EMBRYO METABOLISM AND EGG NEGLECT IN CASSIN AUKLETS

Incubation attendance by Cassin's Auklets (Ptychoramphus aleuticus) was determined by daily nest monitoring. The incidence of natural egg neglect was highest during the first third of the incubation period (incubation length of 38 days when parents were continuously present) and lowest between 12 and 25 days after laying. The latter corresponds to the period of most rapid embryonic growth rate. The pattern of auklet embryo metabolism is similar to that of other precocial species with prolonged incubation periods, with two differences: unpipped auklet embryos show their most rapid rise in metabolic rate relatively earlier in the incubation period. Auklet embryos have an unusually long plateau (10 days) in metabolic rate before begining pipping. A rapid increase in metabolism is coincident with the five-to seven-day hatching process. Embryos surviving chilling had lower metabolic rates (after rewarming) than continuously incubated eggs of the same chronological age. The reduction of metabolic rate and resulting retarded development may account for the prolonged duration of incubation observed for both naturally and experimentally neglected auklet eggs.