[blakestyger]

In Cambridge yesterday I saw a pigeon eating some dropped chips in Rose Crescent - not unusual these days except that this bird had not one single toe.
All had gone - front and back - both feet. Yet he was able to caper about on his little round stumps and appeared to be functioning normally; he couldn't perch on a wire, obviously, but pigeons are natural cliff dwellers and the city affords plenty of ledges.
I've also noticed that many gulls appear to have only one leg as do many waders. This latter may be seen on the beach or mudflats when they move from rest - some roost on one leg and they can walk/run but the 'unidexters' can only hop.
Does any one know why foot/limb loss is so common amongst birds?

[RD]

Birds can lose feet as a result of being entangled in fishing line.
It forms a tourniquet, cuts off the blood supply, and the foot becomes gangrenous and drops off.

Apparently, on the rehab center's first attempt to capture Stubby, they had witnessed the amputated foot wrapped in fishing line trailing behind the bird. The fishing line had strangulated the leg and caused it to become necrotic and fall off.

http://www.jphilarnold.com/exxfriends/forum_posts.asp?TID=1686&get=last

Another explanation would be frostbite, e.g. if the pigeon perched on a metal wire rather than tree branch in cold weather.
[metal has better thermal conductivity than wood]. 

[Flyberius]

I was always told it was from them walking in there own poo. They literally rot off.  Makes sense as there are few fishing lines in London yet plenty of poo and plenty of toe-less pigeons.

[RD]

Fibres other than fishing line would suffice...
http://en.wikipedia.org/wiki/Hair_tourniquet

[chris]

Perhaps a diet of too many chips has caused the pigeon to develop peripheral vascular disease and its toes have dropped off due to arterial insufficiency...?

[LeeE]

I believe that at one time it was regarded as very dangerous to eat London's pigeons due to a build up of various toxins in them (I think this also applied to vegetables grown in the inner city).  IIRC, the Lead levels were very high, but there were a number of other dangerous toxins too.  The Lead problem would apply to any city that had an appreciable level of motor traffic but industrial cities will have had the other toxins as well.

It's possible that these toxins lead to genetic mutations, such as losing toes, which may not have been a disadvantage and might have actually conferred an advantage, to city dwelling pigeons (where they spend a lot of time of the ground or on ledges and don't need toes) due to the reduced surface area of the feet helping reduce heat loss during cold winters when food is scarcer.

[blakestyger]

Yes - to lose accidentally (or even to disease) all toes, front and back, doesn't seem likely. I've seen partial loss in London birds but a genetic link is interesting; I'll look out for some more birds like this next time I go.

[blakestyger]

Quote: I was always told it was from them walking in there own poo. They literally rot off.

This would surely translate into seabird colonies where they sit on poo yea deep - especially those birds responsible for all that guano in S America?