[quack!]

A couple of weeks ago I noticed a pair of Wood Ducks here have a brood of young ones (was 9 to begin with, now down to 8). I thought it a bit odd because I've never seen them with ducklings at this time of year. I did a bit of a google and according to BiB, the breeding season is reportedly September to November in my part of the world. I know a lot of birds can raise more than one brood a year if conditions are favourable, but I'm wondering if what I'm observing is a little unusual, or very unusual?

Also, I was checking them out just now (that's when I noticed the absence of one baby) and the male put his head down and hissed at me as they do. I didn't approach any closer, just stood and watched. They crossed over the little roadway next to my place to another grassy area where there were another pair of adult birds. The father put his head down, extended neck and chased of after them. He spent a good twenty or thirty seconds driving the other birds off. my question is why would he bother doing that, what threat would those other two Woodies pose?