Electronic Field Guide » Featured Wildlife Species » Allegheny Woodrat
Protecting and Creating Allegheny Woodrat Habitat during Natural Gas Exploration and Development
Prepared by Kevin Yoder and Margaret Brittingham (Ecosystem Science and Management)
|The Allegheny Woodrat is a rare, shy species currently listed as threatened in Pennsylvania (Aura Stauffer)|
The historic Allegheny woodrat range stretchedfrom southern New York, western Connecticut, and northern New Jersey south through much of Pennsylvania, western Maryland, Virginia, North Carolina, and southern Ohio and Indiana. There are several different species of woodrats in the United States, but the Allegheny woodrat is the only one found in Pennsylvania.
Allegheny woodrats were once very common in the mountains of Pennsylvania, but populations have been declining, and woodrats are now extirpated from much of their historic range. Today, local populations still exist in southwest, southcentral, and northcentral portions of the state. Some of Pennsylvania’s woodrat populations are found along the ridgetops of the Ridge and Valley province. This region does not overlie the Marcellus shale. However, Allegheny woodrat populations also exist on the Appalachian Plateau in southwest Pennsylvania and in portions of Centre, Clinton, Lycoming, and Tioga Counties, where natural gas development is underway. Natural gas development near Allegheny woodrat habitat can reduce the habitat quantity and quality if precautions are not taken during the planning process.
|Rock outcrops provide woodrats with cover and den sites (Cal Butchkowski)|
Life History and Ecology
Allegheny woodrats have brown-gray fur with a white underside and a long, bicolored and fur-covered tail. At first glance the Allegheny woodrat may seem physically similar in appearance to the exotic Norway and black rats (Rattus spp.), as well as the eastern woodrat (Neotoma floridana). Allegheny woodrats can be distinguished from Norway rats by their blunt nose, long whiskers, big ears, and furry tail.
Allegheny woodrats are generally solitary, actively defend their territories, and tolerate other woodrats only during the breeding season. Though communities of woodrats may exist in suitable habitat, subpopulations are very small, with only 1–5 individuals per rock site.
Allegheny woodrats have lower reproductive potential than other rodents. The average litter size is 2–3 pups, and some females possibly produce two, even three litters between mid-March and early September.
The timing of the breeding season varies with location. In southeastern Pennsylvania, births occurred between mid-March and October. Breeding in Virginia occurred year-round, with most young being born between May and October.
Allegheny woodrats are packrats and build nests deep within rock outcrops, crevices, fissures, or caves. Nest materials include shredded bark and grasses. Debris piles of sticks, bark, bones, feathers, feces, and trash may be built to protect the openings of caves or fissures.
A rather unique behavior of woodrats is the pattern of defecating repeatedly in the same location. These are known as latrine areas. They are apparently used over several years by multiple individuals and can become 8–10 inches wide. This unusual behavior can be helpful in determining the current or historical presence of woodrats. These nocturnal animals are not commonly observed, so biologists rely on woodrat sign such as latrine sites to detect woodrats.
Allegheny woodrats are often found in small and isolated clusters.The clusters are interconnected through the movement and dispersal of individual woodrats. Dispersal ensures gene flow between clusters, so maintaining the habitat linkage between them is important. Empty den sites also play an important role in facilitating the movement of woodrats. Allegheny woodrats will recolonize these empty habitats and may eventually start a new population. Habitat fragmentationby human development may block dispersal routes, making the recolonization of historic sites less frequent and less likely.
|Acorns are an important high-energy food for woodrats (M. Brittingham)|
Soft mast plays an important role as a food source during the spring and summer months, and serves as a buffer against hard mast failures. Blackberry (Rubus allegheniensis), leaves, ferns, holly (Ilex spp.), blueberry (Vaccinium spp.) fruit, and lichens are also consumed year-round.
Fungi account for about 10 percent of a typical woodrat’s diet on the Allegheny plateau in all seasons. Fungi such as mushrooms are used because they are nutritious and dry and cache well.
Like many small mammals, most of the Allegheny woodrat’s activity occurs under the cover of darkness. They tend to stay close to den sites, but will forage at night to gather and store food. The extent of woodrat movement changes seasonally. Allegheny woodrats have larger (10–12 acres) home ranges during the summer as they forage fairly widely in search of food. During the fall and winter, woodrats rely on cached food and have smaller (1–2.5 acres) home ranges. Woodrats may change den locations during the summer, but use only one den after midautumn.
Most woodrats exhibit a high site fidelity and low dispersal rates. Long dispersals are unlikely, but occur often enough to recolonize vacant habitats. When woodrats do choose to disperse, they are capable of traveling about 2 miles. Dispersing woodrats tend to move along rock outcrops arranged in a linear pattern. For this reason, it is important not to fragment these habitats. Roads, pipelines, and other forms of natural gas-related infrastructure may become barriers to woodrat movements and dispersal.
Reasons for Decline
Many researchers hypothesize that four different factors contribute to the population decline of Allegheny woodrats. The suggested causes are:
· Increased changes in the landscape, such as forest fragmentation and changing forest composition.
· Reduced availability of acorns and American chestnuts (Castanea dentata).
· Predation by great horned owls (Bubo virginianus).
· Infection and subsequent mortality from a nematode parasite, Baylisascaris procyonis, carried by raccoons (Procyon lotor).
Natural gas development within the Allegheny woodrat range has the potential to increase all four of these factors to some degree.
As a natural gas field develops, it requires the construction of new infrastructure to extract and move the gas. This means that new roads, pipelines, well pads, and compressor stations will need to be created throughout the Marcellus region. Installation of this infrastructure will lead to direct forest loss as well as the dissection and fragmentation of woodrat habitat. Connectivity between woodrat dens is important for the survival of an Allegheny woodrat population. Roads and pipelines that are created between Allegheny woodrat dens may hinder woodrat dispersal and movement between dens.
Allegheny woodrats depend heavily on hard mast as a high-energy food source throughout the year. The American chestnut was likely a primary food source for the Allegheny woodrat before it was virtually eliminated from the landscape by an exotic fungus (Cryphonectria parasitica). Today, woodrats rely on acorns from oak trees as a source of hard mast. Natural gas development requires the clearing of mast-producing trees that provide food for woodrats and many other wildlife species. Roads and pipelines may also create barriers between den sites and oak stands, separating woodrats from their food source.
One of the Allegheny woodrat’s most significant predators is the great horned owl. Great horned owls are habitat generalists that tend to be associated with fragmented landscapes. Owls use openings created within forested landscapes as hunting areas. If natural gas development leads to the creation of multiple forest openings, it may result in an increase in great horned owl populations and Allegheny woodrat predation. Other predators that thrive in fragmented habitats and prey on woodrats include snakes, feral cats, bobcats and foxes
The final threat from natural gas development is that it will lead to more of the landscape being accessible to raccoons. Pipelines and other linear features may serve as travel corridors for raccoons. Predators such as raccoons often travel along rights-of-way because of ease of travel. Raccoons may travel along pipelines and roads deeper into forests, leading to the spread of the parasitic nematode Baylisascaris procyonis. Because woodrats are packrats and are continually collecting items to take back to their dens, they may act as an intermediate host for B. procyonis by ingesting the nematode eggs while collecting dried raccoon feces. Infection leads to lethargy, loss of muscle control, and eventual death.
The extent to which natural gas development affects Allegheny woodrat populations will depend on the identification and protection of woodrat habitat. The simplest way to protect Allegheny woodrat habitat is to enforce a no-disturbance buffer around rocky habitats or known woodrat den sites. With horizontal drilling, natural gas can still be safely extracted from underneath the den sites without disturbing the area.
The best way to sustainably extract natural gas in Allegheny woodrat habitat is to protect woodrat den sites and the forest surrounding them. Existing habitat sites and short (< 1 mile) dispersal corridors require protection from permanent forest fragmentation and dissection. This means that no or very little surface activity should be allowed within about 1 mile of a den site. In addition, potential Allegheny woodrat habitat near active colonies should be protectedso that dispersing woodrats can reach and occupy the vacant sites. Potential habitat includes rock outcrops, cliffs, ledges, boulder fields, and caves, especially when found on southeast and southwest slopes. Natural gas located underneath these buffers can be extracted by drilling horizontally from pads located on the periphery of the buffer zone.
Though limited, there are some reclamation options that can help to provide protective cover for woodrats. Rocks that are unearthed during the construction of pipelines can be placed in piles along the edges of the pipeline to provide additional cover for woodrats or other small animals moving along the pipeline. The creation of denning habitat which would include sub-surface rocks is only recommended within the forest interior at least 1 mile from any pipeline or road.
Deciduous, mast-producing trees provide important food sources for Allegheny woodrats and should be planted by these sites. In the near future hybrid chestnut seedlings will be available for use in restoration. For more information and availability, see the American Chestnut Foundation website (http://www.acf.org/). Soft-mast species associated with early successional habitats, such as greenbrier (Smilax spp.) and blackberry, are also important food sources that can be planted during reclamation.
Pennsylvania Natural Diversity Inventory (PNDI) Review
Disturbance to woodrats and their habitats can be avoided by careful planning in the early stages of a proposed Marcellus project. During this period, representatives for the gas company can check the PNDI database (http://www.gis.dcnr.state.pa.us/hgis-er/Login.aspx) to determine if there are woodrats within a project area. The PNDI database contains the known locations for threatened and endangered (T&E) species in Pennsylvania that have been mapped by scientists over many years. This database is continually being updated with new information. For more information on this environmental review tool, see the Pennsylvania Natural Heritage Program website (http://www.naturalheritage.state.pa.us).
If woodrats or other T&E species potentially occur within the proposed development, the PNDI database will produce a receipt telling the applicant which regulatory agency or agencies should be contacted. The PA Game Commission is the regulatory agency for woodrats and other mammals and bird species. The applicant should then contact the PGC using the information provided. The PGC reviewer will help provide information on which steps, if any, need to be taken to avoid affecting woodrats or other T&E species under their jurisdiction.
Not all woodrat populations in the state are known or mapped. Even if the PNDI review shows that there is no impact, a landowner may want to have the gas company hire a qualified consultant to do a habitat evaluation for woodrats, especially if rocky habitat is known to occur in the proposed project area. If it is determined that woodrats do occur on the property, follow the recommendations above to protect and enhance habitat for this rare Pennsylvania native.
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