Lays its eggs in other species' nests; the chicks evict the hosts' offspring. A perfect 'nature is not your friend' Wikipedia portal.
From Wikipedia
The brown-headed cowbird is a small, obligate brood parasitic icterid native to temperate and subtropical North America. It is a permanent resident in the southern parts of its range; northern birds migrate to the southern United States and Mexico in winter, returning to their summer habitat around March or April.