Gerald E. Svendsen

Patterns of scent-mounding in a population of beaver (Castor canadensis)

The frequency and pattern of distribution of scent-mound construction were studied in a population of beaver in southeast Ohio from 1975 through 1977. The study addressed the questions of whether or not the frequency of scent-mound construction varied with season, site, year, and degree of contact with other family groups, and whether the pattern of scent-mounding activity was parsimonious with the idea of “territorial marking.” The number of scent-mounds constructed was determined weekly for each site throughout the ice-free season. Scent-mounding activity was highest in spring and declined and remained low during summer and fall. Significant differences were found amoung sites and over years. Contact with other resident family groups altered both frequency and pattern of scent-mound construction. Scent-mounds did not conform to a “scent-fence” model. The most parsimonious interpretation of function of odor cues deposited on scent-mounds is the effect on the motivational state of residents and nonresidents, increasing the confidence and reducing anxiety in residents smelling their own scent-mound and decreasing the confidence and increasing the readiness to flee in trespassers encountering a strange scent-mound.

Population Parameters and Colony Composition of Beaver (Castor canadensis) in Southeast Ohio

The population dynamics of beaver was studied in SE Ohio from 1974 to 1978. All members of a local population were marked. Family units were a closed social system consisting of a monogamous adult pair, yearlings and kits. Two-year-old beaver dispersed from their natal site in the spring of their third summer of life. The average family unit size prior to dispersal was 5.85, between dispersal and birth of kits was 4.09, and after the birth of kits 6.04. Average annual litter size was 2.7. Litter size varied among years but not among family units. Outbreeding was the rule, only one parentprogeny pair bond formed after the over-winter loss of the adult male. This pair bond lasted only one breeding season, however. Members of each family unit remained together throughout the year and all members, including the adult male, participated in care of the kits.

Territoriality and Behavior in a Population of Pikas (Ochotona princeps)

Pikas ( Ochotona princeps ) were studied on three talus slopes during the summers of 1974 and 1975 in the vicinity of the Rocky Mountain Biological Laboratory, 2,900 m, Gunnison Co., Colorado. The pattern of social organization among marked resident adults was one where males and females maintained territories, which excluded other residents of the same sex but overlapped considerably with residents of the opposite sex forming a pair-wise distribution. Dominance relationships were dependent upon age, residency, and sex; resident adults always expelled intruders of the same sex but were never observed to be dominant outside their territories. Aggressive behavior, exhibited by chases and fights, was the predominant factor in maintenance of territories. Scent-marking and vocalizations occurred in a variety of circumstances and scent-marks did not deter intrusion of invading pikas. Vocalization and olfaction are proposed as means to modify aggressive behavior through sexual and individual recognition.

Castor sacs and anal glands of the north american beaver (Castor canadensis): their histology, development, and relationship to scent communication

Both sexes of beavers possess a pair of castor sacs and a pair of anal glands located in paired subcutaneous cavities between the pelvis and the base of the tail. The castor sacs are not glandular in the histological sense, hence references to these structures as preputial glands or castor glands are misnomers. The wall of the castor sacs is plicate and comprised of three distinct zones: an outer layer of vascular connective tissue, a two-to five-cell-thick layer of mitotic epithelial cells, and several densely packed layers of cornified epithelium which grade into more widely separated sheets toward the lumen. Monocultures of a gram-positive facultatively anaerobic bacterium were present in the lumen of all castor sac preparations. Differences in the frequency of castoreum deposition were not attributable to differences in the structure of the castor sacs. The anal glands of beavers are holocrine sebaceous glands. These glands develop more rapidly than the castor sacs. Anal gland tissue from embryos exhibited cellular characteristics associated with the production of sebum. Secretory activity was evident in all preparations. The relationship of castoreum and anal gland secretion to scent communication among beavers is discussed.

Effects of Climate on the Circannual Rhythm of the Eastern Chipmunk, Tamias striatus

The eastern chipmunk ( Tamias striatus ), a temperate sciurid, has evolved precise timing of breeding in southeast Ohio similar to the strategy found in the Arctic ground squirrel ( Spermophilus undulatus ). Abnormally low ambient temperatures in late winter did not delay the timing of the spring breeding season, but the number of breeding females declined. However, atypically cold temperatures in early spring delayed the timing of post-torpor activity. The evolution and adaptive nature of precise breeding periods and a flexible schedule with regard to seasonal emergence are postulated and related to the ecology of chipmunks in southeast Ohio.

Feeding Ecology of a Population of Eastern Chipmunks (Tamias striatus) in Southeast Ohio

Food resource fluctuation and composition of diet were continuously monitored for a population of eastern chipmunks (Tamias striatus) in SE Ohio from May through October 1975. Three food categories were used extensively by the population: plants, invertebrates, and fungi. Chipmunks selected subsets of the food available in each category. Plant material formed the bulk of spring and autumn diets. The relative proportion of invertebrate and fungal food in diets increased during summer. Adult males consumed significantly more plant and less invertebrate material than did other age-sex classes. Regression analysis revealed positive relationships between invertebrate and fungal availability and their percentages in the diet. Chipmunk activity was positively related to fungal consumption and inversely related to plant (reproductive structure) consumption. Explanations are offered for the trends observed. Discriminant analysis revealed a distinction between adult and juvenile feeding behavior based on invertebrate consumption, adults consuming smaller amounts of invertebrate food. In addition, adult feeding behavior was consistent while that of juveniles was interpreted as being adaptively flexible.

Bacterial contents of the anal and castor glands of beaver (Castor canadensis)

Bacterial contents of both the anal gland and castor gland of the beaver (Castor canadensis) were determined. Using our culture methods, no bacteria were isolated from the castor glands, but the anal gland contained high numbers of the aerobeEscherichia coli and the anaerobeBacteroides fragilis. The latter may be represented by several variants but facilities were not available for advanced anaerobic analysis. The relative numbers of each bacterial group and the group present were constant regardless of sex, age class, or colony of beaver. The bacterial fermentation hypothesis is rejected for castor gland section but remains possible for anal gland secretions based on variations seen inB. fragilis. The role of the products of both the castor gland and anal gland are discussed in relationship to scent communication in beaver.

A Field Bioassay of Beaver Castoreum and Some of Its Components

The response of free-living beavers (Castor canadensis) to castoreum and some of its components was determined through a series of field bioassay experiments in southeastern Ohio. Beavers responded to test scents containing castoreum and the neutral and phenol components but not the carboxylic acid and amine components. Urine from the bladder did not attract beaver, whereas urine after it passed the castor sacs and mixed with the contents of the castor sacs was an attractant. No seasonal difference characterized the response to castoreum, and the response to castoreum from adult male and female beavers was not different. The function of odor profiles of beaver and scent mounds are discussed.

Spatial-Genetic Structure in the Eastern Chipmunk, Tamias striatus

Spatial autocorrelation is used to identify the pattern of allozyme variation in populations of the eastern chipmunk ( Tamias striatus ). A nonrandom pattern of autocorrelation was detected when distances several hundred times the distance across an average home range were considered. A population sufficiently large to survey demographics and the mating system (across several dozen home ranges) was deemed too small for genetic studies. The size of the genetic neighborhood of the chipmunk was estimated from a correlogram. These results are interpreted to mean that it is possible to identify the size of the genetic neighborhood by use of spatial autocorrelation and that it is an appropriate preliminary analysis for identifying the limits of dispersal and gene flow.