Masters Theses

Date of Award

6-1988

Degree Type

Thesis

Degree Name

Master of Science

Major

Ecology and Evolutionary Biology

Major Professor

Michael R. Pelton

Committee Members

Boyd Dearden, John Gittleman, Arthur Echternacht

Abstract

Examination of 170 gray fox (Urocyon cinereoargenteus) scats collected between Sept. 1986 and Aug. 1987 on the Oak Ridge Reservation (ORR), east Tennessee, revealed that plant foods were utilized most heavily, followed by invertebrate and animal prey. Proportions of the 3 categories utilized were not evenly distributed among months and were dictated by availability. Biological seasons were delineated by detection of statistically significant shifts in diet among the 3 food categories. Animal prey, predominantly rabbits and rodents, comprised 67.0% of winter (Jan.-Apr.) dry weight (100% occurrence); arthropods, predominantly 17-year locusts (Maoicicada sp.), comprised 96.1% of spring (May) dry weight (275% occurrence); plant material, predominantly persimmon, cherry, blackberry and squaw-root, comprised 92.9% of summerfall (June-Dec.) dry weight (161.6% occurrence). This study indicated that gray foxes may switch dietary trophic level depending on seasonal food availability.

Home range sizes of gray foxes were determined from radio-telemetry data (Sept. 1986-Aug. 1987) at the ORR, East Tennessee. Minimum density was estimated at 0.45 adult gray foxes per km2. Average composite home range size was 3.97 km sup>2 for 10 gray foxes, (4.41 km sup>2 for adults (n=6) and 3.32 km sup>2 for subadults (n=4)). No significant differences were detected among home range sizes between males and females or between adult and subadult foxes. Seasonal home range sizes were tested for differences based on seasons of high (spring-fall: insect and fruit prey) or low (winter: animal prey) food availability and breeding-cycle (breeding, pup-rearing and prebreeding). Statistical analysis detected no significant differences among seasons, probably due to high variability between individual foxes. Changes in home range size among seasons for individual foxes did not correspond to any obvious pattern or environmental influence. Territoriality and monogamy were suggested by closely coinciding home ranges of adult male and female pairs, with little overlap between adult males or adult females. Extensive overlap of home ranges by subadult foxes (female, in this case) with one adult male fox indicated that family aggregations may occupy the same home range. Despite seasonally differential area-utilization, boundaries for composite home ranges seemed to be recognized by neighboring foxes year-round; "core areas" within home ranges remained relatively constant. Territoriality may be advantageous where periods of food scarcity (e.g. winter) occur. It is suggested that territory sizes are adjusted to contain a sufficient year-round food supply. All statements regarding the relationship between resource dispersion, home range size or territoriality are tentative, however, due to high variation among individuals and small sample size. Gray fox activity patterns and habitat use also were determined from radio-telemetry data. Foxes were generally active nocturnally (66.6% active), inactive diurnally (21.9% active), and less active during early morning (26.6% active) than evening (54.3% active). Chi-square tests were used to compare activity patterns for 4 different sets of months ("seasons") based on food-type exploitation, relative food abundance, breeding cycle and degree of vegetative (foliage) cover. The most highly significant difference was detected between months of vi high vegetative cover (May-Oct.), when early morning and daylight activity levels were higher, and months of low (Nov.-Apr.) vegetative cover.

A prey base study indicated (although not statistically significant) that winter small mammal populations were most abundant in mature pine habitat, followed by oldfield, deciduous forest, and young pine habitat, respectively; variation in trapping success among seasons and replicate grids, however, was high. Habitat utilization analysis showed that annually, foxes selected young pine more than expected relative to availability. Seasonal analysis based on food-type exploitation revealed that nocturnally, all habitat types were used in proportion to availability in winter and spring. In summer-fall young pine was used significantly more than expected; this may have been due to high concentrations of blackberries (which ripen in summer) within this habitat type. A slightly higher selection of mature pine was observed in winter, and might be attributed to a higher concentration of small mammals (a winter food source) within this habitat type. High daytime use of young pine habitat persisted year-round. Observed daytime resting sites were in thick early-successional vegetation, rocky ledges or underground holes. Maternal dens were dug into the roots of windthrown trees.

Hence, while changes in seasonal prey dispersion (animal, insect, and fruit prey) may not influence seasonal home range sizes, shifts in habitat use within a constant territory may occur according to location of seasonally available foods.

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