Adaptive perch selection as a mechanism of adoption by a replacement Bald Eagle

Abstract

Replacement of lost mates within the same nesting season has been recorded in 26 raptor species (Newton 1979). Only three species (Cooper’s Hawk, Accipiter cooperii; Northern Goshawk, A. gentilis; and Peregrine Falcon, Falco peregrinus) have exhibited full adoption, i.e., incubation of eggs and/or rearing of young by an unrelated, replacement mate (Rohwer 1986). Neither mate replacement within the same season nor adoption has been recorded for Bald Eagles (Haliaeetus leucocephalus). Herrick (1932) describes two Bald Eagle mate replacements of 11 and 14 weeks’ duration, but both occurred over winter (October-February), prior to nesting. Adoption may be adaptive for long-lived species, through establishment of a pairbond for future seasons, if: (a) following mate loss and nest failure, renesting within the same season is unlikely; (b) the probability of starting the next breeding season with an established pairbond is increased with adoption; and (c) experienced pairs tend to have higher breeding success than new pairs (Rohwer 1986).

Citation

Grubb, Teryl G.; Forbis, Larry A.; McWhorter, Marta; Sherman, David R. 1988. Adaptive perch selection as a mechanism of adoption by a replacement Bald Eagle. Wilson Bulletin 100 (2) 302-305