Citizen science provides an unprecedented glimpse into the diets of <i>Astur cooperii</i> (Cooper’s Hawk) and <i>Accipiter striatus</i> (Sharp-shinned Hawk)

Abstract Although Astur cooperii (Cooper’s Hawk) and Accipiter striatus (Sharp-shinned Hawk) are common and widespread, their diets have been poorly studied. Although some dietary datasets indicate both prey 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 has 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 A. cooperii and A. striatus diets, examining patterns of prey size and species preferences for each predator. Given that both species are known to prey heavily and, in some cases, primarily on birds, we hypothesized that the prey base observed for both species on iNaturalist would be largely avian; however, we suspected some mammals might also be consumed. Across 74,974 photographs of A. cooperii and A. striatus, we found 4,206 (6.79% of records) and 619 (4.75% of records) predation events for A. cooperii and A. striatus, respectively. After accounting for spatial heterogeneity in observation data, we found A. cooperii selected for Columbiformes, Colaptes auratus (Northern Flicker), and Passeriformes, with their most elected prey item matching their most observed prey item, Columba livia (Rock Pigeon). The smaller-bodied A. 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 A. cooperii and A. striatus are largely avian specialists, despite A. cooperii’s regular predation on small mammals.