Canít Find a Moose? Wait 300 Years
by Dr. Nathan Varley
June 11, 2010
A recent survey of park visitors indicated the wildlife species people most want to see is a moose. Ok, actually among the herbivores, moose were an overall 3rd place finisher behind the big carnivores, grizzlies and gray wolves. While guiding for The Wild Side, I often get the request of finding my guests a moose, and this invariably comes after we have spent all morning securing sightings of the first two species on the list. From that point on, it’s a serious up-hill climb.
There are at least two reasons that make finding a moose, the largest and most widespread species of the deer family, a difficult request in northern Yellowstone. First, it is usually already late in the day for finding a moose--an active moose is a rare occurrence when temperatures are warm. Being a temperate species distributed in forests throughout the northern hemisphere, moose populations dwindle in number in the southern extent of their range. It's odd to think of Utah and Colorado as being marginally too warm for moose, but the bottom-line is moose are not good at thermo-regulation (they don't cool off well). So, if there is any warmth at all to the day, they are lying in the shade. If it is generally too warm in the region, they won't live there.
The second reason, and more deeply fascinating reason, lies in the realm of ecology and population dynamics. Currently, there just aren't that many moose in northern Yellowstone.
To understand this dynamic better, I recently attended the field seminar, Moose Ecology, at the Yellowstone Association Institute taught by Dr. Dan Tyers. Dr. Tyers, a US Forest Service biologist, is a well-known expert on moose in our region owing to his extensive studies over the past 30 years, many of which were published in his PhD dissertation at Montana State University.
Dr. Tyers made the point: moose populations in the greater Yellowstone area are anomalous among North American populations due to how they are able to respond to the primary disturbance force in their forest homes, wildfire. After the 1988 wildfires that burned over one third of the park's forested areas (and much beyond the park), moose had lost much of their critical winter range.
While the diet of the moose here varies widely in the summer including many shrubs, forbs, and aquatic plants, the staple of their winter diet is subalpine fir, a common conifer species in the understory of old growth forests. These were the primary forests that disappeared after 1988. These old forests, once in great abundance after many decades of fire suppression, provide the food and cover for moose to over-winter. In many places throughout the world where moose are found, burns and other forest disturbances (e.g., timber harvest) create habitat for moose. The early stages of re-growth include a lot of shrubs that moose eat. But in the Yellowstone area, these shrubs are largely absent from the post-burn flora. Only conifer samplings, mostly lodgepole pine, grow from the poor, thin soils found throughout much of the region and moose foods are largely absent.
How great has the fire effect been on northern Yellowstone's moose? Nobody can say for certain because moose are notoriously difficult to census, but my own eyeball estimate of Dr. Tyer's rough figure of the post-1988 population decline was 90%. Dr. Tyers also mentioned that moose were relatively recent arrivals to this region colonizing after the receding Pleistocene glaciers. There may not have been moose in the greater Yellowstone before 1800. The population increased rapidly and peaked around 1945. A slow decline preceded the more precipitous decline following 1988.
I often hear that the observed decline in moose numbers locally is due to the return of the predators, those first two species on the must-see list, grizzlies and wolves. Certainly these carnivores do prey on moose when available. Grizzlies are known to show up in abundance near the towns of Cooke City and Silver Gate at the same time as the local moose are giving birth to their calves. But few adults are taken by these predators that tend to favor the more abundant elk and deer. Rather, the far greater influence on the number of moose we see has been the change in habitat as imposed by wildfire. Even without the predators, moose will never again become abundant without the right habitat.
So, how long until their winter homes grow back? Unfortunately for us moose lovers, these changes occur slowly. Dr. Tyers offered one estimate of about 300 years as the time it takes for the lodgepole pioneers to mature and the spruce and subalpine fir to become abundant in the shady understory. So if one wishes to see a moose, and doesn't have 300 years to wait around, one has to be lucky.
Learning about moose in northern Yellowstone from Dr. Tyers was similar to many of my investigations of Yellowstone ecology. It's more complicated than it first appears. I find nature's cycles quite fascinating and comforting even when experiencing the low in a particular cycle, moose numbers in this case. Our field trips, while enjoyable in the amount of moose habitat, food, and pellets we found, were largely devoid of sightings, with one notable exception. Returning from our field trip to the Lamar Valley Buffalo Ranch, our class spotted two moose, a cow and yearling calf, bedded among the willow stands near the river. I have seen very few moose in this area in over the years, but I have been told by those who remember back to the 1970's that at that time they used to be commonplace in this area. I took these two to be an early indicator of a slow return--very slow, but that is already underway.