Tolerance and avoidance of urban cover in a southern California suburban raptor community over five decades

We explored nest site placement and re-use relative to ornamental tree usage and urbanization level in a diurnal raptor community in southern California (USA) during three discrete time periods spanning five decades (1971-2018). Re-use of prior years' nests varied among species, with Red-tailed Hawks (Buteo jamaicensis) and American Kestrels (Falco sparverius) showing moderate re-use rates (ca. 30%), and Red-shouldered Hawks (Buteo lineatus), and Cooper's Hawks (Accipiter cooperii) showing almost none. Nearly all nests were in native and naturally-occurring trees during the 1970s, yet by 2018, most Cooper's Hawk nests, and many Red-tailed Hawk nests, were located in ornamental vegetation such as pines (Pinusspp.) and eucalyptus (Eucalyptusspp.). The amount of urban cover around nest sites increased for Red-tailed, Red-shouldered, and Cooper's hawks during the study period, but not for American Kestrels, which were confined to the least-urban areas. Cooper's Hawks appear to now be selecting urban nest sites over wildland sites, based on the increase in surrounding urban cover, even as landscape urbanization has not substantially changed in the study area during the last two time periods. Our study illustrates the utility of long-term datasets in understanding how a species' urban tolerance can change over time, and highlights species (including three extirpated taxa) that may be failing to adapt to local urbanization.

Automated summary

In a diurnal raptor community in southern California, nest site re-use varied among species, with some species showing moderate re-use rates while others showed almost none. Over time, nests began shifting from native vegetation to ornamental trees, and an increase in urban cover may be influencing some raptor species to select urban nest sites.