Despite being common and widespread, the diets of Astur cooperii (Cooper’s Hawk) and Accipiter striatus (Sharp-shinned Hawk) have been poorly studied. Although some dietary datasets indicate both feed heavily on birds, most studies have focused on nest site or bird feeder observations, thus precluding comprehensive assessments of the species’ diets. Recently, increased popularity in citizen science programs like iNaturalist and eBird have allowed an unprecedented glimpse into the ecology of both species that may allow dietary analyses. Herein, we used iNaturalist, a photograph-vouchered citizen science platform, to perform an assessment of Astur cooperii and Accipiter striatus diets, examining patterns of prey size and species preferences for each predator. We hypothesized that both species would feed primarily on birds, however, we suspected some mammals might also be selected for. Across >70,000 raptor observations, we found 4,206 (6.79% of records) and 619 (4.75% of records) predation events for Astur cooperii and Accipiter striatus, respectively. After accounting for spatial heterogeneity in observation data, we found Astur cooperii selected for Columbiformes, small Galliformes, Colaptes auratus (Northern Flicker), and invasive Passeriformes, with their preferred prey item matching their most observed prey item, C. livia (Rock Pigeon). Despite their proclivity for avian prey, Astur cooperii also fed on mammals, selecting heavily for Rattus norvegicus (Norway rats). The smaller-bodied Accipiter striatus preferred small Passeriformes, though Columbiformes were also selected for. Both species exhibited bimodal prey size selection, likely driven by differential use of Columbiformes and other prey items. Collectively, these data support the hypothesis that Astur cooperii and Accipiter striatus are avian specialists, despite Astur cooperii’s regular predation on small mammals.
Assessing cooper’s hawk (Astur cooperii) and sharp-shinned hawk (Accipiter striatus) prey size and species composition using citizen science data
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