I kept 3 drakes together in one of my chicken tractors for 4 months, they did fine, this was during the fall so they would still be actively breeding. I have had no problems with keeping drakes together, I had 2 drakes together through the entire breeding season last year and did not see any fighting but different birds will have different attitudes. Right now I have only 2 hens and 5 drakes all in the same pen, haven't seen them mate in over a month and haven't gotten an egg in a long time either. Both of the hens are in great shape, so are all the drakes I saw only a few fights when they were first introduced. I did have one more hen and 1 more drake in there but they are gone now, thanks to a racoon. You can get away with a lot of crazy gender ratios this time of the year, at least in my climate you can. Every year that I have owned mallard derived ducks I have had more drakes than hens in my flock during mid-late winter without a problem. I usually separate them out again once the drakes start to go into molt or once the hens start to lay again because that's around the time all the drakes go crazy.