Interspecific nest parasitism by redheads on islands in southeastern Alberta

Abstract

I studied interspecific nest parasitism by redheads (Aythya americana) from 1976 to 1978 in a population of upland nesting ducks on artificial islands in southeastern Alberta. Of 685 duck nests, 19% were parasitized by redheads with a mean of 2.68 parasitic eggs per host nest. The proportion of nests parasitized increased with the density of host nests on the islands. There is also some evidence that the rate of parasitism was influenced by the nesting density of redheads. Mallards (Anas platyrhynchos) had the greatest percentage of nests parasitized by redheads whereas lesser scaup (Aythya affinis) had the largest number of parasitic eggs per nest. Redhead parasitism affected reproductive output of hosts by increasing nest desertion. Finally, the parasitic activity of redheads was reduced during a season characterized by drought conditions.