Anchorage Daily News

Voles were marching on the mudflats. Dodging merlins and weasels in town. They were, that is, until a protective blanket of snow finally concealed their burgeoning numbers last week, local biologists say.

Now the plump country cousins of common house mice are out of sight once again -- safely tucked into their familiar, low-ceilinged "subnivean space" between old grass and new snow, where they remain active all winter long.

This year that space might get crowded. Anecdotal reports indicate that Anchorage area voles -- one of the most prolific mammals in the world -- are nearing the peak of their local population cycle.

"I've seen quite a few (voles) myself, and I've seen a lot of vole predators too," like ermine and hawk owls, state area biologist Rick Sinnott reported a day before the snow fell.

"That's usually a sign. We have eruptions of those owls from up north when we get a lot of prey animals down here."

Prey with no place to hide. By mid-November the leaves had blown away, along with much of the snowpack, leaving voles easy targets for coyotes, owls and weasels.

Walking along the beach that borders the Anchorage Coastal Wildlife Refuge a few weeks ago, South Anchorage resident Lorvel "Smiley" Shields -- who studied mice and voles as part of his doctoral research years ago at UCLA -- marveled at all the vole tracks.

"It's unusual to see (them) out that far from the bluff," he said. But the tiny footprints appeared to vanish near the water. A mass suicide? More likely a meal for some predator, Shields said.

"They would have had no cover whatsoever. The voles that were out there were just dead meat."

LITTLE VOLE CITIES

What a difference a few months makes. In late summer, voles were living large in the gardens and grasslands around Hope, on the south side of Turnagain Arm, according to local residents.

It almost felt like an organized assault, said Dr. John Christopherson, an Anchorage pediatrician who's summered at Hope for more than 30 years.

"There seemed to be areas where they were developing little colonies, almost like metropolises," Christopherson said. The voles devastated his potato crop and pocked his garden with burrows. Some were walking boldly across the road.

"They were doing these big excavations and you just knew there was a little vole city down there," he said. "It was a little bit of the Alfred Hitchcock 'Birds' sort of thing."

Wildlife populations naturally rise and fall. Sometimes there's a pattern, biologists say. For snowshoe hares, the cycle repeats itself every 10 years or so. Suddenly snowshoe numbers explode. Then the lynx that feed on the hares respond with larger litters, until eventually the prey subsides.

But voles (there are about five species in Alaska) are different, says Shields. Their populations appear to rise and fall more sporadically in isolated pockets, depending on local conditions. And a vole boom on one side of town doesn't necessarily guarantee the same on the other side.

But when vole numbers erupt, they really erupt, Shields said.

"Every species has its own (survival) strategy, and voles do that by just turning out so many babies that some of them live," he said.

The meadow vole, Microtus pennsylvanicus -- the most widespread vole in America, with a range that extends from the East Coast to Alaska -- can give birth to a new litter within a week of weaning an earlier litter, according to "A Complete Guide to Arctic Wildlife," by Richard Sale. (One meadow vole in captivity had 17 litters in a single year, Sale said.)

"From the time they're a single cell to the time they start having their own babies is something like a month and a half," Shields said.

MICE V. VOLES

Still, voles aren't that likely to end up in your home, he said. That's generally the province of house mice, which are smaller than voles. House mice have protruding ears, like Mickey Mouse, whereas a meadow vole has ears that hug its head.

But Shields also can tell the difference from the droppings they leave behind. House mice tend to leave multiple droppings, like dark versions of thin, long-grained rice. Voles tend to leave shorter, rounder and fewer droppings. Usually they're found outdoors.

"Voles already have what they want to eat out in the woods. They're not looking for high-protein stuff. They're just looking for grasses they can process in a hurry."

Voles that dawdle over their meals don't live long. Given that they're virtually at the bottom of the mammalian food chain, nearly every carnivorous animal on four legs is trying to eat them (even the tiny shrew -- an insectivore several times smaller than voles). Let alone all the predators with wings.

During the summer, a pair of merlins built a nest in the center of Hope, and fed its three hatchlings on voles all summer, Christopherson said.

According to the most recent report by the Anchorage Audubon Society, birders in November spotted several other vole-hunters within city boundaries, including a short-eared owl, an American kestrel and a sharp-shinned hawk.

On the North Slope around Barrow, periodic eruptions of lemmings, a close cousin of voles, result in a welcome banquet for snowy owls and jaegers, says Audubon Alaska executive director Stan Senner.

"That's a big, big deal to the birds that are there," Senner said. "Then life is also good for smaller birds that otherwise get eaten."

Whether the vole boom around Anchorage has attracted more raptors to town probably won't be known until Audubon conducts its annual Christmas Bird Count in three weeks, Senner said.

In the meantime, vole hearts are happy, safe beneath the snow.

Find George Bryson online at adn.com/contact/gbryson or call 257-4318.