Yellowstone Moose Numbers Dropping
Prior to that afternoon they had gotten along. They had an agreement. The dog ignored him; he ignored the dog. Suddenly the rules changed. Alerted by the surprised gasp coming from some guests to our Western Montana Lodge, I turned just in time to see him doing his best to pummel my dog, Pete, into the ground.
It was probably earlier guests from Georgia who precipitated the change. Intrigued by his size, the Georgia visitors had frustrated and angered him in their attempt to get some ‘close up and personal’ photos. Obviously, he didn’t like such attention.
Our winter visitor was just one of the many Shiras Moose who call Montana’s Centennial Valley home. Moose numbers appear to be on the rise in the Centennial and around Island Park, Idaho [http://www.islandparkchamber.org]. However, such is not the case in many other areas. Yellowstone National Park, Grand Teton National Park, the greater Jackson area, sections of Canada, and several areas in Alaska are experiencing declines – some quite sharp.
Moose were first documented in Yellowstone National Park in the early 1880’s. Hard to count, due to their illusive and solitary nature, reliable moose numbers can be quite difficult to verify with certainty. Although specifics are hard to pin down, scientists suspect the numbers, which rose significantly after 1900, began to decline several years later. Low counts in 1985 confirmed this theory. By the late 1980’s surveys suggested a total Yellowstone National Park population of fewer than 1000 moose.
While numbers have remained stable across most of Wyoming, counts in Jackson have also shown a sharp decline. Moose numbers dropped to 1,700 two years ago, down from a high of 3,500 in 1992. Similarly decreasing numbers appear in many other areas across North America.
Why are the numbers increasing in a few areas, while they decline in many others? In an attempt to answer this question, a handful of researchers and scientists have latched on to several theories. These include: wild fire (primarily in Yellowstone National Park), predation, relocation, hunting, lack of feed, or a combination of several issues (and probably some yet unknown).
The recent fire in Yellowstone National Park certainly had an impact on many species, including the moose. Many scientists expected Yellowstone’s fire to increase moose habitat. However, this has not been the case. After a catastrophic fire the heavy canopy of a mature forest is depleted. Deciduous plants, including willows and aspens, which are often crowded out by a mature forest, usually prosper in the now abundant sunlight. However, in Yellowstone, this has not been the case. Partly due to elevation, partly due to a combination of other factors, the deciduous growth which was expected has not occurred.
Therefore, instead of increasing moose habitat, the fire in Yellowstone National Park has greatly depleted their food supply — particularly in winter. In a normal situation, moose browse, primarily on willows during the summer and a combination of willows and subalpine fir during the winter. Of course, snow depths effect where and when they feed. While the snow is relatively shallow, moose frequent the willow stands on valley floors and along stream and lake shores. As the snow deepens, they move further up the mountain side, seeking the heavy tree canopies.
Thick tree canopies prevent heavy snow build up as well as deterring the crust which forms on the top of snow exposed to sunlight. These conditions allow them to move under the forest canopy with greater freedom. In addition, the heavy cover in a mature forest provides the shade and moisture required in the summer by the subalphine fir – a major component of their winter diet. However, with the loss of so many acres of mature forest in Yellowstone, they have lost a majority of their winter food source.
The fire’s damage is something from which recovery will take many, many years. Although the fire provides obvious benefits, and although it is a natural force of nature which Yellowstone has experience before, the results of fire are long lasting. A catastrophic fire tends to sterilize the landscape. Often the only tree seeds which remain behind are those of the lodgepole pine – sometimes called the weed tree of the evergreen forest. Although after the fire the moose, in desperation, browsed on some lodgepole, this is not their normal food. Perhaps in 200 – 300 years we will again see a return of the subalphine fir, and thus good moose habitat in Yellowstone National Park. Nonetheless, the winter food situation, at least in areas most heavily burned, looks bleak for the foreseeable future.
However, not all areas which are experiencing declining numbers have experienced a recent catastrophic fire. Yet, one thing common to most areas is a healthy predator population. Grizzly bears are the primary moose predator, but wolves can also bring down a full-grown moose. And, perhaps more important, wolves are known to prey on calves. Although many adults in areas experiencing decline have been collared in an attempt to determine what is causing their decreasing numbers, moose calves have not been collared. Therefore, it is difficult to determine how many calves are born versus how many calves reach adulthood.
Solitary creatures, moose are hard to monitor, in the best of circumstances. A semi-accurate count of the young is even harder to obtain. Thus, the full predation impact on the declining numbers is hard to determine. One thing is certain. It is having an impact.
Different areas are handling the situation in different ways. In Yellowstone National Park and Grand Teton National Park, the wolf and Grizzly remain protected by the Endangered Species Act. In other areas, wolf and sometimes even Grizzly management is handled quite differently. For example, in one area of Alaska, wolves have been shot to help control their impact on the moose and Caribou populations. Although not a pretty picture, the wolf, having no natural predator, has the potential of becoming a lethal weapon if not controlled. This is considered by some, one way to control them.
Another theory related to the declining moose numbers is starvation. In Grand Teton and Yellowstone, at least, scientists are suggesting the moose may have outgrown their food source. Moose are hard on willows. In many areas the willows, which provide a necessary habitat for many species of songbirds, have taken a beating due to moose and elk browsing habits. However, studies have also shown other factors at play in the willow decline.
In some places exclosures have been built to protect willow stands from browsing. These exclosures allow scientists to compare protected willow growth to stands with no protection. The study results have not necessarily helped to clear up the issue. In fact, some studies have shown little difference in the condition of the willows inside the exclosures to those outside. “”Even after 29 to 33 years of large herbivore protection, there were no new willow recruits or individuals, and no expansion on the edges of the willow stands inside the exclosures.”” ([http://www.nps.gov/yell/nature/nothernrange/ch4a.htm]) Here again, more factors are at play than the animals which eat the willows. Most obvious would be the recent drought. However, other factors, such as insects, are also suspect.
One way or another, there seems to be evidence that the moose have reached a food ceiling in several areas. One proof scientists point to is the declining pregnancy rates. Through recent analysis of progesterone levels in moose droppings, scientists have determined the current pregnancy rate in the Yellowstone area is averaging about 75% – compared to 90% in 1966. With such a decrease in the reproduction rate, animal morality will continue to out-pace animal reproduction.
The premature death of older moose is being taken as further proof of the suspected over abundance in the greater Yellowstone and Grand Teton areas. In seasons of food shortage, the old, the weak, and the young are always the first to go. Scientists have documented the death of several older cows in the last few years, strengthening the plausibility of the starvation theory.
Hunting, of course, has an impact on numbers as well. However, as the greatest decline is occurring with the National Parks which do not allow hunting, this factor would seem insignificant. The number of permits issued outside the Parks is determined by the best estimated moose numbers. Therefore, hunting would not seem to be a viable reason for the current decline. Although most certainly it has had an impact in the past – and therefore has possibly had an effect on where the numbers are today – it seems unlikely this is still a precipitating issue.
Another possibility, which would explain the dropping numbers, is the moose are just moving to other areas. Certainly they have moved in the past. Although it is possible they were residents of Yellowstone’s northern range before 1882, they were conclusively identified as residents by 1913. Obviously these animals moved to our area from somewhere else. Is it possible they are just moving from the Parks and the Jackson area to greener pastures – like the Centennial Valley and Island Park? This theory has not been explored to any degree in the reports I have read. However, the difficulty of tracking moose, and their solitary nature, add to the challenge of determining if this is a contributing issues.
Here in the Centennial Valley it is the willows, not the moose, which are declining. Known for many years as one of the best places to view moose, the Red Rock Lakes National Wildlife Refuge is now facing “”Moose”” challenges of its own. On the first refuge moose count conducted in 1944, 35 moose were observed. An ariel count conducted this last winter put the total closer to 130. Home to over 238 species of birds, including the neo-tropical warblers who use dense willow thickets for nesting, the refuge is now facing the challenge of controlling moose populations to protect bird habitat. According to Red Rock Lakes Wildlife Refuge [http://www.redrocks.fws.gov] studies, “”Centennial Valley Moose continue to be managed with little understanding of the consequences or appropriateness of management actions. As a potential major predator of Moose, specifically wolves, colonize the Centennial Valley, an understanding of Moose population demographics, movements, and habitat use will be vital to managing for the combined impact of natural and anothropogenic factors on Moose ecology.”” Wildlife specialists at the refuge have requested funding for increased studies of the moose and their impacts on the local habitat, but to date this funding has been unavailable.
Never an easy issue, the job of protecting all species without over-protecting one species is a challenging one. Those who love the songbirds might be glad to see the moose decline. However, the moose is also an amazing creature which plays an important role in the ecosystem. Moose are considered a ‘keystone herbivore.’ Plant species composition, distribution, and succession are directly influenced by their dietary preferences. This may also influence avian species composition and diversity in areas where moose reside.
On the other hand, those who love the moose might not realize the impact they have on bird habitat. And, finally, those who love the Grizzly and wolf might not realize these top of the chain predators can also become dangerous to the ecosystem if they are allowed to deplete game numbers to such a low point the game animals also become ‘endangered.’ Clearly the desired condition is balance.
Most likely many factors are involved in the situation we find occurring today. As we know, nature tends to cycle. The increase in moose has, at least in some ways, impacted the willows. This in turn has depleted the nesting areas for many bird species. However, with the current decline in moose numbers in many areas, might we not see a corresponding increase in bird numbers? As stewards of this planet, it certainly places a great responsibility on those in positions of authority to use great wisdom in protecting the many plants and animals. As we see an increase in willows, will the Moose return? Or will the continued increase in top of the chain predators in the greater Yellowstone area stymy or possibly even accelerate their reduction? These questions, and others like them, will continue to challenge scientists world wide for many years to come.