The team from the National Museum of Natural History and the University of Lyon recorded the occurrence and extent of toe mutilations from pigeons eking out their time in 46 sites across Paris.
They found that human pollution likely played a part in nearly all cases of missing toes and that pigeons living in areas with higher rates of air and noise pollution tended to have fewer digits than those that lived in leafier environs.
Perhaps most strikingly, the team noticed that toe mutilation “tended to increase with the density of hairdressers” – suggesting the birds often lose their extremities by getting them entangled in human hair.
We need to work out causation here. More hairdressers means shorter human hair out on the street, no? Less being left to float around the streets, certainly.
Thus, more likely, there are more hairdressers in tighter urban environments, the tighter urbanity causing the toe loss.