Male gorilla, Kiondo, October 2014

He's bulking up now after being long and lean for a while.

He's also quite badly plucked, particularly on his upper and lower arms. That's why he looks so grey, as you can see his skin. Compare with your other photo of 'Kivu'.

I was wondering why he looked so grey. Is hair plucking an issue with lowland gorillas in captivity?

Yes, though perhaps with better social groupings and management, not as much as in the past. Its almost always related to stress (possibly nervous-related). Some Gorillas suddenly develop the habit under a stressful situation, then stop it again completely when the stress that caused them to start disappears. Obviously once the habit has started, it can sometimes persist longterm though.

That's interesting. I've only known plucking to be endemic to the avian species. Never would have thought it extended into primates. Any worthwhile reading material on the subject you'd recommend?

I have always equated hair-plucking in Gorillas with feather plucking in e.g. Parrots. It is also found in Common Chimpanzees, Bonobos and some Monkey Species too- I have only rarely seen it in Orangutans. Another cause is over-grooming between members of a social group or a mother of her young. Presumably these two causes arise quite seperately from each other.

Have not come across any literature on it, but I am sure there must be some.