Microhabitat and Landscape Characteristics Associated with the Threatened Allegheny Woodrat

Abstract

Populations of Allegheny woodrat (Neotoma magister) in the northeastern U.S. have declined recently for unexplained reasons. The species is believed to be separate from the more widely distributed eastern woodrat (Neotoma floridana; Ord 1818) and is listed as threatened in Pennsylvania. Several hypotheses have been proposed for the decline in N. magister, but little information on the ecology of the species is available to direct conservation efforts. Using a multi‐scale approach, we compared recent microhabitat and landscape characteristics among historical, occupied, and reference sites to pre‐1960 versus post‐1985 landscape characteristics associated with historical woodrat sites. Our analysis suggests that habitat characteristics, such as percent rock cover and aspect, have affected the current distribution of woodrats in Pennsylvania. Differences in microhabitat probably do not account for the disappearance of woodrats from historical sites. We found no evidence that low levels of human activity near nest sites or that forest fragmentation were directly responsible for the observed decline. But we observed increases in residential and agricultural cover near historical sites between the 1950s and 1980s and higher percentages of croplands and other agricultural cover at historical sites than at occupied sites. These land uses are capable of supporting high populations of Great Horned Owls (Bubo virginianus) and raccoons (Procyon lotor). Increased predation by Great Horned Owls and exposure to the raccoon roundworm (Baylisascaris procyonis) have been suggested as potential factors contributing to the decline of woodrat populations in the northeastern United States. Historical sites bad significantly higher percentages of coniferous and mixed forest cover than occupied sites, and the percentage of coniferous forest cover at historical sites increased significantly between the 1950s and 1980s. Therefore, we speculate that changes in forest composition in Pennsylvania may have adversely affected habitat quality (particularly food availability) for Allegheny woodrats and contributed to their extirpation from historical sites.

Habitat Use of the Key Largo Woodrat (Neotoma floridana smalli)

“…Occupancy also showed a trend toward higher occupancy along abandoned roads (p=0.12). Contrary to some of the previous research (Olsen 1973;Balcom & Yahner 1996;Gerber et al 2003), no forest metrics were found to be relevant to either the presence or occupancy of a woodrat nest.…”

“…Pilot surveys indicated that the average sighting distance by an observer searching for a nest was 14 m. On all surveys, observers walked along each transect and investigated all potential nest sites visible on either side. Though woodrats are known to build nests using a variety of materials (Goodyear 1985;McCleery 2003;McCleery et al 2006b;Winchester 2007;Winchester et al 2009), they will often use sticks to improve the nest site (Goodyear 1985;Balcom & Yahner 1996). I defined a nest as a feature exhibiting characteristic "stick-stacking", which is especially noticeable when underneath a ledge or other cover, and is easily distinguished from natural litterfall ( Figure 3).…”

“…Although stick-stacking activity is known to be an indicator of recent woodrat presence (Balcom & Yahner 1996), it does not necessarily mean that a nest is currently occupied. To determine if nests found in the survey were occupied, I used 33 Reconyx PC800 remote cameras to detect woodrat activity.…”

“…Woodrats can exhibit strong habitat preferences (Cameron & Rainey 1972;Wright 1973), and have been observed to choose nest sites on the basis of the defensibility of core substrate against predators (e.g., cacti; Brown et al 1972;Smith 1995), surrounding vegetation (e.g., Poison Oak; Gerber et al 2003), over-and understory cover (Olsen 1973;Gerber et al 2003), and variation in tree species assemblages (Balcom & Yahner 1996).…”

“…On the basis of previous studies that report woodrats nesting in trash piles and other anthropogenic substrates (Goodyear 1985;Shaw 1994;McCleery et al 2006;Winchester et al 2009) and the suggestion that woodrats may be limited by nest substrate (Winchester 2007;Winchester et al 2009), I hypothesized that woodrat nests would be more numerous and have higher occupancy rates in areas associated with human disturbance (old roads, paved roads, young forest). I also hypothesized that woodrats would choose sites on the basis of finer-scale forest structure traits that may not be captured in a forest age metric such as canopy cover and foliage density (Olsen 1973;Balcom & Yahner 1996;Gerber et al 2003).…”