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Missing moose mystery
As population shrinks, a researcher braves bears and the elements to find out why.

By Rebecca Huntington

As biologist Joel Berger scans radio waves for Natalie's signal, he looks across the Snake River plain near Flagg Ranch and sees a band of elk break into a dead run.

He grabs his binoculars and trains the lenses, not on the half dozen running elk, but on the spot from where they bolted. He wants to see what spooked them. A grizzly perhaps?

No answers are forthcoming from the landscape where only a flock of geese is visible amid the patchwork of meadows, marshes and willows. Forgetting the elk, Berger dons wading boots and strikes out across the same terrain to try to track down Natalie, a radio-collared moose.

Potentially sneaking up on grizzlies is among the on-the-job hazards Berger confronts as he studies the Jackson moose herd. Berger is the only biologist tracking moose in the Jackson Hole area, where his research is taking on increasing importance.

While moose numbers have remained stable across Wyoming, moose counts in Jackson show a sharp decline. Moose numbers dropped to 1,700 this year, down from a high of 3,500 in 1992, according to Doug Brimeyer, a wildlife biologist with Wyoming Game and Fish Department. (Some Game and Fish counts show the moose herd peaking at 5,000, but Brimeyer said such figures are artificially high due to errors in a computer model used to estimate moose populations.)

Nonetheless, the herd's size has been cut in half in a decade. The cause, however, is not entirely clear with biologists positing different theories.

A rebounding grizzly bear population ­ the very species Berger is trying to avoid as he tracks the radio-collared moose ­ could be one reason for the decline. Since 1996, Berger has documented 13 moose killed by grizzlies. He also suspects a grizzly may have been responsible for the disappearance of Natalie's calf last year. Though estimates are vague, counts suggest the greater Yellowstone region's grizzly population has more than doubled to between 400 and 600 grizzlies since the bears were protected by the Endangered Species Act in 1975.

But while bears are a factor, focusing on predators misses the real problem, Berger says. Starvation is the leading cause of death in his study.

Since 1994, Berger has fitted about 95 moose with radio collars. Of his collared moose that have expired, about 60 percent starved to death, which is high compared to other herds, he said. In contrast, the portion of moose killed by grizzlies ranges from 10 percent to 16 percent, and wolves account for only 2 percent of adult moose deaths.

Moose in the valley may have hit a "food ceiling," with deteriorating and diminishing habitat now dictating moose numbers, his study suggests.

Two other factors also point to habitat as a cause of declining moose numbers, he says. Pregnancy rates among moose have declined to between 60 percent and 80 percent, compared to 90 percent in the 1960s. Also, less than five percent of moose give birth to twins. Other studies link abundant food with higher twinning rates, he says.

"The high rates of starvation, the low twinning rates and the low pregnancy rates indicate a population experiencing food limitations," Berger says.

But Brimeyer interprets Berger's data differently. Although low, pregnancy rates have remained steady over the past decade while the number of calves surviving has declined, which Brimeyer says suggests a predator problem.

To get a more definite answer, Game and Fish is seeking grants to expand Berger's study by radio collaring and tracking an additional 10 moose in Buffalo Valley where plummeting moose numbers are most noticeable. During the past few winters, Game and Fish counted as few as 123 moose, less than half the average of 335 moose counted in Buffalo Valley during the late 1980s.

While Berger is tracking moose across Grand Teton National Park and the adjacent Bridger-Teton National Forest, Game and Fish's proposal would focus data collection on moose deaths and pregnancy rates in Buffalo Valley and the adjacent Teton Wilderness, which is home to a rebounding grizzly population. Game and Fish counted 36 grizzlies north of Togwotee Pass during four research flights in 2001.

Although Natalie occupies the John D. Rockefeller, Jr., Memorial Parkway between Yellowstone and Grand Teton, her home range is near the Teton Wilderness and illustrates some of the challenges researchers will face tracking moose in grizzly country.

On an outing in late May, Berger creeps as quietly as humanly possible through head-high willows. Typically, the rule of thumb in grizzly country is make as much noise as possible to avoid surprising a bear. But if Berger makes too much noise, he'll spook Natalie, who is known to run from humans.

So Berger carries both pepper spray and his radio antenna, which picks up the radio collar signal, in the same hand. He uses the other hand to adjust the dial on a receiver at his hip.

"This is just like tuning in a radio station," he says, adjusting the dial. "Each one has a different frequency."

For the past nine years, Berger has been tracking between 15 and 20 radio-collared moose from the southern end of Yellowstone National Park to Jackson. He began studying Jackson's moose while working as a professor at the University of Nevada, Reno. He now works as a senior scientist for the Wildlife Conservation Society and lives in Teton Valley, Idaho.

Berger is tracking Natalie to see whether she has given birth. He knows she is pregnant from hormone levels in a feces sample he collected from her previously. Berger wants to document whether a calf actually hits the ground as part of his research on pregnancy and calf survival rates.

Berger acknowledges giving his research subjects names is unconventional.

"I didn't name these, my wife did," Berger says. "I used to have numbers like a real biologist."

But naming the moose makes it easier to remember their personalities, which Berger says helps him predict their behavior. The pepper spray is not just for the grizzlies. Berger has been charged by moose and wears a whistle around his neck as an added precaution. The sound of the whistle in combination with pepper spray has stopped a moose charge, he says.

Since he is following Natalie's radio signal, he cannot simply take the path of least resistance. The moose's signal forces Berger to wade through hip-deep, ice-cold water.

On this day, Natalie eludes Berger because she happens to be on the other side of the Snake River, which is swollen with spring runoff. Two days later, his research assistant will document that she has had twins, a rarity in this area.

Berger is not the first researcher to conclude moose have reached their winter food limit in Jackson Hole.

In the last intensive study of the region's moose completed in 1968, Douglas Houston found that moose numbers fluctuated between 1950 and 1966 based on the quality of the habitat.

Predators were not much of a factor during Houston's study since by the 1960s grizzly were so scarce the species was soon listed as threatened and wolves had been eliminated altogether in the greater Yellowstone area. Game and Fish also believes mountain lion populations were lower at that time though population estimates are not available.

Houston's research showed that weather was a key factor in limiting moose numbers. Snow depths, in particular, played an important role because snow covered up and protected willows by preventing permanent damage due to moose browsing too far down the plant, he found.

Houston's study points out that the moose population expanded during a period of significant, long-term increases in average snow depths with two to three feet of snow covering most winter ranges. He projected that climate change, particularly reductions in snow depths, would significantly alter how moose use willows and thus, the quality of the habitat. His research showed severely over-browsed willows had less regrowth than moderately or lightly browsed willows.

Houston also warned that human activities were hastening the decline of moose habitat. Willows and other riparian plants depend on the cutting action of a river and flooding. Houston predicted alterations to the Snake River, including levees and the Jackson Lake Dam would speed up the demise of floodplain plant communities, which moose favor.

Also, building the Gros Ventre Campground and a golf course along the Gros Ventre River caused a loss of winter moose habitat, he wrote. He also cited competition from cattle and elk as a limiting factor in food available for moose.

Game and Fish habitat biologist Steve Kilpatrick said the agency has not done a comprehensive review of moose habitat conditions since Houston's study, which is one reason the agency is seeking funding to step up moose research. Part of Game and Fish's proposal calls for studying how moose use habitat and whether moose favor areas where fires have improved forage. Also, money would be spent researching Game and Fish files to compile data on habitat monitoring and conditions.

Moose are relative newcomers to Jackson Hole. Trappers and hunters, who kept detailed journals, did not mention moose in this region in the early 1800s. Likewise, moose were not included in the first Wyoming wildlife act, which regulated the hunting of elk, deer, antelope and mountain sheep.

Moose likely migrated to Wyoming from Montana during the 1840s or 1850s, historic journals suggest. One theory is that a reduction in predators allowed moose to expand their range and migrate. The first record of moose in the Jackson Hole area is an 1872 photograph of a moose and calf killed by the Hayden expedition.

Berger's hypothesis is that in the absence of predators moose were able to expand beyond the capacity of the habitat. Moose numbers hit a food ceiling and now are dropping back.

Game and Fish's Brimeyer is more inclined to attribute population declines to predators, such as grizzlies. However, Brimeyer agrees emphasis must be placed on improving habitat, which he says could help offset impacts from predators.

This summer, Berger will keep tabs on the radio-collared moms and their offspring to try to determine the health and survival rates of both adults and calves.

Like adults, many calves starve to death, Berger's research shows. Using photos, Berger gauges a calf's head size as an indicator of body condition. When he has a carcass, adult or baby, he takes a bone marrow sample. If the bone marrow looks like red gelatin, that means the animal's body is consuming the bone marrow ­ a sign of starvation.

Predators also have an impact, but Berger says that impact is often overstated.

Although he documented calves killed by wolves in 1999, he has not seen calves killed by wolves since then. Berger hypothesizes that after the 1999 losses, mother moose became more vigilant about protecting their calves from wolves.

Much of Berger's research focuses on the theory that Jackson's moose are naive about wolves because the predators were extirpated from the ecosystem for more than 60 years. Berger has documented that moose in Alaska, where wolves have been consistently present, react more vigilantly to wolf howls and smells than moose in Jackson.

Naive moose may make easy prey for wolves but will become harder to kill as they learn to fear and avoid wolves, Berger's research suggests. Also, extensive tracking of wolf kills in Yellowstone show wolves primarily prey on elk and kill few moose. Researchers in Yellowstone are stepping up efforts to collect more data on wolf kills during the summer season when moose calves are most vulnerable.

Based on Berger's research, grizzlies are more significant in moose predation than wolves.

In addition to starvation and predators, moose die for a number of other reasons, including collisions with motor vehicles. During the winter of 1997, 11 moose kills were documented along a five-mile stretch of Highway 390, according to Brimeyer.

Game and Fish has not determined how big of a problem road kill is for the herd as a whole, but it is a significant source of mortality in some locations, he said.

Yet another cause of death is detected among Berger's collared moose during the recent May outing. After Berger gives up the search for Natalie and heads south from Flagg Ranch, he receives a call about a dead moose near the Teton Science School in Grand Teton.

He finds the carcass in cottonwoods near Ditch Creek. She died either the night before or that morning because rigor mortis has not set in, he says, examining the mostly intact body. Scavengers have eaten portions of her rump and neck.

Nothing indicates predators were the cause. No bite marks or puncture wounds are visible. Berger's assistant cuts off the jaw as a sample. She had only one, worn-down tooth, suggesting she was old.

Berger concludes she died trying to give birth. Fetal bones at the scene show that she had a calf, but plastic-like tissue on the calf's hooves indicate it never stood up. Brown, matted grass around her body indicates she labored in the area for some time, Berger says.

This is the third moose death due to childbirth Berger has documented. The remains illustrate the range of factors that could be affecting the Jackson moose population ­ in this case, aging moms.

Says Berger: "This is why it's so complicated. It's not necessarily a single cause."

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