What is that thing on my chicks' rump?

[gypsymoonfarm]

I was playing with my chicks a minute ago and I notice directly above each one's tail is a growth. It does not contain a feather. It looks like there should be a pin feather growing out of it. All three of my new porcelain d'uccle chicks have it. It is only noticeable on one chick, I had to look at the rest of their behinds closely to see it.

 

[Tres Amigas]

I'm no avian vet (although I did stay at a Holiday Inn last night), I believe chickens have an oil gland right in that area. They get oil from it on their beak and then preen their feathers with it.
Oh, and

 

[ScissorChick]

Its the oil gland.

I remember a couple years ago I was handling a chick and noticed it. I thought it was some

weird growth.

ScissorChick

 

[gypsymoonfarm]

Thanks! I've seen my older chickens pick that area often but I've never inspected what they were picking at. It makes sense now.