Interrelationships among northern flying squirrels, truffles, and microhabitat structure in Sierra Nevada old-growth habitat

During 1997–1998, we investigated the influence of both the relative abundance of truffles, preferred food\ud items, and microhabitat structure on the occurrence of northern flying squirrels (Glaucomys sabrinus Shaw) in old-growth\ud forest habitat of the Sierra Nevada Range, U.S.A. Following live-trapping sessions, we searched the forest floor\ud for truffle diggings and sampled the soil for truffles. Diggings were more abundant where flying squirrels were captured,\ud suggesting squirrels were active near areas of the forest floor where truffles had recently been excavated. The\ud frequency of sampling plots with truffles was higher where squirrels were captured, further suggesting preferences for\ud microhabitats where truffles were more abundant. We also measured 15 microhabitat variables at trap stations to evaluate\ud the influence of aboveground microhabitat characteristics on squirrel occurrence. Results indicated that flying squirrels\ud preferred microhabitats with understory cover, which may minimize predation from aerial predators like spotted\ud owls (Strix occidentalis Merriam). Neither abundance of coarse woody debris, a feature conducive to fungal growth,\ud nor the abundance of potential nesting sites (i.e., snags) measurably influenced squirrel occurrence. While various\ud aboveground forest-microhabitat characteristics affect the use of old-growth forests by flying squirrels, these animals refine\ud their use of these forests based on fine-scale changes in the availability of a highly preferred and ephemeral food item