Mass and date at departure affect the survival of Ancient Murrelet Synthliboramphus antiquus chicks after leaving the colony

I compared the timing of colony departure and body mass of 53 Ancient Murrelet Synthliboramphus antiquus chicks that were retrapped as adults in Haida Gwaii, British Columbia, with those of 3992 chicks not retrapped. If the probability of recapture is a measure of survival, survival was related to both mass and date. Chicks that left the colony at 26 g or less had a lower chance of survival than heavier chicks, and those that left after the median date of departure survived better in some years than those that left earlier. The effect of date was not related to a seasonal change in departure mass because chick mass declined with departure date. I suggest that, because of heavy adult mortality during breeding, the timing of breeding in the Ancient Murrelet is based on a compromise between the optimum dates for chick and adult survival. This is in contrast to evidence from other, nonprecocial, seabirds.