Domestic cat density is not associated with variation in avian risk assessment in a mega-city

Abstract Domestic cats ( Felis catus ) kill an estimated 1.3–4.0 billion birds annually in the United States and are a major source of mortality for urban birds. While their lethal impacts are well documented, fewer studies address sublethal effects such as changes in avian risk assessment. We analyzed a dataset of 1,120 experimental approaches by human observers on 48 bird species across 11 sites in the Los Angeles metropolitan area, which varied in free-roaming cat and human population densities. Using Bayesian mixed models, we examined ecological and intrinsic predictors of avian flight initiation distance (FID). At the community scale, cat and human population densities had no significant effects on FID, suggesting that predator and human presence may already exceed a threshold across the urban landscape beyond which additional variation does not produce detectable changes in avian escape behavior. Species-specific analyses revealed that black phoebe ( Sayornis nigricans ) FID increased with human population density. We found no community-level interaction effect of human density and cat density, but house finches ( Carpodacus mexicanus ) and rock pigeons ( Columba livia ) tolerated closer approaches in areas with both high human and cat density, suggesting that habituation to humans may lower perceived predation risk for some urban species. Heavier species, ground-foraging individuals, and actively foraging birds had shorter FIDs. Birds also flushed at greater distances as the time of day progressed. These results highlight the complex interplay of intrinsic and environmental factors shaping avian escape behavior and underscore how behavioral adaptation in megacities may alter predator–prey dynamics in urban landscapes.