As we mentioned in last week’s column, we had the amazing opportunity a few weeks ago to tour through one of America’s most famous natural areas, Yellowstone National Park. The popularity and accessibility of Yellowstone to human visitors and the success in conserving and growing populations of some of the large mammals that are gone from most of their North American range means that humans and these large animals come into close contact. We saw it firsthand throughout the park but it was particularly memorable when we stopped at the site known as Mud Volcano.

The parking lot was full of cars and families heading up the boardwalk. Just then a small herd of huge, brown, wooly bison decided they wanted to get to a spot on the other side of the parking lot. They descended from a small hill, ambled past the signs and boardwalk, and, in single file began slowly but purposefully walking through the center of the lot. Rangers began shouting to people to stay away from the bison and get into their cars. Moms and dads tried not to sound alarmed as they told their kids to get back into the hot car they had just escaped from after a long ride. As usual, a few people ignored the rangers and moved closer to try to get close-up photos or video. A little later as we were viewing the bubbling hot spring another bison decided to use the boardwalk for a shortcut to a small pasture (after Dad had told Evan that the bison wouldn’t walk on the boardwalks!).

This experience certainly showed fairly dramatically how different species interact with each other in this big natural world of ours. It got us thinking more about how different species of birds can interact with each other, too.

The most obvious interaction is probably between predator and prey as in the Cooper’s hawk, sharp-shinned hawk,  or merlin that survive by making quick, sneak attacks on small songbirds, including sometimes those attracted to our backyard feeders. American crows, blue jays, and various species of gulls are also more than ready to be predators of other bird species, though they are more likely to take eggs or nestlings since they don’t have the speed or skills to easily take adults.

More intriguing, perhaps, is the idea of competition between species. It’s not uncommon to see a herring gull that has found a choice food item being chased by a larger great black-backed gull or even a bald eagle that tries to force the bird with the food item to drop it or cough it up. We have even seen common ravens chasing herring gulls at landfills until the pursued gull dropped its food item.

Some bird species can compete for nest sites, especially in species in which good nesting locations are in shorter supply. On Maine’s outer islands, gulls often take over islands or parts of islands for nesting that would otherwise be occupied by common and roseate terns. House wrens and house sparrows will sometimes even destroy the nests, eggs, or young of other cavity nesters in their territories, apparently to try to make the nesting sites available for their own use. Even “mild-mannered” tree swallows and eastern bluebirds are known to fight over nest boxes or nest cavities ... but we humans nonetheless enjoy having them as neighbors!