Habitat Characteristics and Revised Gap Landscape Analysis for the Northern Flying Squirrel (Glaucomys Sabrinus), a State Endangered Species in Pennsylvania

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We quantified the habitat characteristics associated with capture sites (2003-2006) of the state endangered northern flying squirrel (Glaucomys sabrinus) in Pennsylvania to develop management recommendations that help ensure its continued persistence in the Appalachians. In addition, we used this refined understanding of northern flying squirrel habitat to update the Pennsylvania Gap analysis model for this species. We examined habitat at both the landscape and local level and determined that northern flying squirrels preferred sites that contained mature (>95 y old) mixed coniferous forests and were adjacent to a permanent water source. In addition, sites where northern flying squirrels were captured contained significantly more overstory trees (all species), saplings and rock cover. After using these data to refine the Pennsylvania Gap model for northern flying squirrels, we reduced the primary or core habitat predicted for this species in the state by 90%. Our findings further support the reliance of this species on specialized habitat in the Appalachians and help reinforce the need to conserve and manage mature mixed-coniferous forest stands, which are threatened by exotic pests and human development throughout the region.


The northern flying squirrel ( Glaucomys sabrinus) , a highly specialized arboreal sciurid, is dependent upon mature forests with a significant conifer component (Wells-Gosling and Heaney, 1984; Weigl et al., 1999; Loeb et al., 2000; Weigl, 2007). In Pennsylvania, red spruce (Picea rubens) , balsam fir (Abies bakamea) and eastern hemlock ( Tsuga canadensis) are critical elements of northern flying squirrel habitat. Mature forest stands allow efficient locomotion via gliding, suitable numbers of nest cavities and the regular production of important dietary items including hypogeous fungi and arboreal lichens (Weigl et al, 1999; Loeb et al, 2000) . As a habitat specialist, the northern flying squirrel is highly susceptible to habitat loss and degradation (Mahan et al., 1999; Ford et al, 2004). As an example, a subspecies of northern flying squirrel found south of Pennsylvania (G. s. coloratus) consists of several small, disjunct populations and was listed in 1971 under the Federal Endangered Species Act (Weigl et al, 1999; Weigl, 2007).

Northern flying squirrels in Pennsylvania were historically found across the northern portion of the state south through the Appalachians into West Virginia (Merritt, 1987; Mahan et al, 1999). In addition, northern flying squirrel populations in Pennsylvania were once contiguous with more northerly populations in New York and represented the southern edge of the range of the subspecies, G. s. macrotis. Recent live-trapping and nestbox surveys performed throughout Pennsylvania since 1990, however, have located northern flying squirrels from only a limited area in the northeast portion of the state and in one eastern hemlock stand in northwestern Pennsylvania, suggesting the species' range has contracted and become significantly more disjunct from both northern and southern populations (Mahan et al., 1999; Steele et al., 2004). Due to this apparent reduction in range and the perception of a drop in population size, the species was listed as endangered by the Pennsylvania Game Commission in Nov. 2007.

The range reduction and population decline of northern flying squirrels in Pennsylvania may be attributed to several factors, including the loss of old-growth and mature forest habitat, destruction and fragmentation of remaining suitable habitat from anthropogenic causes, competition from the southern flying squirrel ( Glaucomys volans) , and the possibility of a debilitating parasite transmitted by the southern flying squirrel (Weigl et al., 1999; Weigl, 2007; Krichbaum et al., 2010). Furthermore, eastern hemlock forests, a critical component of northern flying squirrel habitat in Pennsylvania, have an uncertain future in the state. …