Congeneric predators fill discrete niches created by the relative abundances of their prey species

To what degree is niche partitioning driven by underlying patterns in resources such as food, rather than competition itself? Do discrete niches exist? We address these questions the context of Cooper's and sharp-shinned hawks, two broadly sympatric, North American, bird-eating raptors genus Accipiter. find that resource base, quantified body masses birds at bird feeders, approximately lognormal (smallest are most abundant), with lesser modes (peaks) abundance larger mass. The predators appear to exploit peaks hawks focusing on small prey items (median 26.5 g), taking from abundant (both mass peak a medium ~90 g). tested ability citizen scientists distinguish notoriously similar species, we determined influence potential false positive detections our conclusions. struggle one another, 18% were identified while 27% hawks. Yet, simulations show this uncertainty did not jeopardize qualitative