Birds living in cities are more scared of women than men, a study has found.
Scientists have established that men are able to get within 7.5m of urban birds before they take flight, a full metre closer than women.
The results were consistent across five countries and 37 different species of birds, including some, such as magpies, known to be more nervous of humans, and others, such as pigeons, which are less easily spooked.
The reason women are more intimidating to avians than males remains unknown. Researchers initially thought the evolutionary or corporeal difference between men and women might be responsible, but the study found that neither the height of the women nor the length of their hair changed the results.
Study co-author Dr Federico Morelli, from the University of Turin, said: “We have identified a phenomenon, but we really don’t know why.”
The scientists set out to determine whether the fight-or-flight response of urban birds depended on the gender of the person approaching them.
They had anticipated that the birds would view men as more threatening based on early human history when males were primarily hunters and women gatherers.
To test their theory, male and female pairs of similar builds were dressed in the same colour and walked in a straight line towards birds in parks and green spaces, looking directly at them as they approached.
The experiment was carried out on 2,701 separate occasions in the Czech Republic, France, Germany, Poland and Spain.
The study, published in the British Ecological Society journal People and Nature, found that men were able to get closer to all species, but that some were more jumpy than others.
Pigeons tended to allow people within 3.5m, while long-tailed tits, one of the smallest birds in the UK, let people come within 3.6m before taking flight.
More wary species included magpies, which took off at 13m on average, and green woodpeckers, which fled at 16.2m.
The researchers suggested differences in smells, body shape or gait may provide answers about why birds fear women more than men, but stressed that any theories are speculative.
Another possible explanation put forward is that women who hunted in early societies were more likely to target smaller prey such as birds, while male hunters focused their efforts on larger animals.
Co-author, Prof Daniel Blumstein, from the University of California, Los Angeles, added: “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.
“There are several possibilities for what cues birds are picking up on. It could be smells, it could be people’s gait.”
The researchers concluded that birds’ heightened fear of women indicates their “sophisticated evaluation” of their environments and how “subtle differences” in their human surroundings could influence their reactions.