Optimal clutch size in nycticorax nycticorax and egretta garzetta

Abstract

The breeding success of night heron and little egret showed few and non-systematic variations between two heronries over four years. The most frequent clutch sizes were 3. and 4 eggs, respectively. However, the highest productivity was attained by larger clutches: night heron nests with 4 hatched chicks and 2.6 survivors; little egret nests with 6 chicks and 4.6 survivors. These results confirm a pattern observed in other birds, namely that modal clutch size is lower than the most productive clutch size. Our results are consistent with the hypotheses that the discrepancies between actual and optimal clutch size is due either to a local abundance of food, or to the existence of individual optima. © 1993 Taylor & Francis Group, LLC.