Anomalies in the eggs of diving ducks of the genus Aythya

Anomalies were observed among the eggs of three species of diving ducks, including a shell-less egg outside the nest of a canvasback (Aythya valisineria) and dwarf or runt eggs in the nests of lesser and greater scaups (Aythya affinis and A. marila). Shell-less eggs are rarely documented in wild birds. Runt eggs are more frequently documented, but no published record of occurrence was found for scaups. Observations indicate a frequency of occurrence of runt eggs in scaups of 0.10%, similar to that reported for a number of other species.