I dont think it's a hormonal thing as opposed to muscovies tend to be particular to being around there own kind also for future reference muscovy ducks are beautiful but have a wild side and they are substantially different then pekins from the start
In my experience muscovies tend to be pretty scrappy birds! Id suggest getting your other breed of duck a few friends and having a muscovy flock and then your other flock
I've had too many drakes vs hens it was challenging to say the least roos and hens not quite as bad as long as the grumpy bird goes should settle down when hes acclimated and learns the ropes!
Also FYI: all chickens have buds on their legs from which spurs can grow. In most hens they remain latent but they can grow on occasion so that is no indicatation of this "sex change"
I think any predator aside from maybe a rat would need to be very creative to get in those openings. Good for ventalation though I would personally leave it be
Sometimes chickens are hard to follow !! I've tried to see where my wanders ago , never made it to where they were going depending on where you live , it's winter and my chickens sure arent laying and definitely have no nests:hit