Characteristics of northern flying squirrel and Townsend's chipmunk populations in second- and old-growth forests

The forested landscape in western Oregon has become increasinglydominated by young, second-growth forests (i.e., those regeneratedafter clear-cutting of previously uncut forests) as a result ofintensive and extensive timber harvesting. There have been fewinvestigations on how wildlife populations respond to these forests.This study compared population characteristics and habitatrelationships of 2 sciurids between second- and old-growth Douglas-firforests.
An important parameter in the characteristics of wildlifepopulations is abundance, but estimation of abundance is a problem foranimals that are not easily captured. I applied various estimators(enumeration, jackknife, moment methods) to data from northern flyingsquirrel (Glaucomvs sabrinus) populations that had low, heterogeneouscapture probabilities (X 0.10) and low densities (.4 animals/ha).
The enumeration method (i.e., the number of individuals captured) wouldhave performed poorly because capture probabilities appeared to varyspatially and temporally. The jackknife estimator-selection procedurewas sensitive to small changes with the data, and estimates did notstabilize with time. Similarly, the moment estimator performed poorlywhen there were and Townsend's chipmunks (Eutamius townsendii) in second- and old-growth
forests.
Flying squirrels are one of the major prey species of the spottedowl (Strix occidentalis), a species that is listed as threatened underthe Endangered Species Act. Estimated densities ranged from 1.1 - 3.3squirrels/ha, and averaged 2.0 and 2.3 in second- and old-growth
stands, respectively. Body mass and survivorship were also similarbetween stand-age class; however, there was a higher proportion offemales in second-growth stands. The findings of similar densities offlying squirrels in these stand types are contrary to expected patternsof abundance and suggests that spotted owls select old-growth forestsfor reasons other than flying squirrel abundance. Flying squirreldensities were not correlated to the measured habitat variables, andmodels relating habitat characteristics at a particular trap stationfailed to predict squirrel occurrence.
Townsend's chipmunks comprise a major proportion of small-mammalbiomass in the central Oregon Cascades, and therefore may beecologically important. I examined differences of Townsend's chipmunkpopulations in second- and old-growth forests. Densities ranged from0.4 to 10.3 chipmunks/ha, and averaged 2.6 and 5.2/ha in second- andold-growth stands, respectively. Chipmunk densities were positivelycorrelated with density of large hard-snags, although this relationshipwas only true in old-growth stands. Chipmunks had smaller home ranges,a greater proportion of females, and a greater proportion of animalsbelieved young-of-the-year in old- than in second-growth stands. Basedon these differences, old-growth stands appeared to provide betterhabitat for Townsend's chipmunks than second-growth stands.