Cayuga ducks gender?

[Breill]

We have 2 Cayuga ducks nearly 16 weeks, both believed to have been female due to lack of drake feather and both quack but we have recently seen them mating in the pool, but seeing as both seem to be female were now rather confused

 

[Isaac 0]

If they QUACK, they are females. When there is an absence of a male in their life they will sometimes try to mate with each other.