Many women are afraid of birds. Birds are, too. City-dwelling birds were found to fear women more than Namsung. Birds fled faster when a woman approached. Previous studies also found that laboratory animals showed different responses depending on a researcher's sex. Scientists do not yet know why, but they think animals can, in some way, tell men and women apart.
The British Ecological Society said on the 28th (local time) that "scientists in the United States and Europe observed birds living in cities in five countries and confirmed that their avoidance behavior differs depending on a person's sex." The findings were published in the international journal "People and Nature." The society said this is the first study to test whether an observer's sex influences birds' flight behavior.
◇ whether they flee early or late, all avoid women
Pigeons, magpies and sparrows living in urban parks peck leisurely at food but move away or fly off when people come close. The team ran an experiment in which male and female participants of similar height and clothing walked straight toward birds in urban parks or green spaces. In the experiment, Namsung could approach on average 1 m closer than women before the birds fled.
This pattern appeared consistently across five countries, including France, Germany, Spain, Poland and the Czech Republic. And from species like magpies that avoid people more quickly to species like pigeons that flee later, all 37 urban bird species studied showed the same pattern. Based on the results, the team concluded that city birds can recognize the sex of people approaching them.
They did not pinpoint which human traits birds use to detect sex or why they fear women more. Federico Morelli, a professor in the Department of Life Sciences and Systems Biology at the University of Turin, Italy, and the paper's corresponding author, said, "We confirmed a consistent pattern, but we still don't know exactly why," adding, "However, these findings show that birds have the ability to finely perceive their surroundings, including people."
The team suggested birds may distinguish body odor, gait or body shape between men and women. Yanina Benedetti, a postdoctoral researcher in the Department of Applied Geoinformatics and Spatial Planning at the Czech University of Life Sciences and a co-author, said, "Going forward, we can focus on individual factors such as behavioral patterns, scent signals and physical characteristics and test each separately."
If the experiment had been conducted only with female observers, it would have found that birds fled even faster than when both men and women participated. The results show the need for a balanced sex ratio in scientific research. Dr. Benedetti said, "As a female researcher, I was surprised that birds respond to us differently," adding, "This study shows how urban animals perceive humans, and it has major implications for urban ecology and equality in science."
◇ researchers' sex also affects laboratory animals
The study aligns with earlier findings that experimental outcomes change depending on the sex of researchers or laboratory animals. Like urban birds, laboratory animals also distinguished a researcher's sex. Jeffrey Mogil, a professor of psychology at McGill University in Canada, reported in 2014 in the international journal "Nature Methods" that the pain response of lab mice dropped 40% when a Namsung researcher was present compared with when a female researcher was present. That makes it harder to accurately gauge pain response in drug tests.
Mice feeling less pain is due not to comfort but to a sharp rise in corticosterone, a stress hormone. Whether human or animal, when facing danger they trigger stress to block pain themselves. Mice perceived a Namsung researcher as a predator-like risk factor. When male and female researchers were together, the lab animals' stress responses were offset.
In science, balancing the sex ratio of laboratory animals also matters. In the past, life science studies mostly used male lab animals. The reason given was that females' hormonal fluctuations during estrus could easily affect experiments. That can lead to fatal consequences. From 1997 to 2000, 10 drugs were withdrawn in the United States for deadly side effects, and 8 of them had more adverse effects in women. Using both sexes evenly at the animal-testing stage could have prevented this.
Fortunately, recent scientific research is trending toward balancing the sex ratio of lab animals. A Northwestern University team reported in 2020 that the number of papers using both sexes in animal experiments doubled over a decade. It was also shown that sex bias in lab animals lacks scientific basis. A Harvard Medical School team reported in 2023 in "Current Biology" that "in experiments exploring new spaces, the behavior of female mice was more stable than that of males, regardless of hormone levels."
References
People and Nature (2025), DOI: https://doi.org/10.1002/pan3.70226
Current Biology (2023), DOI: https://doi.org/10.1016/j.cub.2023.02.035
eLife (2020), DOI: https://doi.org/10.7554/eLife.56344
Nature Methods (2014), DOI: https://doi.org/10.1038/nmeth.2935