Browsing for answers to moose populations

Biologists determine well-being of animals by studying food sources

Posted: Sunday, May 20, 2007

FAIRBANKS - Walking through the woods off the Steese Highway about 20 miles north of Fairbanks, Tom Paragi and Don Young were glad they weren't moose.

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"You'd want to pack a lunch if you were a moose walking through this area," said Paragi, a wildlife biologist for the Alaska Department of Fish and Game in Fairbanks. "There's not a whole lot of food here."

Young, a fellow biologist, pointed to the stems of several wild rose bushes that had been cropped by moose.

"You can see where they're browsing rose bushes," he said.

That didn't surprise Paragi.

"They'll browse prickly rose," he confirmed. "When they move through they'll eat whatever they can get."

Surveying a plot of woods just the day before, Paragi had seen where moose had been eating highbush cranberry and soapberry plants.

"Typically when they've got a lot of food available they don't browse those species," he said.

In this particular patch of woods, though, there wasn't much food to be had.

"Most of these willows are dead in here," said Paragi. "Looking at the size of the spruce and birch trees, I'd say this stand is probably 100 to 150 years old. This is going to be a spruce stand over time."

Moose don't eat old spruce trees. Moose eat young willow, birch and cottonwood plants, preferably the thin, tender shoots that grow from one year to the next, which is what Paragi and Young were looking for on this particular day last month. There were only a few willows on the site and none of them fit that description.

"This is probably a 50-year-old willow," said Paragi, standing in front of a 30-foot tall willow. "There's not a lot of food on this tree."

There were a few stems that a moose could have stopped to eat but they hadn't. Using a pair of calipers, a pliers-like instrument used to measure the diameter of twigs, Paragi related the measurements to Young, who jotted them down on a clipboard.

The two wildlife biologists were conducting a moose browse survey in Game Management Unit 20B around Fairbanks. Browse surveys are one of a handful of tools that biologists use to gauge the nutritional status of a moose population.

Using randomly selected plots of woods off the road system within a 45-mile radius of Fairbanks, the biologists were checking to see how much food was available for moose and how much food they actually ate over the winter.

Biologists count the number and type of browse species available in a plot, which are 30 meters in diameter, and then determine whether or not they have been browsed and how big the new growth stems are. Moose typically feed on stems that are about one-eighth of an inch in diameter because those are the most nutritious. Anything bigger contains more wood than bark and takes more effort to digest, which at 30 and 40 degrees below zero, costs the moose as much energy as it gains from eating it.

By looking at the type, size and quantity of forage moose are utilizing over a large area, biologists can determine what kind of shape they are in and how to better manage the population.

"If you do that on thousands of twigs spread across the countryside, you get a good idea of what's going on," said assistant area management biologist Tom Seaton, who spent two years studying the relationship between browse and a growing moose population in Unit 20A south of Fairbanks for his master's thesis several years ago.

For example, the state instituted a liberal antlerless moose hunt in Unit 20A three years ago after Seaton's and other studies showed the moose population was on the verge of nutritional collapse. As a result, hunters have killed almost 2,000 antlerless moose in Unit 20A the past three years and the department is planning another big cow hunt this season. The population is just beginning to show signs of increased productivity.

"We're convinced those populations are growing rapid enough and we don't want more moose in those areas," state Wildlife biologist Rod Boertje said of Units 20B and 20D. "We know what the nutritional status will be like if we let it grow."

The state has also initiated predator control programs in several areas around the state to boost moose and caribou populations that have declined. In those areas, twinning rates and browse surveys indicate there is plenty of food for moose to eat but predators are killing them before they can eat it.

Boertje, who has worked as a biologists for almost 30 years in Fairbanks, spent the last two years writing a paper titled "Ranking Alaska moose nutrition: signals to begin liberal antlerless harvests" that will be published in the Journal of Wildlife Management next month. Using nutritionally-influenced factors such as twinning rates, age of first reproduction, yearling weights and percentage of browse biomass, Boertje ranked 15 units around the state.

Not surprisingly, the units that had the healthiest moose also had the fewest. Unit 17 in Southwest Alaska (Togiak) ranked No. 1 on the list with a twinning rate of about 67 percent, followed by Unit 24B (Yukon Flats), Unit 20C (Denali Park) and Unit 19D (McGrath), all of which have twinning rates of more than 50 percent.

"We decided once and for all we'd try to rank the nutritional status of moose in Alaska, from the very best to the very worst," Boertje said. "We're continually attacked that we don't have enough science; this is the science."

As a result, the department has developed four criteria that serve as trigger points for instituting large antlerless harvests: 1) a twinning rate of less than 10 percent; 2) a browse biomass removal greater than 35 percent; 3) yearling weights less than 385 pounds; and 4) less than 50 percent reproduction rate for 3-year-olds.

Twinning rates are the best barometer of the nutritional shape a moose population is in, according to biologists. The healthier and fatter cow moose are when they are bred in the fall, the better the chances are they will produce twins.

Moose in Unit 20A are in the worst nutritional shape of any moose population in North America, said Boertje. At an average of 7 percent, the twinning rates are the lowest in the state. The unit also has the highest percentage of browse removed by moose.

Biologists estimate that moose eat 43 percent of the browse available in Unit 20A, which is more than twice what the percentage is in any other part of the state. Conversely, the twinning rate in the Yukon Flats north of Fairbanks, a notoriously low-density area for moose, is 64 percent while only 9 percent of the available browse is removed each year.

"The lower the browse biomass removal, the higher the twinning rates," Boertje said.

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