City birds flew sooner from women. The reason is still unknown
flight initiation distance
The distance from a person when a bird starts to move away.
observer bias
A test result changes because of the person doing the test.
urban ecology
The study of living things and nature in cities.
What happened
An international team found a consistent pattern in urban birds. Birds usually flew sooner when a woman walked toward them than when a man did. The paper appears in People and Nature, a scientific journal about nature. In the study, the average flight distance was about one meter longer for women. Women could approach to about 8.5 meters before birds fled. Men could approach to about 7.5 meters.
This does not prove that birds feel a human emotion called fear. It measures a behavior. Researchers recorded the distance at which each bird moved away. They call this flight initiation distance, or FID. A longer FID means the bird left sooner.
How the study worked
The team watched birds in parks and other green spaces across seven cities. The cities were in Czechia, France, Germany, Poland, and Spain. The observations took place during spring 2023. The team recorded 2,701 approaches involving 77 species. For the main analysis, they used 2,581 records from 37 species with enough observations.
Female and male observers worked in pairs. They were matched as closely as possible for height and clothing. Each observer walked straight toward a relaxed bird at a steady speed. The team recorded starting distance, flock size, the bird’s sex, and nearby land cover. The analysis also accounted for differences among cities and bird species.
What the researchers could confirm
The pattern pointed in the same direction in all five countries. It also appeared across the group of 37 species. The study included common urban birds such as great tits, house sparrows, and blackbirds. The researchers also found that male birds generally allowed a closer approach than female birds. Yet both male and female birds tended to leave sooner when a woman approached.
These results do not mean that every bird reacts this way. They describe an average pattern under one set of conditions. The paper reports a statistically meaningful association after the researchers adjusted for several important variables.
Why it matters
A person walking toward a bird is part of the experiment. That person is not a perfectly neutral measuring tool. If observers of different sexes produce different bird responses, studies using only men or only women could measure different distances. This is a form of observer bias. It may affect research on urban ecology, wildlife disturbance, and how animals share cities with people.
The finding also shows why behavior can be harder to interpret than it looks. Birds may notice details that humans overlook. A study can control obvious differences, yet still miss a small cue that matters to an animal.
What remains unknown
The researchers do not know what birds are detecting. Possible clues include gait, body shape, hair, clothing, or scent. Height and clothing were made similar, but that does not remove every difference. The study did not test these clues one at a time. It therefore cannot identify a cause.
The result also does not show an inborn rule that birds everywhere use. The observations came from European urban areas, during a limited season and set of conditions. More locations and repeated experiments are needed.
What to watch next
Future studies could change one human feature at a time. They could compare walking style, hair, clothing, and scent. They could also repeat the work in other regions, seasons, and habitats. Until then, the strongest conclusion is narrow but useful: urban birds may distinguish between different human observers, and the observer can change the behavior being measured.
Why did city birds fly away sooner from women?
📰 Full story: City birds flew sooner from women. The reason is still unknown
A study found a strange pattern in birds living near people.
flight distance
How far a bird is from a person when it flies away.
observer bias
A person doing a test changes the result.
urban ecology
The study of nature and living things in cities.
💡 The gist
- Birds flew away sooner when women came near.
- The difference was about one meter.
- Scientists do not know which clue caused it.
What did scientists measure?
Scientists watched birds in city parks. They measured the distance when a bird flew away. This is called flight distance. A longer distance means the bird left sooner.
Women could get about 8.5 meters from birds. Men could get about 7.5 meters. So, birds left about one meter earlier when women came near. The team watched 2,701 bird approaches. The main test included 37 bird species.
The observations happened in five European countries. They included Czechia, France, Germany, Poland, and Spain. The researchers used seven cities. Women and men who walked toward the birds were matched closely. They wore similar clothes. Their heights were also similar. They walked at a steady speed.
Why might this happen?
Birds may notice small details about people. They might notice walking style, hair, body shape, clothes, or scent. The researchers tried to control some obvious differences. Still, the birds reacted differently. The team did not test each possible clue alone. So, nobody knows the cause yet.
The result does not mean all birds fear women. It describes an average result from this study. The study looked at city birds in Europe. Other birds may react differently in other places or seasons.
Why does the result matter?
A person is part of a bird experiment. The observer is not just a measuring stick. If women and men get different reactions, they may record different distances. This can create observer bias. Observer bias means the person doing the test changes the result.
This matters for urban ecology. Urban ecology studies living things in cities. Future studies should include different observers. They should also test one clue at a time. For now, the study gives scientists a new question. How do birds recognize the people near them?
Read the research paper for the full methods.
Birds flew away sooner from women
📰 Full story: City birds flew sooner from women. The reason is still unknown
Scientists watched birds meet people in city parks.
Scientists are people who learn about nature. They watched birds in five countries. The countries were in Europe. Europe is a place with many countries.
A woman walked toward a bird. The bird flew away. A man walked toward another bird. That bird waited a little longer.
Birds flew when women were farther away by about one metre. The team watched 2,701 bird approaches. They watched 37 kinds of birds.
The birds may have noticed walking styles. They may have noticed hair or clothes. They may have noticed smells. Nobody knows the real clue yet.
This does not mean every bird fears women. It was one study in city parks. Scientists will test the idea again. They will change one thing at a time. The birds may be noticing tiny differences.