* Commensalism: One species benefits from the relationship, while the other is neither harmed nor helped.
* Brood Parasitism: One species (the parasite) lays its eggs in the nest of another species (the host), relying on the host to raise the parasitic young.
In the case of cowbirds and bison:
* Cowbirds benefit: They get a free ride, access to open areas created by bison, and are more likely to find host nests in grazed areas.
* Bison are not directly helped: The presence of cowbirds doesn't benefit bison.
* Cowbirds exploit the bison: While not directly harming the bison, cowbirds lay their eggs in the nests of other birds that may be nesting near bison. The host birds then raise the cowbird chicks, sometimes at the expense of their own offspring.
Therefore, the relationship between cowbirds and bison is not purely commensalistic but rather a form of brood parasitism where the cowbirds benefit at the expense of other birds, even indirectly benefiting from the presence of bison.