Predation on Rhinoceros Auklet eggs by a native population of Peromyscus

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