My first guess would be that it is boys picking on and attempting to mate with the girl. It seems like they are being particularly aggressive, in my opinion, which is most likely to happen if there is a shortage of females. But if there isn't a girl around, the boys will do that to each other. My guess is you have at least one girl and two or three boys. I couldn't see from your photo that there were any sex feathers. Which one has them?
Drakes will develop their sex feathers on their own time frame, so you won't necessarily see all the sex feathers at once, even if they are all the same age.
Once egg-laying commences, and mating occurs regularly, I think you'll have a better idea.
If you do have 2-3 drakes and only 1 or 2 females, you will either need to get rid of all the drakes but one, or separate the sexes. Once the ducks start laying, the drakes can get really aggressive with them, if they are competing over one duck -- they can hurt and possibly damage her internal organs.
Drakes will develop their sex feathers on their own time frame, so you won't necessarily see all the sex feathers at once, even if they are all the same age.
Once egg-laying commences, and mating occurs regularly, I think you'll have a better idea.
If you do have 2-3 drakes and only 1 or 2 females, you will either need to get rid of all the drakes but one, or separate the sexes. Once the ducks start laying, the drakes can get really aggressive with them, if they are competing over one duck -- they can hurt and possibly damage her internal organs.
