Reproductive success of wild Lesser Rheas (Pterocnemia -Rhea- pennata pennata)in northwestern Patagonia, Argentina

BARRI F.R.; MARTELLA, M. B; NAVARRO, J.L:

Journal of Ornithology

Springer

Año: 2009 vol. 150 p. 127 - 132

1439-0361

We studied the reproductive success of a wildLesser Rhea population (Pterocnemia -Rhea- pennatapennata) during two reproductive seasons (2004/2005 and2005/2006) in north-western Patagonia, Argentina. Theparameters recorded included population and nest density,clutch size, hatching success, chick survival (up to 3months of age) and percentage of chicks that reached thejuvenile stage after the winter. We also estimated thepercentage of males that attempted to nest and of those thatwere successful (those producing at least one chick), dailynest mortality rates (DNMR) at different stages of thenesting cycle and the probability that an egg that has beenrecently laid will produce a chick. On average, both yearspooled, the density of this population of Lesser Rheaswas 1.55 ± 0.2 individuals/km2 (SE), nest density was0.17 ± 0.04 per km2, clutch size was 20.8 ± 6.4 eggs,hatching success was 74.4% ± 11.3, Mayfield’s probabilityof an egg that will produce a chick was 0.64, chicksurvival was 65.4% ± 14.5 and percentage of chicks thatreached the juvenile stage was 26.3%. Nearly a quarter ofLesser Rhea males in the population attempted to nestduring a breeding season, and the DNMR was significantlyhigher during the laying stage (most nest failures were dueto anthropogenic disturbances related to livestock raisingactivities). Nesting success, hatching success, and chicksurvival of Lesser Rheas were higher than those of theirmost closely related species, the Greater Rhea (Rheaamericana), whereas the percentage of chicks that reachedthe juvenile stage was similar due to high winter mortalitiesof chicks. We suggest that the increase in reproductiveeffort is a strategy of this species to overcome environmentalconstraints.