outside Brown Pelican Pelecanus occidentalis disturbance zones. Based on our findings, for future murre restoration projects in the California Current System, we suggest (1) placing social attraction equipment in the area(s) last utilized by murres prior to extirpation, (2) attempting to establish two dense breeding groups, (3) targeting sites already utilized regularly by nesting Brandt's Cormorants, and (4) avoiding sites or habitats prone to disturbance by larger and aggressive species such as Brown Pelicans, Bald Eagles Haliaeetus leucocephalus, or Common Ravens Corvus corax.