Moose's winter diet pretty plain

Bland browse

Posted: Friday, January 17, 2003

FAIRBANKS -- How much wood could a cow moose munch if a cow moose could munch wood?

Well, moose do munch wood and they munch lots of it during the winter, as a matter of fact.

Of course, that's about the only thing moose eat during winter in Alaska, unless they stumble onto the remnants of a vegetable garden or happen onto a hayfield that isn't buried in snow.

Moose rely almost solely on twigs from birch, poplar and willow twigs in the winter.

''The bark is really what they're after,'' said state wildlife biologist Tom Seaton, who recently spent two years studying moose browse in the Tanana Flats for his master's thesis. ''Wood is not digestible to moose.''

And even though they eat 20 pounds of food a day, the average adult moose in the Interior loses about 25 percent of its body weight during the winter. That means a moose that weighs 1,000 pounds in October will slim down to about 750 by April.

''There's not a maintenance diet to be had here in wintertime,'' said Terry Bowyer, a professor of wildlife biology at the University of Alaska Fairbanks. ''They're losing weight all winter.''

Basically, a moose can't eat enough during the winter to maintain its body weight. Imagine what would happen if you ate only pretzels and bran cereal for six straight months and all you had to wash them down with was snow that you ate?

''The standard diet a moose has in winter will not meet its energy needs,'' said state wildlife biologist Kris Hundertmark at the Kenai Moose Research Station on the Kenai Peninsula. ''The diet is so coarse and fibrous they have to spend a lot of time digesting it.''

Moose are similar to bears in that they spend the summer and early fall trying to eat as much as possible in an effort to put on fat for the winter. But instead of hibernating, moose spend the winter roaming around the woods in search of food.

''Moose have a very short period of time to make and store fat ... that's during summer,'' said Hundertmark. ''They become eating machines in the summer.''

Interior moose spend approximately five hours a day eating during the winter, said Hundertmark. That's about half of the time they spend feeding in the summer (an estimated 9.5 hours in July).

''In winter they are energy conservation machines,'' he said. ''The more time they spend out feeding is counterproductive. They're expending more energy than they're taking in.''

But finding food in Alaska during winter, especially when there is deep snow and it's 30 below, is hard work and burns valuable calories.

The general theory is that a moose eats about 3 percent of its body weight in dry food during the summer and about half of that in the winter.

That means a 1,000-pound moose eats about 30 pounds of dry food in the summer and about 15 in the winter.

A moose's diet during the summer contains about 15 to 18 percent protein, he said. In the winter, the protein content drops to 6 or 7 percent.

''That's a huge difference,'' Hundertmark said. ''Even though they can take in the same amount of material it's got much less protein in it.''

When a moose uses up its store of fat reserves, it's in trouble. ''Once they get down low enough, they'll start consuming their own muscle mass,'' said Seaton.

When that happens there's a good chance a moose will starve if green-up isn't right around the corner. Even on a good winter diet, moose can't consume enough calories to keep them alive if they don't have any fat to lean on.

''That's the point of no return,'' Hundertmark said, referring to the point when moose begin relying on muscle instead of fat to survive. ''It's like having a bank account. Moose earn money all summer because they're taking in more energy than they're expending.

''They draw on that bank account all winter long hoping it lasts until the spring because if it doesn't they die,'' he said.

Moose calves are especially vulnerable to winter starvation because they don't have the fat reserves adults do going into the winter.

Calves allocate most of their food intake to growth and come into the fall much leaner than adults.

''Adults can handle it down to 40 below without raising their metabolic rate and stay warm,'' said Hundertmark. ''Calves lose a lot of energy when it's below zero.''

Moose do eat other things besides branches in the winter, if they can find them. In years with low snowfall such as this one in the Interior, moose will dig up low-bush cranberry bushes and eat them.

It's also common to see moose kneeling on their front legs feeding on grass they dig up in yards and hayfields. Flower and vegetable gardens are also considered delicacies.

''Every year before the snowfall I've got moose in my yard eating clover on their knees,'' said Hundertmark. ''It's the last thing out there that resembles protein.''

Moose will do whatever it takes to find the best food, too.

''They'll bust off taller willows and birches to get at the more succulent forage,'' said Bowyer, the UAF professor. ''They'll walk over it with their chest to bend it down or grab it in their mouth and break it off. I've seen them do both.''

The average size of twigs that moose eat during the winter is 3 millimeters in diameter, or one-tenth of an inch, Seaton said. The hungrier they are, the bigger the branches they will eat. About the biggest twig a moose will eat is one-quarter of an inch, Seaton said.

''If they're nutritionally depressed, they'll eat larger diameter twigs,'' Seaton said.

They get in trouble doing so, however, because bigger twigs have more wood than smaller ones, which means moose spend longer digesting it.

Moose don't die because they stop eating; they die because what they're eating isn't good enough to keep them alive. Even when moose are found dead from starvation, they usually have stomachs full of wood, said Seaton.

''I've never heard of somebody who found a moose with an empty stomach,'' he said. ''They'll eat but they can't digest it.''

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