You might be able to quickly recognise a friend from afar based on their body language or their personal fashion choices. It turns out that some birds do the same thing, recognising familiar, harmless humans by their clothing.
Many birds have sharp memories, especially when it comes to keeping track of which humans are dangerous and which are harmless. Urban crows, for example, remember the faces of humans who have wronged them. Now, new research has revealed a more wholesome side of this birdy character judgment: shorebirds in China can distinguish humans based on their outfits and are less wary of people wearing the clothes and accessories of familiar, local fishers than those in casual attire.
Researchers from Hainan Normal University in Haikou, China noticed that on tidal flats in the Guangxi Zhuang Autonomous Region in southwestern China, birds would stand very close to local people fishing or digging for sandworms and snails. But when the onlooking researchers approached the birds, they’d fly away. It seemed as though the birds regarded the tide flat regulars as less of a threat than the visiting scientists.
So, the team decided to test whether or not the birds could tell the difference between casual and fishing outfits.
One of the researchers walked toward birds on the tidal flat dressed in either a “casual” outfit or one reminiscent of what local fishers were wearing—conical straw hats, tall boots, and tools. The team then recorded how close the researcher could get before the birds nope-d the hell outta there. They did this over 900 times.
This gave the researchers a “flight initiation distance”—how close a bird will let something approach before it flaps away—for eight different shorebird species. Many of these were small, plover-like birds, but there were gulls and egrets, too.
All species of shorebird were more unsettled (they flew away sooner) by the approach of someone in casual clothes than someone dressed to go fishing. These results—published recently in the journal Global Ecology and Conservation—suggest that the birds can differentiate between outfits and apparently judge humans with unfamiliar aesthetics as potentially more dangerous.
Some species were more sensitive to the researcher’s look. Black-headed gulls (Chroicocephalus ribibundus), for example, flew away at distances three times greater when approached by someone in casual clothes compared to fishing gear.
Constant exposure to fishers over years and years, write the researchers, may have allowed them to associate a lack of danger with the fishing outfits, since the humans would be engrossed in capturing aquatic creatures, not bothering the birds. Flying away when the danger is minimal wastes energy and time that could be spent finding food, so differentiating between threatening and benign visitors is a crucial skill.
“It’s interesting that [the birds] seem to have some degree of discrimination between humans with different outfits,” said Andrea Griffin, a behavioural ecologist at the University of Newcastle in Australia who was not involved with this research. “It hasn’t been shown before in shorebirds.”
Griffin points out that the birds—being highly visual animals attuned to the gaze of would-be predators—might be focusing on something other than the clothes themselves. The wide, conical hats of fishers conceal the wearer’s eyes, but casual attire does not. It’s possible simply keeping your eyes out of sight dampens the birds’ jumpiness.
“That means that a spontaneous response to frontally placed eyes is a real possible explanation for the difference they observed, so perhaps nothing to do with learning,” she said.
John Marzluff, a wildlife scientist at the University of Washington in Seattle also not involved with this research, said the differentiation of groups of humans by their clothes is a new one among birds.
“It’s the first time I’ve heard of this,” he said, noting however that there are some “anecdotal observations” of birds “keying in on what people hold, like a gun versus a broom.”
Marzluff said that the fishers’ attire stayed the same between each bird encounter, while the humans’ faces weren’t very visible. So the clothes were probably a more reliable indicator of each human’s relative threat level. This is unlike the situation in his own research with facial recognition in crows, where the clothes on specific humans change but their exposed faces don’t.
Marzluff said the findings help show that these types of threat recognition skills aren’t limited to brainier birds like crows and jays.
“You’re learning that a whole community of waterbirds—something that we don’t consider very smart, frankly—is also paying close attention to how we treat them,” he said, adding that research like this “tells us that birds are paying a lot more attention to us then than you would have ever thought.”