Despite warning signs, Tanana Flats moose continue to flourish

Posted: Thursday, June 21, 2001


Clumps of three, four and even five moose stand out like horses in a giant pasture.

There is a moose lying beneath a tree. There are three bulls and two cows standing in a flat area the size of a small parking lot. There is a cow with a yearling calf standing nearby. There is a cow with a bright red newborn calf, no more than two weeks old, bouncing behind it and desperately trying to keep up with mom. There are two trumpeter swans nesting in the middle of a pond surrounded by five moose.

With their winter coats faded brown and white, the moose stuck out against the greening canvas of the flats. In an hour or two of flying, Valkenburg often sees more moose than many Alaskans do in a lifetime.

''Sometimes you come out here and they're lined up like cattle at a feed trough,'' said Valkenburg, a wildlife biologist for the Alaska Department of Fish and Game.

Some of the moose turn and run at the sound of the plane while others simply look up and go back to grazing on willow branches or sedges.

The Flats, a giant, 2,000-square mile puzzle of swamp, bog, water and trees just south of Fairbanks across the Tanana River, is a prime calving area for moose each spring. Some migrate to the Flats from as far away as the White Mountains to the north and the Alaska Range foothills to the south.

''This area is as important to the Interior moose population as the Arctic National Wildlife Refuge is as a calving area for caribou,'' Valkenburg said as he flew over the Flats spotting moose. ''From around us as far as you can see moose move into here to calve.

''They come out of the Chena and Salcha river drainages, they come down from the White Mountains, they come up from the Alaska Range foothills,'' he said. ''I don't think most people in Fairbanks realize how important this area is. It's like a moose refuge with hunting allowed.''

In many ways, a moose couldn't ask for a better living conditions than the Tanana Flats, especially after breakup.

''There's a lot of aquatic vegetation out there,'' Valkenburg said. ''It's a flood plain so there are a lot of lakes and potholes. The first thing moose like to do (in the spring) is feed on sedges around lakes and there's a lot of that out here.''

Biologists estimate there are about 10,000 moose roaming the flats, the equivalent of about one moose per square mile. It is one of the most heavily hunted areas for moose in the Interior. Hunters harvest about 650 moose a year from Game Management Unit 20A, about half of which is the Tanana Flats.

But for the last five years, there have been biological red flags popping up in the Tanana Flats. Pregnancy and twinning rates, two of the prime indicators of a moose population's health, have declined dramatically, leading biologists to believe that the herd is nutritionally challenged and could be just one bad winter away from collapse. Biologists have been waiting for the population to crash for several years but it has remained stable at about 10,000 moose for the last 10 years.

''This is probably as high as we want to see it,'' Valkenburg said of the moose population.

Indeed, the Tanana Flats moose population is somewhat of a biological enigma at this point.

In a normal adult moose population, about 90 percent of adult cows give birth to calves. In the Tanana Flats this spring, biologists documented a pregnancy rate of only about 60 percent.

''That's really poor,'' said wildlife biologist Mark Keech at Fish and Game in Fairbanks.

In addition, two-thirds of the cows on the Tanana Flats aren't producing calves until they are 4-years-old. Normally, about 30 percent of 2-year-old moose give birth and almost all 3-year-olds get pregnant.

The Tanana Flats also has the lowest twinning rate of any moose population in North America. This year, only one in 45 cows gave birth to twins, a measly 2 percent.

Despite all of that, the population remains stable. The herd has a respectable bull-to-cow ratio of 30 bulls per 100 cows, considered high for a population that receives as much hunting pressure as the Tanana Flats.

''It's real uncommon to attain the moose densities we have in (the Tanana Flats),'' Keech said. ''It's even more uncommon for them to sustain that density for as long as they have.''

The low twinning and pregnancy rates are an indication that moose aren't getting enough to eat, biologists said.

''Typically cow moose have their first calf when they're 3 but most moose in the Tanana Flats don't produce calves until they're 4 years old,'' Valkenburg noted. ''They're delaying reproduction a year because they're not in good enough condition to get pregnant.

''If they don't gain weight fast enough they don't get pregnant,'' Valkenburg said.

Studies using an ultrasound to measure fat on the rump of moose have shown that only cows in exceptionally good shape have twins, biologist Rod Boertje said.

''The highest rump fat values in March are those moose that have twins,'' Boertje said.

Biologists don't know what the problem is in the Tanana Flats. It could be that there are too many moose competing for what has become a stagnant food supply because of the lack of wildfire in the area for the past two decades.

The last major fire to sweep through the Flats was the Blair Lakes fire about 20 years ago. Without fire to rejuvenate the country, it is turning into old growth such as aspen, birch and spruce.

''We want to take areas that aren't producing anything except red squirrels and spruce grouse and produce moose,'' Boertje said.

Moose rely on new growth, mainly willow, to get the nutrients they need to get pregnant and survive the harsh winters in the Interior. But without fire, which results in the production of willows, food production hasn't kept pace with moose population.

''If they're eating all willows, eventually alders and birch will replace the willow,'' Boertje said. Birch and alder aren't as nutritious for moose as willows because they contain chemicals that inhibit digestion, he said

''Willows is what we want,'' Boertje said. ''If you get burns you're going to get willows coming up.

''Unless we get some good burns out there we don't want to see any more moose,'' he said. ''The moose on the Flats could really use some help right now. They need some food.''

Fish and Game has been trying to burn a 50,000-acre chunk of the Flats west of the Wood River for the last five years but Mother Nature has conspired against the controlled burn every year. Either weather conditions have not cooperated or the Division of Forestry has been too busy fighting fires elsewhere in the state to supply the resources for a controlled burn of that size. The area to be burned is ''a black spruce monoculture,'' Boertje said.

Biologists have been studying Tanana Flats moose since the mid 1970s.

''It is one of the real long-term moose research projects in the world right now,'' Valkenburg said.

Based on anecdotal information from retired biologists, the number of moose in the Tanana Flats in the 1960s was as high as 20,000. But the population crashed down to 2,500 in the early 1970s as a result of several severe winters and high predation.

State wolf control efforts in unit 20A from 1976 to 1982 boosted the population back up to 6,000 and the herd continued to increase without wolf control to its current estimate of 10,000 to 12,000. Biologists don't know how many moose the Tanana Flats can support.

''Everybody talks about carrying capacity but it's really hard to figure out what it is,'' Valkenburg said. ''We've had winters just as severe in the early 90s as they had in the '70s and the population has remain untouched.''

Biologists have put radio collars on about 130 moose on the Tanana Flats over the last few years. The collars allow biologists to track the moose and figure out everything from pregnancy rates to twinning rates to calf mortality to winter kills.

''With all those animals collared we're in a good position if the population crashes to figure out what causes that decline, whether it's predation, habitat or weather,'' Keech said.


(Distributed by The Associated Press)

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