Climate change: what’s good for elk is bad for birds

When elk are excluded, aspen growth dramatically increases (Coconino National Forest, Arizona, May 2011) Photo: Tom Martin, USGS

A just-published U.S. Geological Survey (USGS) and University of Montana study demonstrates how the declining snowpack in the Arizona mountains over a 22-year span has affected songbirds, producing a “classic ecological cascade” according to Thomas Martin, USGS Montana Cooperative Wildlife Research Unit.

For example, he said, from an elk’s perspective, less snow means an increased ability to freely browse on woody plants in winter in areas where they would not be inclined to forage in previous times due to high snowpack. Increased overwinter browsing led to a decline in deciduous trees, which reduced the number of birds that chose the habitat and increased predation on nests of those birds that did choose the habitat.

As a test, for six years they fenced large tracts of land to keep elk from grazing there and found significant recovery of the plant and bird populations compared to unfenced areas.

“This study illustrates that profound impacts of climate change on ecosystems arise over a time span of but two decades through unexplored feedbacks,” explained USGS director Marcia McNutt. “The significance lies in the fact that humans and our economy are at the end of the same chain of cascading consequences.”