Oh no

It wouldn't be the first I've heard of a drake picking a fight he couldn't win... poor thing. I can't imagine I'll be buying any boys soon, though - no more room for ducklings, still too much of a weenie to raise meat birds haha.
Does anyone have any advice for introducing new ducklings to the brooder? The replacements from Metzer will be here this week. They'll only be a week younger, but the older girls are already noticeably bigger than they were five days ago and I'm worried they'll pick on the newbies.