PARASITIC LAYING IN RED-CRESTED POCHARD NETTA-RUFINA NESTS

Fifteen percent of Red-crested Pochard Netta rufina clutches were parasitized by Common Pochards Aythya ferina, and 22% by conspecifics. There were no differences in the characteristics of nesting sites and fates between parasitized and unparasitized nests. Nest diameter was greater in parasitized than in unparasitized nests, but no differences were found in nest depth according to nest category. Red-crested Pochard nests parasitized by conspecifics were initiated earlier than the other nest types. The clutch sizes of Red-crested Pochards were similar in nests parasitized by Common Pochards and in unparasitized nests. More Red-crested Pochard eggs were displaced outside the nest bowl in parasitized than in unparasitized nests. In addition, the proportion of incubated Red-crested Pochard eggs containing dead embryos was greater in parasitized than in unparasitized nests, probably because incubation was less efficient in parasitized nests. This was suggested by a significant relationship between nest diameter and hatching success in parasitized nests, as eggs distributed in fewer layers may receive better incubation. Females ejected more eggs from smaller than larger parasitized nests, probably to reduce the number of egg layers, thus improving the hatching success of the eggs remaining in the nest bowl.