Graduate Thesis Or Dissertation
 

Habitat and distribution of pygmy rabbits (Sylvilagus idahoensis) in Oregon

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  • The objectives of this study were to determine the location and extent of populations of pygmy rabbits in Oregon, and to describe several biotic and physical components within communities that include pygmy rabbits. Interpretation of aerial photographs, and information obtained from soil maps and interviews with biologists and area residents, were used to direct the search for sites occupied by rabbits. This search was conducted June to October 1982 and generally was limited to areas where pygmy rabbits were collected previously. Sign of pygmy rabbits was observed at 51 of 211 sites examined. Soil and vegetation components were sampled July to October 1982 at 15 sites occupied by pygmy rabbits, and 21 sites adjacent there to. Mean soil depth at sites occupied by pygmy rabbits was 51.0+2.3 cm, and was significantly greater than at adjacent sites (31.0+3.1 cm). Soil strengths of surface and subsurface horizons at sites occupied by pygmy rabbits were 0.8+0.2 and 3.8+0.3 kg/cm², respectively, and were significantly less than at adjacent sites (1.9+0.4 and 4.6+0.2 kg/cm²). Soil depth and soil strength, more than soil texture, were physical properties that distinguished sites occupied by pygmy rabbits from adjacent sites. Soil properties associated with habitats of pygmy rabbits probably were related to excavation of burrows. Shrub height (84.4+5.8 cm) and shrub cover (28.8+1.4%) at sites inhabited by pygmy rabbits were significantly greater than shrub height (52.7+5.3 cm) an shrub cover (17.7+1.2%) at adjacent sites. The affinity of pygmy rabbits for greater shrub cover and shrub height possibly was related to avoidance of predators and availability of forage. No significant differences between sites occupied by pygmy rabbits and adjacent sites were obtained for percent basal area of perennial grasses, annual grass density, forb density, or cryptogam cover. Analysis of 472 samples of Artemessia tridentata collected at and near areas inhabited by pygmy rabbits in Oregon indicated presence of pygmy rabbits was not dependent upon distributions of specific subspecies of A. tridentata. A marked decrease in activity of pygmy rabbits at sample sites the second year of this study demonstrated populations of pygmy rabbits were susceptible to rapid declines and possibly local extirpation. Fragmentation of sagebrush communities poses a potential threat to populations of pygmy rabbits, but the severity of this threat presently is not known.
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