pekin ducks have bump on bum

[katie_]

my pekin ducks are about a week old and doing great but I noticed they are all picking at their tail there’s a little bump. I don’t know if it’s just a feather coming in already or maybe something with they’re gland. anyone have any ideas? all 4 of them have something similar in the same spot

 

[sourland]

It's their oil gland. They rub their bills on it and then oil their growing feathers - perfectly normal.