I here describe an occurrence of an apparent intrusion by a second-year (SY) female Cooper’s Hawk (Accipiter cooperii) into an occupied territory after incubation by a resident adult (after-second-year; ASY) female had commenced. The adult female was displaced from the nest on multiple occasions, resulting in an abandonment of the nest by the resident adults. The intruding female did not use the abandoned nest but briefly exhibited behaviors consistent with initiating a new nesting attempt. However this effort was also abandoned and no young were produced at the territory.

Among Cooper’s Hawks, both females and males exhibit delayed plumage maturation in which SY birds are visually distinct from adults (Rosenfield 2018). Breeding by SY females still in juvenile plumage is common. A tracking study of juvenile females showed that nearly all females who survived into their second year then nested as SY birds (Millsap et...

You do not currently have access to this content.