Game Commission Photo

By Joe Kosack, Wildlife Conservation Education Specialist, Game Commission

Most people live their lives without ever seeing an Allegheny woodrat. And they probably are ok with that, with rats being rats and all that. But this rat isn't a "rat."

Woodrats are important to Pennsylvania, according to the Game Commission, and research is now underway to improve management of this state-listed threatened species.

"Woodrats, like bald eagles, are one of our best and last indicators of true wilderness," said Carl G. Roe, Game Commission executive director. "They are confined to Pennsylvania's ridges, and, as those ridges are developed, woodrat communities often become ghost towns, historical markers of what once was. Most people won't miss them. In fact, most didn't even know that they were out there. But woodrats are significant. They are a species of greatest conservation concern that the Game Commission's Wildlife Action Plan has designated as in immediate need of assistance."

A three-year study, partially-funded by a Game Commission State Wildlife Grant, and being led by Indiana University of Pennsylvania (IUP), is attempting to shed light on the daily and seasonal movements of woodrats, a largely nocturnal member of the state's wildlife community that spends considerable time in subterranean settings. The fieldwork also will attempt to identify high-quality woodrat habitat on the Chestnut Ridge of the Allegheny Mountains in Indiana and Westmoreland counties, and shed more light on woodrat demography, as well as ascertain whether providing food caches can bolster a woodrat population in decline. Work will include radio-telemetry, DNA profiling and mark-recapture trapping.

The wood rat shouldn't be confused with the Norway rat, the world's proverbial poster critter of filth that originated in northern China and now inhabits every continent - as well as every Pennsylvania county. At one time, woodrats were found in 41 Pennsylvania counties, but the 20th century's American Chestnut blight and gypsy moth invasion - also oriental imports - and substantial changes in land use have conspired to create huge habitat deficiencies and insurmountable barriers in the woodrat's world. Today, woodrats can be found in a couple dozen or so mountainous counties, and their population centers usually are surrounded by vast stretches of inhospitable and uninhabitable lands that they have little chance of traversing to reach other woodrat-friendly environs.

Woodrats, which live a relatively solitary existence, prefer rock outcroppings and cliffs, talus slopes, boulder-covered ridges, caves and mines. They generally are found at higher elevations and, according to Dr. Joseph Duchamp, who is leading IUP's research team in the field, the distribution of woodrat activity centers in the area where fieldwork is occurring surprised him somewhat.

"The way they have these pocket populations scattered throughout this slope, and the area covered by some of these specialized habitats was more than I expected," Duchamp explained. "We're eager to learn more about how these small populations interact and to determine if they're connected by subterranean passages."

Duchamp told of one adult male woodrat that was trapped over two consecutive nights and the surface distance between the trap sites was several hundred yards.

"He may have covered the distance on the surface placing himself at substantial risk, but it seems more likely that he picked his way through the corridors of a cave, which are found in this area, and are inhabited by woodrats," Duchamp said.

Once found on mountains throughout the state, woodrats - also occasionally called packrats - today are limited to certain rocky stretches of the Allegheny and Appalachian mountains. They're in trouble, and have been for some time. But some populations are at greater risk than others. The Allegheny woodrat has been a state-threatened species since June of 1983.

"Pennsylvania once had a solid woodrat population from Maryland to New York, but development and forest fragmentation have changed that," said Cal Butchkoski, Game Commission small mammals biologist. "They now are extirpated in New York, and also Connecticut. Increases in predators - such as domestic cats and dogs, as well as raccoons and foxes - also have played a role, as have changes in forest composition, and their susceptibility to raccoon roundworm. It's fair to say woodrats have been under siege for a long, long time."

Working under the Game Commission's State Wildlife Grants Program, which was created by and is subsidized by the U.S. Fish and Wildlife Service, the IUP research team, since mid-May, has been working to trap, tag and place telemetry collars on woodrats. The team is comprised of Dr. Duchamp and Dr. Jeff Larkin, assistant professor of conservation biology, and biologists Karen "Jamie" Paul, of Acme, and Mike Shank, of Clune; and graduate student Jennifer Hoffman, of Ventura, California. They work long days, and perform plenty of after-midnight telemetry work, and generally start the work day climbing the mountainside and scampering over the wet, slippery boulders to check box traps, which are rebaited and set every evening before dark and checked at daybreak. Traps are disabled during daytime hours.

Although woodrats are in decline, particularly in Pennsylvania's northern tier and eastern counties, Duchamp reported that he's had little problem catching woodrats on both public and private grounds they have been trapping on Chestnut Ridge.

"We've been going to general areas that have records of active sites - although some records are 15 to 20 years old - and we found woodrats at or near every one of them," Duchamp said. "Some of the populations are very small, which would indicate that there is some amount of dispersal going on between nearby populations. I'm just surprised that we really haven't found an empty site yet, partly because this area is on the northwestern edge of the woodrat's range, and partly because the records we're using are pretty old."

The IUP researchers also will experiment by placing caches of acorns in activity centers in an effort to stimulate a population increase.

"Part of the woodrat decline has been linked to the American chestnut blight and gypsy moth deforestation," Duchamp said. "So we're going to see if supplying acorns to colonized areas that are relatively inaccessible to other wildlife will serve as a means of boosting the productivity and coax the population to grow."

Information about juvenile dispersal among the smaller populations that comprise a woodrat meta-population - a regional woodrat population covering the Alleghenies' Chestnut and Laurel ridges in Indiana and Westmoreland counties - is unclear.

"As we get more collars on young adult animals that disperse, we should learn more about how they are getting from one rock patch to another," Larkin said. "Are there specific corridors that they use? Are they moving underground? Is there overland movement? What's the chance it will be picked off by a predator? These are questions we hope to answer."

Upon completion of the study, IUP expects to deliver information and GIS images focusing on habitat features that may serve as dispersal corridors or barriers; a model for predicting woodrat meta-population viability and current information about the demography of Chestnut Ridge woodrat populations.

Woodrats are capable of dispersing a mile or two. On the Chestnut Ridge, where populations appear to be nowhere near as distressed as those fragmented in other parts of the state, Duchamp said, dispersal probably is a singular event done primarily by younger animals.

"We're hoping to catch them during their big move, so we can record their route, the time it takes and the distance they travel," Duchamp explained. "We'd like to better understand the probability of dispersal.

Butchkoski pointed out that woodrat dispersal in other areas of the Commonwealth takes generations for small movements that often end abruptly when dispersing woodrats encounter barriers or predators.

"Woodrats live on islands of rock," Butchkoski said. "They are tied to geology for denning sites and forest composition for food and cover. If they encounter trouble on one ridge, it becomes next to impossible for the colony to pick up stakes and move to the next ridge.

"It might take a woodrat population 20 to 50 years to shift 20 miles in reasonably good habitat. If the habitat isn't good, the woodrat has to cross a valley, or an interstate highway or suburbia - where there's no cover or food - but plenty of predators. It's like walking the plank."

The Allegheny woodrat, like the opossum, is a living fossil. It has inhabited the rockier sections of the Mid-Atlantic States since the days of the wooly mammoth. Given its habitat preferences, the woodrat had its habitat market cornered for centuries upon centuries; few other creatures prefer to live on boulder-strewn ridges and talus slopes. But now, after thousands of years, this creature's existence is threatened.

"Greater than five percent of the world's breeding population of woodrats is found in Pennsylvania, which means the Commonwealth has a global responsibility to help protect and manage this species, holding onto both the woodrat's retreating northeastern range and the nuclei of healthy populations, including those on Chestnut Ridge," said Calvin W. DuBrock, Game Commission Bureau of Wildlife Management director. "But, big population centers have disappeared since the '70s, including those on the Blue Mountain, from Dauphin County east to the Lehigh River, and a veritable woodrat city near Kennerdell in Franklin County overlooking the Allegheny River. "

With a lifespan that is generally about 18 months, woodrats pretty much grow and go. Males usually have shorter lives - probably related to pitfalls of dispersal. Woodrats are active year-round, primarily vegetarian and seem to peacefully coexist among the rocks with timber rattlesnakes and copperheads. They have two to three litters of young, beginning in April.

For more information, visit the Game Commission’s Allegheny Woodrat webpage.

7/20/2007