Only way I can figure (without a picture) for that sort of spot to be frostbite would be a drip of some sort causing a wet spot that gets bitten? Now, I don’t do winter… I’m not kidding when I say delicate west coast flower here, - anything F is torture IMO, so I thankfully don’t have much experience with this…Close to the head is unlikely to be frostbite. Is it possible he got fresh with one of the girls and she pecked him?