Brown-headed Cowbird on a Bison

Birds like Brown-headed Cowbirds and Magpies will remove and eat ticks and other parasites from the large animals' (such as elk and Bison), skin and fur. It's a symbiotic relationship: the bird gets a meal, and the mammal gets rid of some parasites. It is theorized that the Cowbirds evolved into laying their eggs in the nests of other birds so that they could follow the roaming bison herds, one of their main sources of food.

Done