After the Bison Peak pack sings, other coyotes join in a group yip-howl. The Druid pack takes up the melody, then the Jasper pack, then the Amethyst pack, the song working its way down the Lamar Valley, echoing off the hillsides. This is an unprecedented time to observe coyote behavior in Yellowstone. For the first six years of the study, coyotes had few natural predators in the Lamar Valley. Then, in 1995, the federal government reintroduced gray wolves to the park.
Wolves kill a lot of coyotes, primarily loner adults but also incautious pack members.
Crabtree and Sheldon have been documenting the social, behavioral, and dietary changes among coyotes since the reintroduction. Their findings have helped explain how the coyote population, in the face of unrelenting persecution, has proven so extraordinarily resilient. During the past four years the Yellowstone wolves have reduced the coyote population by about 30 percent. The coyotes have had to rearrange their territorial boundaries, alter their hunting habits, and cope with the continual disruption of their pack structures. Still, the animals are not going to be wiped out in the area.