Black Necrotic Skin Tissue - Cause?

[Scuiry]

I have a pigeon that has developed black necrotic tissue around the neck. It's left foot is also turning black. The skin texture is leathery and thick. Feathers are still intact around the neck and crop area. Slightly distended in front of the neck.

Is there some parasite, vitamin deficiency or systemic disease that could cause this?

Pigeons seems to be in no pain or distress. Favors foot that is turning black but does not appear to be in any discomfort. Droppings have decreased dramatically (almost zero).

Daniel