Factors influencing subcolony colonization and persistence in a colonial seabird, the common murre Uria aalge

Abstract

Within an established seabird colony the choice of where to settle can be influenced by site fidelity, natal philopatry or public information. To form a new colony individuals must choose before philopatry has been established or public information is available. We explored the intra- colony dynamics of common murres Uria aalge, specifically the formation and persistence of new subcolonies within a larger colony complex composed of numerous contiguous groups. We investi- gated the effects of (1) environmental conditions that influence the prey base, (2) predator distur- bance, and (3) population size change on colonization patterns and modeled the persistence of recently colonized murre subcolonies as a function of their starting population sizes. Marine environ- mental conditions in the 2 winters previous to the breeding season had more influence than demo- graphic and predator factors on whether subcolony colonizations occurred. The number of murres in the first year of colonization helped to explain the persistence of the subcolony, regardless of the amount of available nesting habitat within a subcolony area. Subcolonies that started out larger were more likely to persist. The results support the theory that the proportion of the entire murre popula- tion that attempts to breed in a given year is higher in years with favorable environmental conditions prior to the breeding season. Increased knowledge of murre colony formation may help scientists and managers understand the potential for recolonizations after colony extirpations or better predict the success of management actions such as social attraction or habitat modification.