Migration season is coming for deer and elk

Migrating Elk     Photo by Josh Metten
Migrating Elk Photo by Josh Metten

By Terry Thomas     Post Register, November 7, 2019


Many years ago, when I was radio-tracking mule deer in eastern Idaho  as part of my university studies, an early October storm, similar to the  one we have just experienced, dumped about a foot of snow on the summer  ranges. Over the next week, all of the marked deer vacated the higher  elevations and started on their migratory paths. Thick, muddy trails cut  through the snow indicated that the radio-collared deer were not the  only ones to move. Within short order, the mountains were empty of mule  deer and the lower country seemed like a hunter’s paradise.

Once  the storm moderated, though, most of the marked deer stopped migration,  waiting instead for the weather to encourage them to move on to winter  range. This way they could continue to take advantage of forage that  would soon be unavailable, saving winter range forage for the tough  times ahead.

What has been fascinating to witness over the years as more animals  have been marked, is that the animals have definite migration corridors.  A corridor is a reasonably wide swath as opposed to a trail or a path  that might conjure up visions of a single track. It is often a ridgeline  or a canyon or some other geologic feature or combination thereof.  Within a corridor, animals may wander to take advantage of new resources  or avoid obstacles and developments. A corridor may be several miles  wide. Interestingly, within the corridor, individual deer often used  exact places, say a grove of aspens, year after year, demonstrating a  high fidelity to their own route. Corridors were often used during both  spring and fall migrations.

Elk do the same thing. When winter  weather (research shows that it takes about 17 inches of snow) forces  them to move off summer ranges, they have a definite location or winter  range that they are headed to and they have a specific way to get to it.

A question arises: What happens when a single storm drops several  feet or more? Can animals become trapped? Certainly, a major snow dump  can prevent them from crossing a major pass on their corridor. For  instance, a doe mule deer radiomarked at Sand Creek was found summering  on the west side of Jackson Lake in Grand Teton National Park. It is  certainly conceivable that an early storm could force her to find winter  range elsewhere. She might hook up with other deer that make the long  journey to Wyoming’s Red Desert or perhaps she will find her way to the  feed ground at the National Elk Refuge north of Jackson.

Bucks  tend to be less traditional than does. They may change winter or summer  ranges, especially when they are younger. They are less likely to hang  with momma and more likely to seek the company of other males, following  them to new home ranges.

One thing is sure. The more  radio-tracking collars are placed on more animals, the better biologists  understand animal movements. There are usually plenty of surprises when  animals move in unexpected directions. For example, the mule deer  wintering at Tex Creek east of Idaho Falls typically head south and east  in the springtime. However, research that repeated my own work with  more and better equipment found that a small contingent actually goes  northeast, crossing the Snake River near Clark Hill. Without the  collars, this movement would have never been detected and management  could suffer for it.

 Terry Thomas is a wildlife biologist and naturalist. You can read more of his work on his website, www.nature-track.com, or pick  up a copy of, “The Best of Nature,” a collection of more than 100 of  Thomas’s best nature essays at the Post Register. Follow him on  Facebook, Nature-track. 

Terry Thomas
Terry Thomas