Urban Birds Appear to Fear Women More Than Men, But Why?

Male birdwatchers may have an unexpected advantage when sneaking in for a close-up in a city park.

Scientists were recently surprised to find that dozens of common birds in Europe are more ruffled by the approach of a woman than a man.

In experiments in France, Germany, Poland, Spain, and Czechia, researchers found that urban birds 'chickened out' sooner when a woman strolled toward them.

They let men come roughly one meter closer, on average, before flying or wandering off.

"As a woman in the field, I was surprised that birds reacted to us differently," says ecologist Yanina Benedetti from the Czech University of Life Sciences Prague.

"Many behavioral studies assume that a human observer is neutral, but this wasn't the case for urban birds in our study."

Blackbirds, robins, starlings, finches, crows, sparrows, magpies, ducks, jays, woodpeckers…

The species didn't seem to matter. They all showed this male bias.

"This is maybe the most interesting part of our study," says biologist Federico Morelli from the University of Turin in Italy.

"We have identified a phenomenon, but we really don't know why."

Humans and birds in Europe have lived in close proximity for tens of thousands of years, and for a long time, researchers thought that in the distant past, men were the hunters and women were the gatherers.

If that was the case, however, then why did birds in Europe seem less wary and more tolerant of men? Is it possible that ancient women were hunting these smaller prey more?

"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," says conservation biologist Daniel Blumstein from the University of California, Los Angeles.

"We simply don't have a conclusive explanation yet."

Bird watchers on the lookout. (John Rowley/Digital Vision/Getty Images)

At this point, all we can do is speculate. Researchers don't even know how birds can tell the difference between human sex and/or gender.

The study compared male and female observers, but it's unclear if the birds are responding to physiological differences between the sexes or reacting to gender-associated cues.

However, the researchers did make some attempts to limit differences in appearance and approaches.

For each observation, a pair of male and female participants, of roughly the same height and dressed in the same colors, approached a bird.

They would also take turns being the first one to approach. Each observer would walk toward the bird, 'as the crow flies', at a normal and constant speed. Their head and eyes were to remain fixed on the avian, no 'swanning' around.

Female observers did not partake in the study while menstruating, and if they had long hair, it had to be tucked away.

Researchers analyzed more than 2,000 approaches, covering 37 bird species in total. The birds appeared to be picking out subtle differences between the approaching humans.

"Urban birds clearly react to subtle cues that humans do not easily notice," says Benedetti.

"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."

In the past, birds were not thought to have a great sense of smell, but recent evidence has refuted that idea. Turns out, many birds have powerful olfactory systems. So it's possible that they are 'smelling' the sex differences of an approaching human.

Lab mice, for instance, are known to be sensitive to the different smells of men and women. A little over ten years ago, scientists discovered that these rodents experience greater stress when handled by men.

Similar stress responses to the human male sex have also been observed in domesticated animals, such as horses and cows, and captive animals including monkeys.

This new research among birds is some of the best evidence yet for similar behaviors in the wild. But it turned up the exact opposite outcome.

Related: Birds Have a Mysterious 'Quantum Sense'. For The First Time, Scientists Saw It in Action

"This study highlights how animals in cities 'see' humans, which has implications for urban ecology and equality in science," says Benedetti.

A birder in a city park might think they are the only ones doing the observing, but they would be wrong.

The study is published in People and Nature.