Women Trigger Stronger Fear Response in European Urban Birds

A study of urban birds in five European countries found that female humans consistently triggered a larger flight response than male humans. Across 36 species—including the European Great Tit, magpies and pigeons—men could approach to within about one meter before birds fled, whereas women prompted flight from a greater distance. The pattern persisted regardless of observers' clothing, height or approach style, suggesting birds detect human sex via unknown cues.

Scientific American

The authors reference mammalian work showing sex-based stress differences—laboratory rats stress more when handled by male than female researchers—indicating animal sex discrimination is plausible. The study was led by Daniel Blumstein, professor of psychology at UCLA, and Federico Morelli, associate professor of ecology at the University of Turin, who designed the field protocol, oversaw data collection across multiple urban sites, and contributed to analysis.

Scientific American

The researchers surveyed 36 bird species in urban centers of five European nations. Across all species, men approached to within roughly one meter, while women caused birds to flee from a larger distance. Clothing, height and approach style did not affect the outcome.

Scientific American

The findings reveal a previously undocumented aspect of human-bird interaction, showing that urban birds assess subtle human traits when judging risk. Recognizing such cues could guide urban wildlife management and public advice on coexisting with city birds.

Scientific American

Blumstein expressed confidence in the pattern but said its cause remains unknown. Morelli described the observation as evidence of sophisticated environmental evaluation by birds and noted that explanations such as chemical signals or visual cues are speculative.

Scientific American

Critics note the study’s inability to pinpoint the mechanism, leaving a clear knowledge gap: the specific cue enabling birds to differentiate male from female humans has not been identified.

Scientific American

• “I fully believe our results, that urban birds react differently based on the sex of the person approaching them, but I can’t explain them right now.” — Daniel Blumstein, Professor, UCLA

Scientific American

• “We have identified a phenomenon, but we really don’t know why. However, what our results do highlight is the birds’ sophisticated ability to evaluate their environment.” — Federico Morelli, Associate Professor, University of Turin

Scientific American

• “It could be smells, it could be people’s [gait]. But how do we test this? Perhaps a study resembling Monty Python’s Ministry of Silly Walks.” — Daniel Blumstein, Professor, UCLA

Scientific American

• “The outsize fear response to women was consistent across the species.” — Scientific American article

Scientific American

The team plans experiments isolating olfactory cues and gait variations to test which, if any, serve as reliable sex indicators for birds, aiming to clarify the sensory mechanism behind the observed behavior.

Scientific American