Spring in the Northern Rockies isn’t all flowers and butterflies

Jess Edberg  – International Wolf Center

Spring is a time of rebirth, regrowth and rejuvenation for most. However, for some species in Yellowstone National Park it is a time of death. A recent study of how gray wolves influence the amount of carrion available to scavengers adapting to climate change provides a different view of this season of change.

In Yellowstone National Park (YNP), winters are getting shorter. This climate change is measured by the number of days snow is on the ground. A shorter spring (time-span between late winter and summer) is a result of an increased number of days with temperatures above freezing and a decrease in snowfall. What does this have to do with gray wolves you ask? According to a study conducted by Christopher C. Wilmers and Wayne M. Getz of University of California, Berkeley, gray wolves have a significant effect on how much carrion is available for scavenging species in YNP.

The authors generated models to estimate the effects of shorter winters on scavengers. In a scenario with reduced snow cover and an absence of gray wolves in YNP, there was a reduction of carrion available to scavengers of 27 percent in March and 66 percent in April. However, in a scenario with wolves present, that carrion reduction was only 4 percent in March and 11 percent in April. What does this mean?

According to the study, when there is less snow on the ground, elk (and other ungulates) are better able to forage for food. They also expend less energy both in foraging and traveling. Their quality and quantity of food is increased and the “physiologically stressful winter period is shortened (Wilmers & Getz). With this boost in food and energy, late-winter elk mortality declines thus reducing the available carrion.

Gray wolves play a role in this scenario through their hunting. When they are successful in their hunt, whatever they do not consume is available for scavengers to feast upon. Thus, producing additional carrion.

By allowing this food chain to cycle, gray wolves will help buffer the reduction in carrion, extending the time for scavenger species to adapt to the changing ecosystem they live in.