Study finds city birds flee women more across 37 species

Federico Morelli and an international team of ecologists reported in May that urban birds across five European countries fled sooner when approached by women than by men, according to a study published in *People and Nature*. The researchers measured flight initiation distance, or FID — the point at which a bird takes off as a person walks toward it — across 37 species in city parks and green spaces. The paper said the gap was consistent across countries and species, with birds keeping about 1 meter more distance from women on average. The researchers said they do not yet know why. ### How did the researchers test this in city birds? The study, published with DOI 10.1002/pan3.70226, used paired male and female observers matched for height and clothing to approach birds in a straight line in urban settings across Czechia, France, Germany, Poland and Spain. The team then modeled the birds’ escape responses while controlling for other factors known to affect FID, including starting distance, flock size, vegetation cover, land use and the sex of the target bird. The paper said the researchers also accounted for phylogenetic relatedness among species using Bayesian regression models. That was intended to test whether observer sex still mattered after common drivers of escape behavior were taken into account. ### What exactly did they find across the 37 species? The researchers said the effect held across all 37 species in the sample, from birds that usually flee early, such as magpies, to species that tend to tolerate people more closely, such as pigeons. The average difference was about 1 meter, with birds allowing men to come closer before taking flight. The study also found that male birds were more risk-tolerant than female birds. But the paper said the most unexpected result was the observer effect: birds in general escaped sooner when approached by women than by men. ### Did the pattern show up only in one country or one type of bird? The British Ecological Society said on May 13 that the result was consistent across all five countries in the study. The paper’s abstract likewise said the longer escape distance around women appeared in populations across each of the five countries examined. Daniel Blumstein, a University of California, Los Angeles ecologist and co-author, said the consistency across cities and species strengthened the result even though the mechanism remains unclear. “I fully believe our results,” Blumstein said in comments released with the study, adding that the team did not yet have a conclusive explanation. ### What do the researchers think birds might be reacting to? Yanina Benedetti of the Czech University of Life Sciences Prague said she was surprised by the finding as a woman doing fieldwork. In comments released by the British Ecological Society, she said the study showed that urban birds respond to human observers in ways many behavioral studies treat as neutral. Federico Morelli of the University of Turin said the team had identified a real pattern but not its cause. The researchers listed possible cues including pheromones, body shape and gait, but they described those ideas as speculative and said more work is needed to test them directly. ### Why does flight initiation distance matter in the first place? Flight initiation distance is a standard measure in behavioral ecology because it captures how animals balance risk against the costs of fleeing too early. A longer FID generally indicates greater wariness, while a shorter one suggests greater tolerance of an approaching threat. The paper said that distinction matters in cities, where birds encounter people constantly and must repeatedly decide when to stay put and when to leave. The next step, Benedetti said, is to isolate specific cues such as movement patterns, scent signals or physical traits in follow-up studies rather than treating observer sex as a single bundled factor.