Why Do So Many Urban Pigeons Have Missing Legs Or Feet?
If you live in a town or city with a large feral pigeon population then you’ve probably noticed that a relatively high proportion of them have deformed or missing legs and feet.
For years the most common theory put forward was that pigeons’ own poo was the cause. The accumulation of pigeon droppings is known to damage masonry due to the high acid content acting like a corrosive, with buildings constructed from limestone or sandstone particularly vulnerable. For example, it is well document that the monuments in Trafalgar Square where thousands of pigeons used to gather until measures were put in place to deter them, received extensive damage from pigeon droppings. Nelson’s Column was repaired from years of damage at a cost of £140,000.
Pigeon poo to blame
The theory went that if pigeon poo was acidic enough to corrode buildings then it could do the same damage to their feet. With flocks of pigeons living so closely together in relatively small spaces it was inevitable that they would spend much of their time standing in their own excrement. Although this may explain why pigeons have missing toes, it doesn’t make sense that pigeon droppings would cause an entire leg to fall off.
Another idea also blamed pigeon poo. As well as its corrosive effects, pigeon droppings are full of bacteria which can cause disease. Standing in their own poo means pigeons are susceptible to these diseases and if an infected foot or leg develops gangrene, then part of it may fall off. But most diseases of the feet such as bumblefoot or avian pox cause deformities or tumours rather than amputation. So even if pigeons do catch diseases from standing in their own poo then it’s probably not the cause of their missing limbs.
In 2018 researchers in Paris conducted a study on 1,250 pigeons across 46 sites and came up with a new theory. The team from the Centre for Ecology and Conservation Science discovered that 20% of the pigeons they looked at were missing at least one toe. They found that pigeons were more likely to have mutilated feet in areas where air and noise pollution was high and where the human population was densest.
Thriving in the city
But they also found that if there were a large concentration of hairdressers there was a higher chance that pigeons had lost their toes. The scientists concluded that the high movement of traffic and people would transport hair strands around the city and as the pigeons walked about their legs were getting tangled in human hair as well as other materials such as plastic rubbish bag ties or bits of thread.
When the birds try to remove the hair or string with their beaks, they are unable to and in fact pull it tighter around their toes or legs, restricting the blood flow, which causes the toe or the leg to fall off.
So how do pigeons get on with missing limbs? Outside of cities one-legged birds would struggle to survive as they are susceptible to predators, but in the densely populated areas where you find large flocks of feral pigeons they have surprisingly few predators. And therefore, despite the fact that the urban environment is tough for any wild animal, pigeons with missing feet or legs are able to survive for much longer than they would elsewhere. Peregrine falcons and sparrowhawks will take pigeons as will rats and even pelicans, but feral pigeons are relatively free from the risk of being predated.
Missing legs and feet can make it harder for birds to find food sources, but living as they do so close to people, there is an abundance of food for pigeons on the streets around them from discarded takeaways to human vomit. Again, outside of cities birds with amputated limbs would find it hard to survive.
One effect a missing limb may have is on reproduction success. A male pigeon with just one leg will find it difficult to balance on the female during copulation. Pigeons with missing limbs may also find it harder to scratch and groom themselves so they end up looking pretty scruffy, which not only makes them less attractive to potential mates, but can also affect their health as they’re unable to get rid of parasites such as ticks and feather mites.