Page Two

INTRODUCTION

The Allegheny woodrat's (Neotoma magister) range once stretched from northern Alabama to Connecticut, and west into Kentucky, Indiana, and Tennessee (Poole 1940). Since about 1960, this range has been shrinking. The woodrat has disappeared from Connecticut and New York (Hall 1990), and is threatened in New Jersey, Ohio, Maryland, Indiana, and Pennsylvania (Hall 1990; Genoways and Brenner 1985). The reason for the decline of the Allegheny woodrat is not clear.

A major historical habitat of the woodrat in south central Pennsylvania has been the parallel ridgetops of the eastern Appalachian mountains. This study includes Blue Mountain, Cumberland County PA, and measures availability of the woodrat's favorite habitat, loose sandstone outcroppings. The actual area of available woodrat habitat on Blue Mountain has never been measured. Data from this study could help determine if Blue Mountain should be the focus of future recolonization efforts.

     Once thought to be a subspecies of the eastern woodrat (Neotoma floridana), the Allegheny woodrat was recognized as a distinct species after analysis of woodrat mitochondrial DNA restriction sites (Hayes and Harrison 1992). The second largest member of the native North American rats and mice (family Cricetidae), the woodrat is brownish-grey with a white underside. It has four digits on its front feet and five on its hind feet. It averages between 38 to 46 cm in length, with the tail about 15 to 20 cm of its total body length (Merritt 1987).

     The woodrat prefers limestone caves or rocky habitats (Poole 1940; Doutt et al 1967). It is primarily nocturnal, and prefers to live in solitary dens. Woodrats build caches of berries, fruits, nuts, and vegetation (Mullen 1994). They breed from late winter to late summer, with a gestation of 35 days (Fitch 1956). Females may have two to three litters per year, averaging two young in each litter (Poole 1940). The woodrat seems to live about three yeas in the wild (Merritt 1987). Since the Allegheny woodrat was considered a subspecies of the Eastern woodrat until 1992, data taken earlier than this might refer to either the Eastern woodrat or the Allegheny woodrat. However, the Eastern woodrat and the Allegheny woodrat share similar lifestyles; therefore the same data may apply to both species.

     Many factors have been proposed to explain the decline of the Allegheny woodrat. Acorns have been reported as an important food source for woodrats (Poole 1940). Studies have suggested that gypsy moth (Lymantria dispar L.) defoliation of oaks (Quercus spp.) may be reducing the supply of acorns available to woodrats, seriously affecting the available food source especially in areas where woodrats depend heavily on acorns throughout the winter (Hall 1988). Recent studies indicate that woodrats may cross long distances to collect preferred foods such as acorns, rather than simply foraging near the nest for available food (Wright & Hall 1996). This long distance foraging increases the woodrat's exposure to predators. Great Horned Owl (Bubo virginianus) populations have been reportedly increasing in areas where habitat is adjacent to agricultural fields, and are known predators of Allegheny woodrats (Balcolm & Yahner 1996). The encroachment of cultivated land on woodrat habitat also creates a higher concentration of raccoons (Procyon lotor) (Hoffmann & Gottschang 1977; Sonenshine & Winslow 1972), which can carry a parasite fatal to woodrats (Kazacos 1982). This roundworm (Baylisascaris procyonis) has been suggested as a causitive factor in the extirpation of woodrats from New York (McGowan 1993) and New Jersey (Balcon & Yahner 1996). B. procyonis is known to exist in Pennsylvania (Latchford 1998; Wright 1998), and is present in the raccoon population on Blue Mountain, Cumberland County, PA (Wright 1998). The rate of infection is unknown.

Photo courtesy of Gene Wingert

     Because of present and historical fragmentation of habitat and the woodrats' solitary lifestyle, studies have suggested that N. magister exists as a metapopulation (Balcom & Yahner 1996; Wright 1998). Unlike a continuous population, a metapopulation can be considered to be individuals inhabiting a discontinuous distribution of suitable habitat seperated by unsuitable habitat. Local extinction in any given patch may be common but proximity to another habitat patch increases the liklihood of recolonization (McCullough). This local extinction and recolonization has been observed in woodrat populations (Wright 1996), suggesting that woodrats should be considered in the broader sense of a metapopulation rather than considering the individuals on each rocky outcropping as an isolated population.

     Woodrats have been reported to make several foraging trips a night, with distances between 20-160 meters from their den (Wright 1996). Woodrats may be faithful to one den site for a long period of time, or they may shift dens quite frequently. Permanent den sites have been suggested as a limiting resource, as woodrats tend to live farther than 30 meters from their nearest neighbor (Wright 1996). Woodrats have been reported to travel from 5 meters to nearly 4700 meters during a den shift. The linear distance between den shifts tends to be less than 100 meters with a reported median distance of 40 meters (Corbett & Shinkle 1998).

     This study measures the patch size and distance between patches for suitable Allegheny woodrat habitat on Blue Mountain between the Susquehanna River (N 40 degrees 20 minutes, W 76 degrees 54 minutes) and the elbow (N 40 degrees 16 minutes, W 77 degrees 20 minutes). Mean and median patch size and distance between patches was calculated as well as total available habitat. These data were used to group potential subunit habitat patches in this metapopulation, using 100 meters as a reasonable distance between subunits within a metapopulation. Woodrats can travel longer distances between patches, however as distance to a patch increases the likelihood of woodrats emigrating to that patch decreases. According to the definition, Blue Mountain is one metapopulation, and in the case of total extinction of the metapopulation on Blue Mountain, recolonization from a nearby ridgtop is possible but unlikely.

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