Mallard ducklings...deformed??

[CheeseNQuackers]

Today we adopted 2 ducklings.
Having raised 2 mallard ducklings previously, we decided on the same breed. 1 of them, however...is just a tad bit different.

I've researched a little about the poof/crest/deformity...but it's all a bit confusing.
Experience, advice...anyone?

Anyway...these are my new waddle babies.
Harley and Quinn.

 

[Finny]

They are so precious! I had a mallard duck with a crest. She developed wry neck and I believe it was caused by some neurological problems that crested ducks can have. Not all cresteds develop problems though so I don't want to freak you out. I would just have some vitamin supplements in their water to keep them strong and healthy.