We have 2 sets of ducklings that were hatched only 2 days apart, but we have been brooding one set since last Thursday, and 4 arrived today. I kept everyone separated for a half hour or so, then let them in together. The 2 "older" ducks are chasing thenew ones with their mouths slightly open and pecking/bumping them. Nothing too vicious, I don't think, but is it normal? What should I watch for? We had the same scenario last year with 2 sets, but I don't remember this behavior from the older ducks.