Brood parasites are a sub-category of kleptoparasite occurring among birds or insects, that lay their eggs in the nests of other species to be raised by the host. This relieves the parent parasites from the investment of rearing young or building nests, enabling them to feed only themselves, and to lay more eggs. They usually only lay one egg per nest, although in some cases, particularly the cowbirds, several females may use the same host nest.

Typically, the young of brood parasitic birds are larger than the young of the nest parent, and can out-compete them for feeding from the parent. Often, the brood parasite young will actually push the host young out of the nest to their deaths, so that the parasite young becomes the only young in the nest.

Brood parasitic birds include the old-world cuckoos, cowbirds, whydahs, and the honeyguides.

The cuckoo bees are a group of brood-parasitic insects, laying their eggs in the nest cells of other bees.

Some brood parasites are of only individual consequence for their hosts, with only minor effects on the species as whole, but the cowbirds have become a serious invasive pest in many areas due to their habitat preferences. They feed in open areas adjacent to woodlands, and will marginally penetrate the forest fringe to lay eggs in the nests of other passerine species.

As the forests in the Americas have become fragmented, this has resulted in the cowbirds becoming a significant part of a negative set of edge effects, since they have gained access to a greater percentage of songbird nests.

Brood parasites

Brutschmarotzer | Nestedo parazito | 巢寄生