Winter browsing by elk results in decline of habitat for songbirds
By Summit Voice
SUMMIT COUNTY — A steady decline in Rocky Mountain snowpack the past few decades has led to a classic cascading ecological effect, with “powerful” shifts in mountainous plant and bird communities, according to scientists with the U.S. Geological Survey and the University of Montana.
“This study illustrates that profound impacts of climate change on ecosystems arise over a time span of but two decades through unexplored feedbacks,” said 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.”
As the high-elevation snowpack dwindles, elk can stay at higher elevations during the winter and browse on plants that just a few short decades were inaccessible during the snow season, the researchers explained in their study, published Jan. 8 in the journal Nature Climate Change.
As a result, deciduous trees and associated songbirds in mountainous Arizona have declined during the last 22 years. Increased winter browsing by elk results in trickle-down ecological effects such as lowering the quality of habitat for songbirds.
The authors of the study, USGS Montana Cooperative Wildlife Research Unit scientist Thomas Martin and University of Montana scientist John Maron, mimicked the effects of more snow on limiting the ability of elk to browse on plants by excluding the animals from large, fenced areas. They compared bird and plant communities in these exclusion areas with nearby similar areas where elk had access, and found that, over the six years of the study, multi-decadal declines in plant and songbird populations were reversed in the areas where elk were prohibited from browsing.
The study demonstrates a classic ecological cascade, Martin said. 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.
“This study demonstrates that the indirect effects of climate on plant communities may be just as important as the effects of climate-change-induced mismatches between migrating birds and food abundance because plants, including trees, provide the habitat birds need to survive,” Martin said.