Even though female coyotes become sexually mature around 10 months of age, Yellowstone females do not breed until they are 2 to 5 years old. An average of 5.4 pups are born per territory but an average of only 1.5 pups survive to 1 year of age. Principal causes of pup mortality are disease and starvation.

Coyotes feed primarily on voles and elk carcasses and the diet varies seasonally (Murie 1940, Crabtree and Sheldon 1999b). Ungulates provide about 45% of the coyotes’ annual biomass consumption, most of which is consumed as carrion during the five winter months.

The reintroduction of wolves in 1995 had dramatic effects on the coyote population (Crabtree and Sheldon 1999b). Wolves killed from 25% to 33% of the coyote population during each of the 1996–1997 and 1997–1998 winters, especially in the core areas used by wolves. Almost all these coyotes were killed near the carcasses of elk killed by wolves. The coyote population in the Lamar Valley dropped from 80 coyotes in 12 packs in 1995 to 36 coyotes in 9 packs in 1998 (Crabtree and Sheldon 1999b), and coyotes failed to recolonize their traditional territories in core wolf areas.

However, coyotes are flexible and adaptable animals and have already begun to travel in larger groups (Crabtree and Sheldon 1999b). Some of the surviving coyote packs are smaller and are producing larger, healthier pups with higher survival rates. Coyote packs on the fringes of wolf territories have experienced little mortality and are able to benefit from elk carcasses killed by neighboring wolves.