Breeding Biology of the Rhinoceros Auklet in Washington

Abstract

During 1974 through 1983, we investigated the breeding biology of the Rhinoceros Auklet (Cerorhinca monocerata) at three main colony sites on the coast of Washington: Destruction Island (offshore) and Protection and Smith islands (inland islands of the Strait of Juan de Fuca). Average burrow densities were higher offshore, where the auklets nested on shrub-covered slopes; inland auklets nested on grassy slopes and level areas. Egg-laying patterns varied among years and populations, although initiation dates on all islands were similar. The incubation periods averaged 45 days and ranged from 39 to 52 days. Chicks were brooded, on average, for 3.9 days (range zero to 9 days). On Protection Island, early-hatched young grew more rapidly than chicks hatched at a later date. Chicks on offshore islands were fed a variety of fish, whereas those on inland islands were fed primarily two species. The inland chicks were fed heavier fish loads, reached heavier peak body weights, and were heavier when they fledged than were offshore chicks. Breeding success was higher on the inland colony sites.