Have you ever watched a bird feeder and seen two birds fight over a position at the feeder or a big bird like crow or jay arrive and scare away the smaller song birds? If you have, you’re witnessing a common animal conflict over a shared resource.
Animal interactions can create two types of conflicts; intraspecies: between animals of the same species and interspecies: between animals of different species. Intraspecies competition can occur due to social status, mating or fighting over limited resources. Interspecies competition is seen typically when members of different species compete for a shared resource. These conflicts can establish something known as a dominance hierarchy, which is a complex set of rules that can govern who gets first preference.
Birds of equal size may seem to be on equal footing but there are other complex factors that contribute to who wins a conflict.
Project FeederWatch is a citizen science project where community members survey which birds visit feeders and other locations all over the world. Thanks to the project, they have documented the interspecies conflicts of over 136 North American species of birds, and there have been some interesting trends that emerged outside of the normal trend of the bigger, the better. Woodpeckers, warblers, and hummingbirds placed higher on the hierarchy than expected from their size, most likely due to their aggressive behavior or deterrents like the woodpecker’s scary bill. There were even some relationships that played out like a game of rock-paper-scissors where birds had separate one-to-one confrontations. Interspecies conflicts and hierarchies are hard to document because they change with the habitat or the season.
Here in the Eagle River valley, there are a few of these hierarchies and conflicts worth noting. Mountain goats are an introduced species that occupy the same habitat and niche as the bighorn sheep. And while they are similarly sized, researchers have observed sheep being dissuaded from approaching salt deposits by just the presence of the more aggressive mountain goats, establishing a clear hierarchy.
One of the most famous examples of intraspecies hierarchies is of course gray wolves, with numerous studies documenting the complex social interactions within and between packs. While Colorado has historically been a part of the gray wolves’ range, the only extant individuals are found near the northern border and the Colorado Parks and Wildlife has a current plan to begin reintroducing them by the end of 2023. This will surely lead to a change in coyote populations, because the interspecies competition between the two canines usually ends with the larger, more aggressive wolf on top.
Some other animals that are endemic to this area that are known to display some type of intraspecies dominance hierarchy include bobcats, mountain goats, and pronghorn antelope.
A blue jay fights a female cardinal at the feeder.
In a 2022 paper published in Frontiers of Ecology and Evolution, the authors looked specifically at interspecies conflicts and argued that they will be more common as climate change shifts and changes resource availability such as minerals, water, snow and shade. While studying these conflicts, they also found that there was a common rule across these conflicts, that the bigger animals typically won out. Competition is a healthy and necessary part of the ecosystem that can help create balance. But climate change and habitat loss can disrupt that and create a scenario where most animals will “lose.”
If you are interested in the subject of animal competitions, you should participate in the annual March Mammal Madness. It’s a simulated competition among animals with seeded divisions set in a bracket, and after each round there will be an explanation for why each animal “wins.” The matchups start on March 13 so look at the bracket soon and see if you can guess who’ll win it all!
Reese Farrow is a Naturalist for Walking Mountains Science Center and while he isn’t a fan of conflict, he recognizes that in the natural world, conflict between species is normal.