White-Fronted Bee Eaters Are Birds That Mature at About One

White-fronted bee eaters are birds that mature at about one year of age but often stay with their parents to help raise the next brood of siblings even though they could be raising their own offspring. Why would they do this?

A) The parents can't successfully raise a nest of offspring without help.
B) The young birds need a year of practice before they can successfully raise their own offspring.
C) There aren't enough mates to go around every year and only more mature birds can attract mates.
D) There aren't enough nesting sites for everyone every year, and more mature birds are better at defending territory.
E) There is no explanation for this.