Domestic Cat Density is Generally Not Associated with Variation in Avian Risk Assessment in a Mega-City

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 conducted by human observers on 48 bird species across 11 sites in the Los Angeles metropolitan area, which vary in free-roaming cat and human population densities. Using Bayesian mixed models, we examined ecological and intrinsic predictors of FID. At the community scale, cat and human population densities had no significant effects, suggesting that urban birds in Los Angeles may be tolerant to human and cat presence, potentially masking effects seen in less densely populated areas. Species-specific analyses, however, showed that house finch ( Carpodacus mexicanus ) FID was positively associated with human density while house sparrow ( Passer domesticus ) FID was positively associated with cat density. Bird height above ground was positively associated with human density, possibly reflecting increased vigilance in response to humans. Larger-bodied birds, ground-foraging individuals, and actively foraging birds had shorter FIDs. Time of day also influenced responses, with birds flushing at greater distances and perching higher as the day progressed. These results highlight the interplay of environmental and species-specific factors in shaping avian escape behavior and underscore the role of behavioral adaptation in urban ecosystems, with implications for understanding predator–prey dynamics and guiding conservation in human-dominated landscapes.