We report a specimen that appears to be a hybrid between Swainson's Hawk (Buteo swainsoni) and Rough-legged Hawk (B. lagopus), which, to our knowledge, is the first hybrid specimen for the genus. There are few reports of hybridization between Buteo species, most of which have been observations of interspecific nesting pairs. The specimen described herein was collected in Louisiana and initially identified as a Rough-legged Hawk because of its feathered tarsi and the dark bellyband and carpals. A DNA sequence from the maternally inherited mitochondrial ND6 gene was identical to a published sequence for Swainson's Hawk. Nuclear DNA sequences from two introns contained only five variable sites among a panel of five potential parental taxa, but the hybrid sequence was most consistent with parentage by Rough-legged and Swainson's hawks. The feathered tarsi of the hybrid strongly suggested that the father was either a Rough-legged or Ferruginous hawk (B. regalis), the only North American raptors other than Golden Eagle (Aquila chrysaetos) that have feathered tarsi. Plumage and size characters were inconsistent with those of Ferruginous Hawk, and, other than the darkly pigmented leg feathers, were intermediate between the light morphs of Swainson's and Rough-legged hawks. The breeding range of Swainson's Hawk in Alaska and northern Canada is poorly known, but it overlaps that of the Rough-legged Hawk in at least a few locations, albeit at low densities, which may be a factor in hybridization. The occurrence of this hybrid is evidence of the potential for interbreeding between North American members of the genus Buteo, most of which are genetically closely related. Such hybridization could have implications for genetic diversity, adaptation, or the evolution of reproductive barriers. In any case, such hybrids present field and museum identification problems.
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Vol. 118 • No. 1