Predation on Rhinoceros Auklet eggs by a native population of Peromyscus

Predation by Keen's mice (Peromyscus keeni) was the single greatest cause of egg loss for Rhinoceros Auklets (Cerorhinca monocerata) at the seabird colony on Triangle Island, British Columbia in 1998. Despite studies suggesting that gape-limited rodents are unable to open large eggs, mouse depredation was likely responsible for the loss of more eggs than all other causes combined, with mice commonly opening and eating eggs of nearly twice their mass. In one study plot, mice depredated up to 34% of eggs. This high predation rate is likely related to temporary egg neglect by foraging parents. We suggest that egg depredation may increase in years of low marine productivity, when adults increase foraging time.