Birds living in cities appear to react differently to men and women, and scientists are struggling to explain why. An international research team discovered that urban birds, including great tits, house sparrows, and blackbirds, tend to fly away sooner when approached by women than by men. The surprising behavior raises new questions about how birds perceive the people around them.
The study took place in five European countries, where male and female participants (matched for height and clothing) walked directly toward birds in city parks and other green spaces.
On average, men were able to approach about one meter closer than women before the birds flew away. The researchers measured this response by recording how close a person could get before a bird took flight (termed flight initiation distance).
Published in the British Ecological Society journal People and Nature, the findings showed the same pattern in Czechia, France, Germany, Poland, and Spain. The difference also appeared across all 37 bird species examined, including easily startled magpies and pigeons that typically allow people to approach much more closely.
Why Are Birds More Afraid of Women?
The researchers believe their findings indicate that city birds can distinguish between male and female humans. However, they have yet to determine which characteristics the birds recognize or why they appear more cautious around women.
Professor Daniel Blumstein of the University of California, Los Angeles, who helped conduct the research, said the results were convincing despite the lack of an explanation.
“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. We used bleeding-edge comparative analysis techniques that showed our findings were consistent across cities and species, but we simply don’t have a conclusive explanation yet.”
Dr. Yanina Benedetti of the Czech University of Life Sciences Prague, another member of the research team, said the discovery challenged her expectations about how birds respond to human observers.
“As a woman in the field, I was surprised that birds reacted to us differently. This study highlights how animals in cities ‘see’ humans, which has implications for urban ecology and equality in science. Many behavioral studies assume that a human observer is neutral, but this wasn’t the case for urban birds in our study.”
What Are Birds Detecting in Humans?
Scientists have proposed several possible explanations for the difference. Birds might be responding to chemical signals such as pheromones, variations in body shape, or differences in how men and women walk. For now, however, these ideas remain speculative, and additional experiments will be needed to identify the actual cause.
Dr. Federico Morelli of the University of Turin, a co-author of the study, said the unanswered question is one of the discovery’s most fascinating aspects.
“This is maybe the most interesting part of our study,” said Dr. Federico Morelli from the University of Turin, a co-author of the study. “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.”
The findings suggest that urban birds may be sensitive to human characteristics that people themselves rarely notice. Identifying those signals could help researchers better understand how wildlife assesses potential threats in environments shared with humans.
Dr. Benedetti said: “Urban birds clearly react to subtle cues that humans do not easily notice. Follow-up studies could focus on individual factors such as movement patterns, scent cues, or physical traits, testing them separately rather than grouping them under observer sex. This approach would help identify the specific cues birds detect.”
More Research Is Needed to Explain the Bird Behavior
Although the investigation included 2,701 observations, the researchers emphasize that their findings are still preliminary. Further studies will be necessary to establish whether the difference between birds’ responses to men and women consistently appears in other settings and populations.
For now, the discovery points to an intriguing possibility: Birds sharing our cities may be paying attention to subtle differences between people that scientists have yet to fully understand.
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