Third and fourth order habitat selection of North American porcupines (Erethizon dorsatum) differs in winter and non-winter seasons

Background/Question/Methods

Habitat selection, the use of resources by organisms disproportionate to the availability of those resources, has been studied at four different scales: geographic range, home range, general features of a region (i.e. habitats), and particular elements of a region (i.e. food items).  Each scale can reveal different selection preferences.  Previous work has shown that researchers need to examine selection using at least two scales.  The purpose of this experiment was to 1) determine if the North American porcupine selected habitat differently at two scales, general features of a region and particular elements of a region and 2) determine if habitat selection differed in winter and non-winter seasons. A population in Canton, NY was studied from September 2009-April 2010.  A 40 hectare section of forest was sampled using the point-quarter method to assess four habitat characteristics: tree species composition, diameter at breast height, tree height, and canopy width. Individuals were radiotracked and their locations recorded with GPS.  At each location, a modified point-quarter survey was used to evaluate the four closest trees and the porcupine selected tree for the same four habitat characteristics.  For each tree species, importance values, a measure of a species’ relative dominance in a community, were calculated.

Results/Conclusions

Porcupines were tracked 88 times (winter: n = 40, non-winter: n =48) with 26 distinct locations, 6 locations being used for both seasons.  Some trees were used multiple times by porcupines.  At the general features scale of selection without distinguishing season, porcupines selected stands that included hemlock, basswood, and black ash.  At the particular elements scale of selection without distinguishing season, porcupines selected hemlocks and red maples. This research supports previous conclusions that habitat selection should be studied using two scales of selection because the species selected for general features are different from the species selected at the particular elements scale. When the data is separated into winter and non-winter seasons, the selection at each scale changes slightly.  At the general habitat scale in winter, porcupines prefer hemlock stands while in non-winter, a mix of basswood and hemlock are preferred.  At the particular features scale in winter, porcupines prefer hemlock, basswood, oak, and white pine; and in non-winter they prefer basswood and white pine.  This research shows that when the data is separated by season, new trends in selection preferences emerge.  This work emphasizes the importance of including not only spatial, but also temporal factors when determining habitat selection.