A note on chick adoption: a complementary strategy for rearing rheas

The Greater Rhea ( Rhea americana) is one of the two ratite species of South America. Its breeding system combines polygyny and sequential polyandry, in which a group of females lay eggs in more than one nest. The male builds the nest, incubates, and protects the chicks for several months. Males frequently accept chicks from other groups, including them in their own brood. Farming operations could take advantage of this behaviour to breed chicks in an effortless way. However, the extent to which adoption and care of adopted chicks occurs is not well known. Here we present data on adoption of chicks by males and the comparative survival of adopted vs. male's own chicks in a semi-captive population. Groups of marked chicks (one to 11 individuals) of Greater Rhea hatched in incubators were released at intervals near males with their own broods. The inclusion of the released chicks was checked and the survival of both groups within each brood was monitored. In 100% of the cases ( n=12) males allowed all the released chicks to mix with their own chicks. However, this process took more time as the size of each male's own brood increased. Survival of the two categories of chicks was not significantly different. However, a slight trend towards higher mortality of adopted chicks was observed when they were mixed with broods of substantially older chicks. The stage of the breeding season did not affect the survival of adopted chicks. The mortality rate of whole broods (adopted+own chicks) was not significantly different between broods larger and smaller than the median. However, the benefit/cost ratio of this approach and appropriate complementary management actions to decrease the comparatively high mortality rate of the chicks need to be studied in more detail.