It is interesting to compare the relative size of ears to head size in the canine family. Foxes have very large ears for their head size. Coyotes have medium sized ears, while wolves have relatively small ears for their head size. The larger ear size of foxes enables them to hear and catch mice and rodents under the snow. Wolves on the other hand spend little time mousing, feeding instead on larger animals.
Coyotes fall somewhere in between the other two members of the family.
It is thought that the wolf reintroduction in Yellowstone may cause a decrease in the number of coyotes in the park. As the coyote population decreases it is expected that the fox population may increase as they will not be out-competed by coyotes which share some of the same foodbase. The prey base of wolves does not appear to overlap with the foxes prey base.