Relationships between breeding status, social -congregation attendance, and foraging distance of Xantus's Murrelets

At night during the breeding season, Xantus's Murrelets (Synthliboramphus hypoleucus) congregate on the water adjacent to nesting colonies. We examined relationships of attendance at these nocturnal congregations, breeding status, and daytime foraging locations of radio-marked Xantus's Murrelets from Anacapa Island (33 in 2002, 44 in 2003) and Santa Barbara Island (35 in 2002) in the California Channel Islands. Murrelets that spent more nights attending congregations were located closer to the island during the day, so regular attendance at the congregations may have constrained daytime traveling distances to foraging locations. In mid-May 2003 home-range sizes increased while congregation attendance decreased, likely indicating the end of colony attendance and declining availability of prey near Anacapa Island. In both years, incubating murrelets foraged farther from the colony than did nonbreeding murrelets, suggesting that breeding and nonbreeding murrelets use different foraging strategies to meet their energetic requirements.