Breeding Ecology of Kittlitz’s Murrelets at Agattu Island, Aleutian Islands, Alaska

—The Kittlitz’s Murrelet (Brachyramphus brevirostris) is a poorly-known species of alcid and a seabird of conservation concern. Nesting murrelets were discovered at Agattu Island in the western Aleutian Islands, and a field study provided new information on nest site selection, chick growth rates and reproductive success. Twelve ground nests were located in upland habitats (441 masl) at inland areas of Agattu (2.3 km from shore). All nests contained one egg or chick. Murrelets tended to nest in association with a ground cover of orange crustose lichens, bare ground, small rocks and graminoids. Estimates of growth rates for the body mass of nestling Kittlitz’s Murrelets were lower (KL < 0.10) than published estimates for other small-bodied alcids with semiprecocial young (KL = 0.14 to 0.23). Murrelet young departed from nests after 30 days of growth at 47% of adult mass but at 80% of adult wing length. Optimal wing-loading may ensure successful dispersal flights from terrestrial nest sites to ocean habitats. Survival of eggs and young were low during the incubation (0.26; 30 d) and brood-rearing periods (0.22; 30 d), leading to a low probability of nest survival (0.06). Losses during incubation were mainly due to avian predators, whereas mortality of young after hatching was caused by inclement weather. Kittlitz’s Murrelets have a suite of life-history traits associated with low reproductive potential (small clutch size, slow growth and poor reproductive success) and may have limited ability to recover from population declines. Received 27 February 2008, accepted 1 June 2009.