I know nothing about pheasants, Blissfully, but the Muscovy ducks on our lake often form trios of two males and one female or two females and one male. Sometimes there are four of any sort of combination. When ducklings are hatched, the family group, as I call it, serves as security guards for the little ones. As the ducklings get old enough to swim about the lake, the older ducks are the wingmen or wingwomen, as the case may be.

It's my guess that the "extra" ducks are young adults that haven't found a mate yet or older ducks that lost a mate.

Maybe the same is true of pheasants??