In some duck species, the host female does incur a cost for having her nest parasitized. The main negative effect is the displacement of her eggs from the nest when a redhead forces her way onto the nest. This reduces the number of host eggs that are incubated and hatch.
In some cases, the host may actually end up incubating more eggs from other hens than those she lays herself. A day in the life of the parasite queen is amazing because it is so different from other female ducks. The redhead prevails as one the most interesting waterfowl species in North America because of its adaptive, parasitic behavior.
Redheads aren't the only crafty ducks out there Brood parasitism is more common than you might think. In North America, wood ducks are notorious for egg dumping. Wood duck nests have been found with up to 50 eggs in them laid by parasitic wood duck hens. In most wood duck populations, up to 50 percent of the nests contain parasitic eggs.
Other North American duck species that frequently parasitize include black-bellied whistling ducks, goldeneyes, buffleheads, mergansers, and ruddy ducks-all of which are cavity nesters except for the ruddy. However, none of these species exhibits the dual strategy demonstrated by redheads.
When parasitism is the only option
The black-headed duck of South America is the only waterfowl species that is an obligate parasite: Black-headed duck females must lay their eggs in other nests, as they never build their own nests or incubate their own eggs; instead, they leave all maternal duties to unsuspecting hosts.
Favorite hosts include coots and rosy-billed pochards, but black-headed ducks' eggs have also been found in nests of raptors and predatory birds.