So... I've been lurking (because that's what I do haha) but I had a first thought when this thread went up that I haven't seen anyone mention.
Chickens don't have sweat glands, but do chickens have oil glands? I know they have a preening gland, but do chickens secrete oils from their skin, like mammals do?
It looks kinda like a cluster of clogged pores/glands to me... but again, take that with a grain of salt, as I know absolutely next to nothing about chicken health - just tossing that out there because I hadn't seen anyone else ask (probably for a reason

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