Red-tailed Hawk dietary overlap with Northern Goshawks on the Kaibab Plateau, Arizona

We determined food habits of Red-tailed Hawks (Buteo jamaicensis) for comparison with published information for Northern Goshawks (Accipiter gentilis) to evaluate potential competition on the Kaibab Plateau, Arizona. We collected prey remains and pellets from 42 Red-tailed Hawk nests at the end of the nesting season between August-October 1998-2001, and opportunistically from below nest trees during site visits, May-July 2000-01. We identified 478 prey items, including 17 mammal, 7 bird, and 2 reptile species. Prey species frequency did not vary among years (P = 0.3), across habitat types (P = 0.8), or by collection technique (P = 0.4). Annual food niche breadth for Red-tailed Hawks averaged 0.57. Published mean niche breadth for Northern Goshawks was 0.32 supporting that Red-tailed Hawks were feeding generalists, while Northern Goshawks were more specialized. However, 48% of Red-tailed Hawk diet on the Kaibab Plateau consisted of species comprising a major portion of the documented diet of Northern Goshawks, including Nuttall's cottontail (Sylvilagus nuttallii), golden-mantled ground squirrel (Spermophilus lateralis lateralis), rock squirrel (S. variegates grammurus), and Northern Flicker (Colaptes auratus). Because raptor communities with high dietary overlap and lack of prey partitioning show food-limited nesting success, greater agnonistic behavior, and territoriality, Red-tailed Hawks could be negatively affecting Northern Goshawks on the Kaibab Plateau.