KENAI (AP) -- The man and woman walked into a snowy clearing. A cow moose paused and lifted her head, then turned and approached the intruders.
She walked right up to the man, thrust her nose up to his parka and sniffed intently. ''Hello, Willow,'' he said, reaching out and scratching her shaggy neck.
The man, Tom Stephenson, is a wildlife biologist with the Alaska Department of Fish and Game and head of studies at the Kenai Moose Research Center.
The woman with him was Stacy Jenkins, a graduate student from Washington State University. They are studying moose nutrition to find out why moose populations change and what people can do about it.
''It all relates back to carrying capacity,'' Stephenson said. ''How many animals can the range support?''
The question is particularly relevant these days on the Kenai Peninsula, where moose numbers are declining. Scientists believe humans indirectly caused the change.
From about 1900 to 1950, settlers triggered forest fires that destroyed vast acreage of native forest on the peninsula. In the decades that followed, young hardwoods sprung up in the burns. Moose thrive on young, low growth of willow, aspen and birch.
The new growth converted the peninsula into a moose's paradise. But now those trees are getting too tall for moose to reach the tasty twigs.
''We know the forest has really matured and supports fewer moose than 20 or 30 years ago,'' Stephenson said.
Wildlife managers want to make sure that people do not inadvertently set the moose up for a disaster by encouraging their population to get too high. The big deer could overgraze their range, decline in health and become vulnerable to other threats.
''Populations can crash,'' he said. ''All of a sudden you throw a severe winter in there, and the population can nose dive, and you don't have enough to recover.''
The biologists have been checking the physical condition of moose around the state. Whenever and wherever they tranquilize an animal to put a radio collar on it, they measure it, take blood samples and check the thickness of its body fat.
The health of the moose herd varies around the state. Moose on the densely-populated Tanana flats are in poor condition. Moose in Denali National Park are thriving. Prime animals are found east of Cordova.
''The Copper River Delta is really the gold standard for what a moose population can do,'' Stephenson said.
Ferreting out exactly what moose need for a healthy diet has proven a tricky puzzle for the biologists. They have been pursuing the topic for decades at the research center.
That is where Willow and the rest of her four-legged colleagues come in. Twenty-six moose live at the center, roaming in four square miles of enclosures in the Kenai National Wildlife Refuge near Swanson River north of Sterling.
Founded in 1968, the center hosts much of the world's leading moose research. The facilities are owned by the U.S. Fish and Wildlife Service, staffed by state Fish and Game and run cooperatively by the two agencies.
The moose at the center are habituated to humans. Many orphan moose calves Alaskans find in the spring end up at the center, bottle-raised from infancy and handled as they grow.
The center has set up three different moose habitats. One has been heavily browsed for a long time. The other two had been spared grazing until recently. One of those has a mature forest with tall trees and little undergrowth. The trees in the other were crushed in the late 1980s and allowed to regrow with brushy young hardwoods.
Jenkins is one of the people studying how the moose interact with the plants. She is looking at what the animals are eating, the size and shape of the saplings and the effects of grazing.
''When you spend enough time out there, you can predict what they are going to take,'' she said. ''There is a pattern.''
She spends hours in the cold winter woods, following moose and noting into a hand-held field computer what type and size of twigs they eat, how often they eat and what they do when they are not eating. Sometimes she even goes back and measures the diameters of the gnawed stems left behind.
Their findings show that the smallest, newest twigs are the most nutritious. Moose may even improve their own browse by pruning bushes back and breaking the tops off saplings so the plants take longer to grow out of reach.
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