Tassel-Eared Squirrel Population, Habitat Condition, and Dietary Relationships in North-Central Arizona

Abstract

We examined the seasonal population dynamic of tassel-eared squirrels (Sciurus aberti) in north-central Arizona, USA, during 1996-1997 to assess relationships with forest structural habitat condition and dietary fungi use. Our 8 study sites averaged 66 ha and exhibited considerable variation in ponderosa pine (Pinus ponderosa) habitat structure. We conducted capture-recapture trapping during 3 seasons each year, for a total of 56,016 trap days and 2,542 captures of 450 squirrels. We attained population estimates with mean standard error ±10%. Density across periods ranged from 0.05 to 1.03 squirrels/ha, and fluctuated widely, at half our study sites, particularly between April and August trapping periods. Indices of recruitment averaged 0.14 juveniles/female. Survival rates averaged 0.78, with winter survival (0.63) significantly lower than other periods. We analyzed 382 fetal samples for seasonal hypogeous and epigeous fungi, of which 21 taxa were detected. Mean fecal fungal content was significantly higher in August (70.8% relative frequency) than in January (28.2%) and April (9.4%). Recruitment was strongly and positively related to both the number of interlocking canopy trees and August fungal content in fecal samples. August fecal fungal content was positively related to basal area for all tree species. Across all periods, squirrel density was positively related to fecal fungal diversity. Winter squirrel survival was inversely related to snow cover duration and positively related to dietary fungal diversity. Squirrel density fluctuations between April and August were positively tied to pine quadratic mean diameter. Forest management and restoration practices emphasizing intensive, widespread thinning may adversely impact tassel-eared squirrels and the fungi that provide food. Integrating squirrel habitat needs of interlocking canopies and other structural attributes in forest management will benefit squirrel populations.