No abstract

Despite the unique threats to wildlife in urban areas, many raptors have established successfully reproducing urban populations. To identify variations in raptor breeding ecology within an urban area, we compared metrics of Red-tailed Hawk reproductive attempts to landscape characteristics in Reno and Sparks, NV, USA during the 2015 and 2016 breeding seasons. We used the Apparent Nesting Success and logistic exposure methods to measure nesting success of the Red-tailed Hawks. We used generalized linear models to relate nesting success and fledge rate to habitat type, productivity to hatch date (Julian day) and hatch date to urban density. Nesting success was 86% and 83% for the respective years. Nesting success increased in grassland-agricultural and shrub habitats and decreased in riparian habitat within the urban landscape. Productivity was 2.23 and 2.03 per nest for the breeding seasons. Fledge rates were 72% and 77%, respectively, and decreased in riparian areas. Nestlings hatched earlier with increased urban density and earliest in suburban areas, following a negative quadratic curve. Nesting success and productivity for this population were high relative to others in North America. Productivity increased in habitats where ground prey was more accessible. We suggest that suburban areas, if not frequently disturbed, provide sufficient resources to sustain Red-tailed Hawks over extended periods. As urban expansion continues in arid environments globally, we stress that researchers monitor reproductive output across the urban predator guild to elucidate patterns in population dynamics and adaptation.

No abstract

We examined Red-tailed Hawk (Buteo jamaicensis) nestling diets in Reno and Sparks, NV, USA during the 2015 and 2016 breeding seasons. Field researchers and nest cameras recorded 1348 prey items spanning 28 species at 88 nests. Prey consisted of 86% mammalia, 10% aves and 4% reptilia. Differential prey selection occurred among the population and at individual nests relative to an expected diet. Diet breadth differed between nests and increased with urban density. Avian prey consumption increased relative to mammalian and reptilian prey in impervious areas. When prey items were plotted on a continuous urban density spectrum, mammalian prey increased in the suburban areas and decreased toward the urban core and was inversely correlated with avian prey. Mammalian prey consumption increased and decreased at the end of April and in mid-May before increasing through the remainder of the breeding season (mid-June). Avian prey consumption peaked in May and increased through the season, and reptilian prey varied little. The geographic patterns of prey species consumed in our study reflect those in cities elsewhere. As the urban area changes, we predict that the densest populations of Red-tailed Hawks will continue to reside in the suburban areas where prey diversity and abundance are highest. This was one of the first studies to record urban Red-tailed Hawk diet and revealed patterns in how an urban population used food resources.