Chickens Bleeding From Head

Hi Everyone

I noticed on the hanging feeder in my chicken coop that there is dried blood around the feeder from when the chickens were feeding. Problem is I cant tell which one of them is bleeding because they are brownish color. Could it be that they have frostbite on their wattles (sp?). I put Vaseline on them, not very often though. It seems they start to peck at each other's wattles when I put Vaseline on. Any suggestions?

Thank you!