Wildlife News
PA Northern Flying Squirrels in Trouble
By TSN
Oct 20, 2004, 1:53pm

HARRISBURG, PA - Ongoing field research funded by the Pennsylvania Game Commission and U.S. Fish and Wildlife Service has uncovered that the state's northern flying squirrels are uncharacteristically sharing habitat - even nesting quarters - with their look-alike cousin, the southern flying squirrel. That may mean trouble for northerns, which already are in short supply in Pennsylvania and further threatened by the European wooly adelgid, an insect that has been devouring the state's hemlock tree stands, the preferred habitat of northerns.

The big problem with northerns and southerns sharing habitat and living quarters, according to the fieldwork - a State Wildlife Grants Program (SWG) project - is a parasite called Strongyloides robustus that is carried by southerns and can be lethal to northerns. The parasite poses no threat to the southern, but it seems to suppress the northern's ability to put on winter fat, and to even maintain its existing weight.

Pennsylvania's northern tier has always served as sort of a point of demarcation for the southern range of the northern flying squirrel, although there are two subspecies of northerns found south of Pennsylvania. Both subspecies are extremely rare and have been classified as endangered species since the 1970s. Southern flying squirrels are found throughout the eastern United States. Habitat preference and lifestyle differences have helped to naturally keep the species separated for some time. But the southern flying squirrel population is booming in Pennsylvania and elsewhere. The state's northern population, conversely, is known to occur in only two sites: a large population center in Carbon and Monroe counties, and another where a northern turned up recently in Warren County.

"Southern flying squirrels are Pennsylvania's most abundant squirrel; their numbers even exceed the gray squirrel's," noted Cal DuBrock, Game Commission Bureau of Wildlife Management director. "They live in almost every block of forest in the state and at high densities. It's not hard to understand why there appears to be more contact between northerns and southerns, given the way southerns have saturated the state. But given the documented inability of these species to maintain a friendly coexistence, it is somewhat surprising to see the them sharing living quarters and habitat."

Northern flying squirrels, which are slightly larger than southerns, have been sort of an enigmatic species to biologists for decades. Their presence in the state has been recognized for some time. But given their extremely limited distribution and nocturnal lifestyle, it's not hard to understand why northern flying squirrels haven't garnered much attention over the years from wildlife managers, outdoors writers or those who frequent the state's northern woods.

"It's probably fair to say that to virtually all people, a flying squirrel is a flying squirrel," said DuBrock. "But the Game Commission has been aware of the northern flying squirrel's presence as a distinct species in the Commonwealth since as early as 1930, when it was documented in Potter, Greene and Sullivan counties.

"Funding has always limited the Game Commission's ability to intensify its management of nongame species like the northern flying squirrel. But financial support provided by the U.S. Fish and Wildlife Service through its SWG Program has created a means for us to chart the northern flying squirrel's range and status in Pennsylvania. It's overdue and important research that's finally getting the funding our traditional revenue sources - primarily license fees and timber sales - couldn't provide."

The U.S. Congress in 2001 created the SWG Program to support the conservation and recovery of declining fish and wildlife species at the state level. With more than 1,000 animals and plants already listed as federally threatened or endangered, Congress recognized that SWGs are one of the best hopes for reversing fish and wildlife declines. Investing federal dollars at the state level - before a species declines to the point of being federally endangered - was determined to be far more effective than waiting until the populations need expensive "emergency room care" through the Endangered Species Act.

"The SWG Program already is improving the management of America's and Pennsylvania's wildlife resources by injecting otherwise unattainable funding into critically important and starving conservation programs," noted DuBrock. "It has truly helped to expand, refine and strengthen Pennsylvania's fish and wildlife management."

For some time now, the Game Commission staff biologists and members of the Pennsylvania Biological Survey's Mammal Technical Committee have contemplated the possibility of listing the northern flying squirrel as an endangered or threatened species. Dr. Michael Steele of Wilkes University, Dr. Carolyn Mahan of Penn State University's Altoona campus; and Greg Turner, formerly a Wilkes University researcher and now a Game Commission endangered species biologist, all recommended elevating the status of the northern flying squirrel from its current designation as a "protected mammal" to a threatened or an endangered species in their SWG Program-funded research paper, titled A Manual for Long-Term Monitoring and Management of the Threatened Northern Flying Squirrel in Pennsylvania.

"We are discovering that the northern flying squirrel appears to be far more limited in its range in Pennsylvania than previously expected," the researchers reported. "Despite intensive trap efforts and extensive box surveys that have spanned more than two and a half years, we have only been able to locate approximately 17 individuals. Thus it follows that the species is in need of significant protection and further monitoring to formally evaluate the potential threats to the animal. The species distribution is further jeopardized by the current threats to hemlock forests caused by hemlock wooly adelgid, a non-native insect that causes mortality of eastern hemlock trees."

As a direct result of the SWG northern flying squirrel fieldwork, the PBS's Mammal Technical Committee has asked the Game Commission to consider listing northerns as an endangered species, a two-step action that would need to be taken up by the agency's Board of Game Commissioners. The Game Commission's Bureau of Wildlife Management has asked consequently for more information and additional fieldwork to qualify the recommendation.

"One of the benefits of being proactive with declining or rare species is that it allows managers a little more time to better understand the species - as well as the extent of its problems - and make informed decisions," explained Turner. "In coming months, the research team and agency biologists plan to look deeper into the northern's status in Warren County - uncovered in May - and to probe some of the northern's historic haunts in the Honesdale area and at Promised Land State Park."

Fieldwork for the northern flying squirrel project began in January 2002 and continues. Slightly more than $90,000 (75 percent provided by the USFWS) has been dedicated to this research and the team to date has shed considerable light on this reclusive species. Next to the state-endangered Delmarva fox squirrel, northern flying squirrels are Pennsylvania's hardest-to-find tree rodent. When compared to the thriving southern flying squirrel, which has experienced significant population gains and range expansion in recent years, the northern flying squirrel remains a veritable unknown native that continues to isolate itself from researchers and wildlife managers by holing-up in the relative obscurity provided by older stands of spruce and hemlocks in remote areas.

"Right now, the principal way we keep tabs on northern flying squirrels is to set baited live-traps for them or check nesting boxes in cold weather," Turner said. "Once captured, we fit them with electronic radio transmitters. We will be out this fall and winter monitoring squirrels we capture in traps and checking the 550 nesting boxes we've placed during this project. We also intend to construct and install new nest boxes to expand our ongoing statewide survey."

Of course, some of the biggest news to be reported in this SWG project has been uncovering that northern and southern flying squirrels are sharing habitats and living quarters. In most places where the ranges of these squirrels overlap, the arrangement is less than cordial, and southerns often are actively aggressive toward the larger northerns, frequently displacing them from established habitat. The only other places in North America where southern and northern flying squirrels are known to tolerate one another is Michigan's Upper Peninsula and in the higher elevations of the Appalachian Mountains in West Virginia.

These squirrels typically don't share habitats because their habitat preferences are different, as are their wintering arrangements. Southerns prefer deciduous forests with seed- and mast-producing trees, and store foods to carry them through periods of inactivity during winter's cold snaps and deep snows. Northerns are on the move year-round and prefer stands of evergreen. They consume mast and seeds, too, but also will eat lichens and truffle-like fungi. The species is believed to prefer spruce and hemlock stands with a nearby water source, because the trees generally are found in wet areas and the fungi northerns prefer are commonly found accompanying conifer root systems.

Since the SWG researchers have found northerns and southerns sharing habitats and nesting sites, they have been investigating the possibility that southerns may be passing on the Strongyloides robustus parasite to northerns, and ultimately reducing or eliminating their presence in their few remaining Pennsylvania strongholds. It's an occurrence that also has been reported anecdotally by biologists in Michigan and Ontario.

"The occurrence of these two species appears to extend well beyond sympatric use of common habitat," the researchers wrote in their SWG report. "Our observations that the two species can share the same nest (during the non-breeding season), further underscore the likelihood of transmission of a potentially hazardous parasite."

Turner reported he already has found a northern that harbored Strongyloides robustus in study nesting box. In addition, another northern in the study has tested positive for the parasite.

"Fecal samples have revealed northern flying squirrels in Pennsylvania have contracted the parasite," Turner said. "We will continue to collect fecal samples from all captured northerns to monitor and shed further light on this occurrence. But it's important to remember this is a problem of a natural order caused by a flourishing species and suffered by another on the edge of its peripheral range."

The habitat preferences of the northern flying squirrel also subject it to additional harmful pressures, because hemlock stands are currently being preyed upon by wooly adelgids, a European insect that strips and frequently kills hemlock trees. It has devastated and continues to ravage huge chunks of hemlock forestland throughout eastern Pennsylvania.

"It's still unclear how the wooly adelgid ultimately will impact northern flying squirrels, but they do represent a significant threat to the species and other wildlife dependent on these ecosystems," Turner explained. "Right now, they continue to infest the Commonwealth's woodlands. As long as they remain active in our forests, their threat remains genuine."

The flying squirrel does not fly; it is a glider. Using fur-covered membrane that runs from the just above the paw on the front leg to the ankle on the rear leg on each side, the squirrel will jump from a tree and glide downward to a lower location. Flying squirrels use their tail and legs to maneuver while in flight. Unless aided by the wind, squirrels cannot glide upward.