"Many pigeons have bad feet because in the end, bad feet, missing toes, do not kill them or cramp their style. If, say, female pigeons (which, by the way, are also susceptible to limb loss) refused to mate with crippled males, then we would see pigeons evolve the kind of feet that are tough enough to deal with hair, string, shit, and predators. But that has not and may not ever happen. So even if a pigeon is missing all of its toes, it can still eat, still get around the city, and still do the dance that gets it laid and paired for life."
Mudede, Charles. "Why Are Pigeons’ Feet So Fucked Up?" The Stranger. 21 August 2013.