Is there a difference in reproductive performance between cooperative and non-cooperative species? A southern African comparison

Abstract

For cooperative breeding to be a strategy under positive selection, individuals should accrue some benefit, or at least not suffer a loss, compared to alternative breeding strategies. Cooperative breeding is often associated with habitat saturation (where the opportunities for pairs to establish new territories are limited), and such species are, thus, assumed to have lower per capita reproductive success than their non-cooperative counterparts. To test whether different breeding strategies affect reproductive success and progression through each breeding stage, we compared cooperative versus non-cooperative breeding strategies across a range of small to medium-sized birds in semi-arid open and grassland habitats in southern Africa. We found that in general, cooperative breeders fledged their young significantly earlier and raised more broods per season than non-cooperative species of similar body mass. Within phylogenetic families, we found cooperative species had shorter nestling periods, and that the duration of the nestling period tended to decline as cooperative group size increased. We then examined in detail two species sharing the same habitat and similar foraging niches, but with different breeding strategies: a cooperative breeder and a biparental breeder. In each species, we followed the fate of breeding attempts from incubation until nutritional independence of young. We found that the cooperative breeder fledged young earlier and invested in overlapping broods more often, resulting in lower nest predation and multiple clutches successfully raised to independence per season. This resulted in more offspring surviving per adult. These results suggest that, due to changes in breeding behavior as a consequence of helper presence (earlier fledging, overlapping broods), cooperative breeding could provide equivalent reproductive success to non-cooperative breeding strategies.