I analyzed regurgitated pellets, prey remains, and video recordings to describe Ferruginous Hawk (Buteo regalis) diet in two grasslands in New Mexico, USA, the Estancia Valley and the Plains of San Agustin, that differed in anthropogenic alteration. Video monitoring revealed Ferruginous Hawks provisioned nestlings with more biomass than pellet analysis estimates from the same nests. Three mammalian prey species, Botta’s pocket gopher (Thomomys bottae), Gunnison’s prairie dog (Cynomys gunnisoni), and desert cottontail (Sylvilagus audubonii), contributed similar proportions to Ferruginous Hawk diet in percent biomass while Botta’s pocket gopher dominated diet in percent frequency. Ferruginous Hawks breeding in the anthropogenically-altered Estancia Valley consumed more Gunnison’s prairie dogs than Ferruginous Hawks in the rural Plains of San Agustin, regardless of calculative method, while Ferruginous Hawks in the Plains of San Agustin consumed more desert cottontails. From 1998-2005, Ferruginous Hawks in the Estancia Valley produced significantly more fledglings per nesting attempt than Ferruginous Hawks in the Plains of San Agustin. This indicated that the persistence of colonial mammals like Gunnison’s prairie dogs, which offer minimal predatory search time, may have increased Ferruginous Hawk reproductive output and helped to offset the effects of moderate levels of human development. Intact Gunnison’s prairie dog colonies should be conserved in the Estancia Valley to enable maintenance of current Ferruginous Hawk productivity levels in the midst of increased human development, a threat that is becoming more pronounced. Further documentation of behavior and food requirements of Ferruginous Hawks in anthropogenically-altered landscapes is necessary to conserve this grassland obligate whose habitat is rapidly diminishing.
Keeley, W.H. and M.J. Bechard. 2011. Flushing distances of Ferruginous Hawks nesting in rural and exurban New Mexico. The Journal of Wildlife Management 75(5):1034-1039.