Duckling has black yolk sack still attached

[huskycow]

I received a duckling from Metzer farms on Wednesday and it had a black mass (which I'm assuming is it's yolk sack) and a pasty butt, which I promptly cleaned up. It's been 2 days, so she's now about 5 days old. She seems healthy, in that she's alert, eating, drinking, and pooping but she's smaller than the others and the yolk sack is still there, though it has shrunk (I've attached a picture for reference, she's wet because her butt was getting a little pasty again).

I just want to make sure I don't have to do anything else for her.

 

[H-B-O]

@DucksAreBest

 

[DucksAreBest]

Sorry, but I've never dealt with anything like this. Maybe @MGG or @BirdsBeesTrees know.

 

[BirdsBeesTrees]

Just leave the dried up yolk sack alone, it should fall off later.