FACTORS AFFECTING NESTING SUCCESS OF THE CATTLE EGRET (BUBULCUS IBIS) IN LAGUNA MAR CHIQUITA, CENTRAL ARGENTINA

RICARDO TORRES; ARNALDO MANGEAUD

ORNITOLOGIA NEOTROPICAL

Neotropical Ornithological Society

Año: 2006 vol. 17 p. 63 - 71

1075-4377

The reproductive biology of the Cattle Egret (Bubulcus ibis) was studied to determine the factors affecting its productivity in Central Argentina. This study was conducted in the colonies of Laguna Mar Chiquita between 1993 and 1997. A strong effect of brood size on the number of 3-week old nestlings per nest was observed. Brood size, in turn, was influenced mainly by egg losses caused by heavy winds during storms. Death of nestlings due to starvation or sibling aggression had some effect, while other variables (predation, nest abandonment, and vegetation structure) had no effect on final productivity. Nesting success was positively correlated with accumulated rainfall during the breeding season. Rainfall stimulated faster pasture growth, which probably increased the abundance of Orthoptera, the main food item of Cattle Egrets in the study area. Nest survival was generally higher in the chick-stage than in the egg-stage, as winds caused higher losses of eggs than of nestlings. The large numbers of breeding pairs in the colonies and similar productivity to that observed at equivalent latitudes in Africa suggest that the Cattle Egret is well established in the Mar Chiquita region, an important breeding area in southern South America.