A grasp on elusive red voles
(This is a copy of a story that appeared at http://www.oregonnews.com/1.news/09.13.news1.html)
Biologists study the tree-top mammals nest sites, DNA to determine habitat needs
BY GARRET JAROS
September 13, 2000
GLIDE Shafts of sunlight angle through the treetops, producing rays of prismatic colors as biologist Eric Forsman grips a dead limb and begins to climb toward the nest of a red tree vole.
The Northwest Forest Plan requires agencies to survey for the red tree vole, even though it is not a protected species in Oregon, before beginning any forest projects. Because very little is known about the vole, biologists are trying to determine if the vole lives solely in old growth forests or if it also thrives in younger stands.
A strategic survey is being conducted this summer on the Umpqua National Forest, Roseburg Bureau of Land Management lands and the Klamath National Forest in California. Nearly two months into the survey, biologists are finding enough evidence to indicate the voles are abundant.
Forsman makes quick work of his climb ascending hand-over-hand 30 feet to the nest, his lithe body supported by limbs brittle enough to snap.
Be ready, he calls down to fellow biologist Brian Biswell, who cranes his neck and looks up from the base of the tree.
When a red tree vole nest is disturbed, the hamster-like creature will often leap for the ground. Forsman begins rummaging through the nest, a beaver dam like collection of twigs and discarded fir needles that nearly circle the trunk of the 35-year-old Douglas fir.
The Oregon red tree vole is unique among mammals in that it spends most of its life in the canopy of coniferous trees and eats needles of conifer trees. It is the most arboreal mammal in the Pacific Northwest.
Red tree voles live only in the Cascade and Coast Ranges of western Oregon, and because they spend most of their lives in the forest canopy they are difficult to study.
Biologists began surveying for the voles July 15 and will finish at the end of September. The results will be written up in the fall and winter and then be used for management decisions.
Forsman and Biswell, both Forest Service biologists with the Pacific Northwest Research Station in Portland, are guiding three teams of three people as they search for nest sites and collect DNA samples. They will also look for the remains of voles in owl pellets while other teams map the vegetation types where nests are found.
This is the central part of their range, probably the best range along with the Coos Bay BLM lands, Biswell said of the Umpqua basin. Well survey 70 to 75 stands on Umpqua and BLM lands.
The red tree vole was placed on the list of creatures to survey for because theyre most abundant in old forests and not much is known about them.
You cant jump to conclusions just because theyre on that list, said Forsman, who helped comprise the list.
Past forest management practices have fragmented and converted old growth, or late-successional forests, to young, even-aged forests which is believed to have reduced the number of red tree voles.
Because of the limited range of the vole, females usually move only 15 meters from one nest site to another. Voles travel from treetop to treetop, but on rare occasions will travel on the ground when no other trees are nearby.
At the nest site, Forsman finds vole feces, which he preserves in a plastic vile so it can be tested for DNA if no vole is found. Then he comes across a surprise squatter, a pinkie-sized salamander. He puts it in a plastic bag and drops it to Biswell. Salamanders and tree frogs will often seek out vole nests for their moisture.
Suddenly it happens.
Here comes one! Forsman shouts. Get ready! A rusty cinnamon vole runs down the trunk toward Biswell, pausing for an instant before jumping. Biswell catches the critter against his chest and uses his thumb and forefinger to grab it by the scruff of its neck so it cant bite.
It chatters loudly and shakes furiously while Forsman makes his way back down the tree. The biologists work quickly. It is a post-lactating female. Forsman holds the voles tail with forceps and slices off the last quarter inch with a razor knife. The sample will be used for DNA testing. The tail will not grow back, but it does scab quickly.
From that we get some idea whether or not there are genetically distinct local groups of tree voles, as opposed to a fairly well-mixed gene pool, Forsman said. The idea is to find out if we have to be concerned with genetically distinct pockets of tree voles or whether theyre pretty well mixed.
Whether tree voles are able to travel through younger stands of trees is what biologists are trying to understand.
To say they dont disperse through younger stands at all is flat wrong because were finding them in those stands, Forsman said. My study is somewhat biased because in younger stands its easier to get in, but of the 12 voles weve captured this year, most were found in younger stands.
In older stands, biologists find more nests, but not necessarily more voles.
Very few nests in old or young do we find live tree voles. I dont know what to make of that yet, Forsman said. I have to climb about 40 nests for every vole I catch.
In most nests he finds only fecal material.
The red tree voles range extends from the Columbia River south almost to the San Francisco Bay and includes more than 13 million acres in Oregon, 35 percent on federal land. It is an endemic species that only occurs in the Pacific Northwest in Oregon and California, where it has been a sensitive species since 1991.
It is the primary prey species for the northern spotted owl as well as other owls, weasels, fishers, martens and ring tails.
Voles eat their body weight, about 28 grams for an adult female, in conifer needles a day. They live to be about a year old and dont breed as often as other mice species. No one knows how many litters they have, but they are capable of reproducing multiple times in a year. They will normally have two to three young.
The biologists have come to some conclusions this summer.
In general, the impression here is we have a lot more old unoccupied nests then we do in the coast range, Biswell said. We dont know why yet.
But Forsman believes there are plenty of voles out there.
I dont think theyre rare in this area, Forsman said. When you find them in 14 percent of regurgitated owl pellets that suggests the voles arent that rare. They cant be and show up in that big a proportion of owls diet.
You can reach reporter Garret Jaros at 957-4218 or by e-mail at firstname.lastname@example.org.