Chick adoption and subsequent survival in Greater Rheas.

LABAQUE, MC.,; NAVARRO, J.L.; MARTELLA, M.B.

Oudtshoorn (Sudáfrica)

Congreso; Second International Scientific Congress (Ratites in a competitive world).; 1998

The Greater Rhea (Rhea americana) is one of the two ratite species of South America. The male assumes nest building, all incubation, and leads the chicks after hatching, protecting them during several months. Under an appropriate manipulation, farming operations could take advantage of this behavior to improve chick survival in an effortlessly 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 survivorship of  adopted vs. male’s own chicks in semi-captive populations. During November to December 1996, groups of marked chicks (1-11) of Greater Rhea hatched in incubators were released at various day intervals, in the presence of males with own broods, in a experimental area (30 ha) near Córdoba (Argentina). In 100% of the cases (n = 12) males allowed the released chicks to mix with their own chicks. However, this process took more time as each male’s own brood increased, independently of the time of the breeding season (r= 0.66; P < 0.05). The stage of the breeding season (before or after of the median hatching date) did not affect the survival of adopted chicks (Mann Whitney, Z = 0.70; P = 0.49). Overall chick survival in June 1997 was 23% of the number hatched. This value is much lower than the one for wild populations of Greater Rheas (50%-60%) and for the Lesser Rhea (Pterocnemia pennata) in commercial farms (65% at an age of four months). Main causes of this comparatively high rate of chick deaths were predation, drowning in water and the adverse effect of severe rains that led to hypothermia. In conclusion, an efficient manipulation of the adoption behavior exhibited by males of Greater Rhea could help in decreasing costs and labor at farms.