Similar Polygamous Mating Patterns Have Been Found in Both Birds

Similar polygamous mating patterns have been found in both birds and humans.Under what circumstances would several female birds mate with the same male bird while other male birds are left mateless?

A) when one male bird has a particularly resource-rich territory
B) when one male bird is particularly physically attractive
C) when there is an overabundance of female birds
D) when there are very few male birds to choose from