Urban birds across Europe fly away sooner when approached by women than by men, according to a new study that leaves its own authors unable to explain the pattern they found.
Researchers sent male and female volunteers, matched for height and clothing, walking directly toward birds in parks and green spaces across Czechia, France, Germany, Poland and Spain, measuring how close each person could get before a bird took flight. On average, men could approach about a metre closer than women before 37 species of urban bird — including skittish magpies and famously tolerant pigeons — flew off. The pattern held consistently across all five countries and every species tested, drawing on 2,701 individual observations.
"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," said Professor Daniel Blumstein of UCLA, one of the study's authors, published in the British Ecological Society's journal People and Nature. Dr Yanina Benedetti of the Czech University of Life Sciences Prague said the finding challenged assumptions baked into decades of behavioural research. "Many behavioural studies assume that a human observer is neutral, but this wasn't the case for urban birds in our study."
Researchers have floated a handful of untested explanations, including pheromones, body shape or differences in gait, but say further experiments will be needed to isolate the actual cause. "This is maybe the most interesting part of our study," said co-author Dr Federico Morelli of the University of Turin. "We have identified a phenomenon, but we really don't know why."