GENETIC-EVIDENCE FOR LOW-FREQUENCY OF EXTRA-PAIR FERTILIZATIONS IN NORTHERN GOSHAWKS

We collected blood for allozyme analysis from Northern Goshawks (Accip iter gentilis atricapillus) on the Kaibab Plateau in northern Arizona during 1991-1993 to quantify frequency of extra-pair fertilizations (E PFs). Northern Goshawks are socially monogamous, territorial, noncolon ial, synchronous breeders, and their nests are relatively far apart, c haracteristics that suggest that EPFs should be low. We sampled 103 ad ults and 122 nestlings from 64 nests. Both putative parents were sampl ed at 39 nests, but we were able to capture and sample only one putati ve parent at 25 other nests (84%, female only: 16%, male only). Of the 39 complete families sampled, only 1 of 77 (1.3%) nestlings (or in 1 of 39 clutches, 2.6%) had a genotype not consistent with both parents; the male was excluded as the genetic father of this nestling. When th is estimate was adjusted based upon the probability of excluding a put ative father when he is not the actual father, the estimate of nestlin gs sired by EPFs was 9.4% in 1991 and zero in 1992 and 1993. There was no evidence of egg-dumping. Our data suggest that EPFs are infrequent in Northern Goshawks breeding in northern Arizona, a result consisten t with characteristics of their mating system.