A Fence That Keeps Out Elk and Moose but Lets Smaller Animals Through

The question

Heavy browsing by large hoofed animals, and the Lawn Lake flood, degraded areas of Rocky Mountain National Park that once held plenty of willow, with knock-on effects for the ecosystem. Fencing lets such areas regrow on their own, and woven wire can keep out everything but the smallest mammals. The park wanted something more selective: a fence that stops elk and moose but lets smaller animals such as coyotes, deer, cougars, foxes and badgers through, keeping the ecosystem more natural while limiting browsing on aspen and willow.

The test

Edward Gage and David Cooper of Colorado State University evaluated a trial fence around Fan Lake. Its woven wire mesh reached 76 inches high, but its lower edge was raised 16 inches off the ground. The idea: adult elk and moose would neither jump over the top nor crawl under, while deer and smaller animals could pass beneath.

They checked in two ways:

• track plots, 2 meters by 3 meters, at eight spots inside and outside the fence, swept clean and checked periodically for prints;
• two motion-triggered cameras aimed along the fence line.

The results

The design worked. Elk tracks were plentiful outside the fence, and only once did an elk get in during the study, perhaps by jumping from a snowbank. There was no sign of moose inside. Both the tracks and the cameras showed smaller mammals readily passing underneath.

After the project, under the park's Elk and Vegetation Management Plan, the park built similar fences to protect chosen stands of aspen and willow from browsing, in the hope that they will soon recover.

This summary rests on reports available when it was written and is not a statement of park policy or a definitive account of the research. More on the park's research: nps.gov/romo.

Sources

• Bert Cushing, "Elk and Moose Exclusion Fence," National Park Service, Rocky Mountain National Park. https://www.nps.gov/articles/elk-and-moose-exclusion-fence.htm
• A photograph by the researchers is not reproduced here.