swolen finger, yellow, dry, no wound

by Emmil
(Jonggol,Indonesia)

Please see this photo first: (link didn't work)
The long back finger of the left foot of my lovebird is swollen, but the swollen part looks yellow, not red, not wet. It seems that the outer gray skin has been peeled off but no wound was found. Questions: What has caused it? Is it because of getting bitten since he lives in a colony cage and has a girlfriend? What kind of treatment should I apply to his finger?

Note: Except for his swollen finger, he's healthy but now he has started to lift his left foot when he's standing. He's in a quarantine cage now.

I appreciate any thoughts. Thanks for helping!