Bald Spot and Swollen Neck on Ducklings, help

[Russell2000]

So my three ducklings that were born two or so weeks ago have been doing very well but today I noticed something very odd during their bath/swim time. All three appear to have bald spots around the necks and they also seem very "swollen" I guess... Pics below... All three are similiar, I have read that it could be a full crop or possibly a ruptured air sac? The thing I dont understand os how all three of them are the same. I appreciate the help.

 

[ChickenCanoe]

That is the crop. It is full of food. No problem.

 

[Russell2000]

Thanks, wasn't sure

 

[Russell2000]

Thanks, wasn't sure

 

[DuckyDonna]

@Isaac 0 @Miss Lydia this doesn't look like a crop to me!

 

[Isaac 0]

Looks like a crop to me, I notice this was posted in the evening so it would have been full, I would only be concerned if it's still full as of this morning.

 

[ChickenCanoe]

It is exactly where the crop is located and it swells when eating. That swelling makes the feathers look more sparse in that area. It is also much more noticeable in very young birds.
If it looks like a duck, quacks like a duck, and walks like a duck - it's a duck.