Egg neglect under risk of predation in Cassin’s Auklet (Ptychoramphus aleuticus)

Abstract

We tested predictions concerning the significance of egg neglect for the burrow-nesting seabird Cassin’s auklet (Ptychoramphus aleuticus (Pallas, 1811)) at a colony where endemic Keen’s mice (Peromyscus keeni Merriam, 1897) depredate unattended eggs. A video-camera probe was used to monitor neglect and predation in 32 burrows, and mass loss of incubating adults was measured in 12 separate burrows. Incubating birds lost 8.1% of their body mass over obligate 24 h incubation shifts, suggesting that incubation is costly. In response, most pairs (79%) neglected their egg at least once. As predicted, rates of neglect decreased as incubation progressed, and the costs of neglect increased. Rates of neglect increased during periods of strong winds, which create poor foraging conditions at sea. Contrary to predictions, rates of neglect did not increase when burrows were colder and self-maintenance costs were higher. Neglect was risky in that rates of egg loss by predation increased with frequency of neglect. Increased neglect early in incubation and during periods of poor foraging conditions, despite high rates of predation on neglected eggs, is consistent with the existence of a fitness trade-off between costs and benefits of neglect.