Buffalo Birds and Bison – A Yellowstone Sighting

July 10, 2023

A bison walks across grassland in Yellowstone National Park.

While ‘oohing and ahhing’ over the largest land mammal in North America, did you ever notice the small, seemingly ever-present bird perched atop a bison’s back or following closely around its feet? Enter… the “Buffalo Bird” (aka brown-headed cowbird).

a herd of cattle standing on top of a grass covered field — Courtest National Park Service

a bird standing on top of a grass covered field — Courtesy Neal Herbert/NPS

A female brown-headed cowbird seeks insects in the grass and a male rides atop a bison's back. — Courtesy Neal Herbert/NPS

While other birds are priming nests for their young—laying eggs and gathering insects to bring back to their very hungry chicks—this bird is filling its belly for itself. That’s because the cowbird doesn’t have a nest to go home to.

Brown-headed cowbirds eat the insects the bison flush up from the grasses and travel along with the herds, sometimes covering grounds of 10 to 20 miles in a single day. Without a stable food source to depend on in close proximity to home, females lay their eggs in existing nests made with care by other bird species. With luck, these strangers will incubate their eggs and raise the cowbird’s young (often at the expense of their own offspring), a behavior that earns them a title of “brood parasite”.

A young Buffalo Bird doesn’t know what its own kind looks like or what it should sound like because it never heard the song of its parents as they fed it in the nest or taught it to fly. Instead, experts believe the young cowbirds are tuned to respond to the “chatter” of adult cowbirds and will be attracted to its source, from there learning to behave as an adult. This paired with nighttime excursions away from the nest (a topic still being studied) might prevent the young bird from imprinting, and thus mimicking, its foster parents.

A male cowbird courts a female cowbird in a tree.

When it comes to courtship the buffalo bird has a song and will approach a female to sing it to her. While singing the male bows and fluffs his feathers and the two will mate if she accepts. His dark feathers and muddy head are a contrast to her dull, grayish coloration, a trait that may make it easier for her to sneak into other bird species’ nests.

In Yellowstone, the brown-headed cowbird truly is a Buffalo Bird, traveling with the thousands of bison roaming across the landscape. This commensalism, a relationship where the birds benefit without harming or helping the bison, has stood the test of time and is a testament to what the Great Plains and American West may have looked like when free-roaming bison outnumbered cattle. Consider booking a July tour with us and look for these birds as we enter the mating season for the bison!

To learn more about Laura and the rest of the Yellowstone Wild team visit our “About Us” webpage.

Text courtesy Yellowstone Wild Guide Laura L. Photos courtesy Yellowstone Wild Guide Isaac Rath (top), National Park Service, William Link/USGS (bottom).