Key takeaways
- An international study of how human behavior affects urban birds' anti-predator reactions found that men can get about three feet closer than women before birds flee.
- The study is the latest to find animals recognize differences in men and women, suggesting studies with all-male or all-female experimenters could obtain biased results.
- Scientists controlled for size, clothing, hair and many other factors of the researchers who approached the birds.
- More study is needed to learn how and why birds react to different sexes.
Why are Redditors obsessed with an international birding study? Because scientists found that city birds seem more afraid of women than men. The researchers don't know why (yet), but it could bias the results of studies that don't include female scientists, said UCLA behavioral ecologist and conservation scientist Dan Blumstein, a co-author of the study.
Researchers studying the effects of human behavior on urban birds found that men could get about three feet closer to birds before the animals fled than women could. According to their findings, published in the British Ecological Society journal, the results held true for more than 2,500 birds from 37 species, and across seven European cities in France, Germany, Spain, Poland and the Czech Republic. From pigeons to crows, robins to blackbirds, all were quicker to flee from women than men.
Birds aren't the only animals that react differently to men and women, the study noted. In 2014, a team found that lab rats and mice were more stressed when handled by men than women. Monkeys and dogs also played favorites, according to researchers in 2013 and 2023 respectively. But this is the first time scientists saw different reactions in birds, said Blumstein, a professor of ecology and evolutionary biology and a member of the UCLA Institute of the Environment and Sustainability.
"I trust our results, but we don't know why it's happening," Blumstein said. "Part of what this tells us is that the sex of the experimenters could affect the results of an experiment. In theory, that could be a source of bias in an experiment that researchers need to control for."
Months after the study's publication, it's prompted online debate, with those on social media guessing how birds recognize women vs. men. Could it be height? Long hair? Bright clothing? Thanks to the design of the experiment, the researchers concluded that none of those are factors. In each city, one woman and one man — both expert ornithologists — were paired up to approach birds from similar distances at a slow pace. The ornithologists were similar in height and weight. They wore similarly colored clothing. If only one member of a pair had long hair, they hid it.
The researchers were originally interested in learning more about birds' anti-predator behavior related to topics like eco-tourism or urban-rural differences.
"We went in trying to find out more about how birds see the world, and it really expanded what we know about how birds see us," Blumstein said. "We know birds can identify individuals, and this suggests they can distinguish sex."
Previous experiments have shown that birds react differently to humans and predators depending on various factors. Approaching faster, or coming with or even from a group, makes birds edge away sooner. In this case, with the experiment controlling for those elements, the birds could be recognizing differences in how people walk, Blumstein said, noting gait is influenced by biological differences in male and female pelvic structures.
"We didn't expressly control for how people walked, but our experimenters certainly didn't exaggerate it," Blumstein said.
It's possible that birds are using smells or hormones to tell the difference between men and women — although the distances involved make Blumstein think that's unlikely. Because birds can see in the UV range, it could be related to sunscreen and makeup containing sunscreen, a Reddit theory Blumstein thinks is worthy of a formal test.
"In science, a good question will often lead to results that raise even more questions," said Blumstein. "Bottom line — this is an open niche for more studies."
Using a database of hundreds of other studies that include calculations of how close scientists got to over 150,000 birds before the animals took flight, Blumstein and his colleagues hope to learn more soon.
