An analysis of a population of snowshoe hares, Lepus americanus washingtonii Baird, in western Oregon

Graduation date: 1965The ecology of a population of snowshoe hares, Lepus\ud americanus washingtonii, was studied in western Oregon from 1960\ud to 1962. Objectives were to obtain information to control hares,\ud which frequently cause damage to coniferous reproduction in the\ud region, and to compare the life history of this little-studied subspecies\ud with others.\ud The study area was located on cut-over forest land at 2900-foot elevation in the western Cascades. The climate is characterized\ud by heavy precipitation in winter and summer drought. Snowfall is\ud slight.\ud Sixty-four live-traps were located in a square grid of 8 rows\ud of 8 traps each, at spacings of approximately 100 and 200 feet. Half\ud the traps were located on a recently clear-cut area and half in young-growth\ud western hemlock and Douglas-fir. Traps usually were set\ud for three successive days at monthly intervals. Trapped hares were\ud marked and released on the main study area, and hares from nearby\ud areas were removed for necropsy.\ud In all, 207 hares were caught 889 times on the trapping grid\ud during the 18-month study. One-third of hares tagged and released\ud were not recaught, but the remainder were recaught one or more\ud times. Trapping success varied from 3.6 to 44.4 percent. Principle factors influencing movements of hares, trapping success, and\ud distribution of catches were vegetative structure, weather, and\ud differing behavior of adults.\ud Estimates of numbers of hares were computed from live-trapping data by the recapture, and the calendar-graph methods. Both\ud methods indicated comparable trends in the population. Estimates of\ud hares on the area trapped ranged from 41 in March to 136 in August.\ud Estimated density of hares was 1.6 per acre at start of trapping in\ud October. Density was nearly doubled to about 3.0 hares per acre in\ud late summer.\ud Most adult females on the area studied had two or three litters\ud a year, averaging three young per litter. First litters were born in\ud May and last litters in August.\ud Most juveniles approached maximum size by four months.\ud Mean total length of adults of both sexes was greater than that of subadults.\ud Foot and total length of adult females were greater than in adult males. Mean weight of adult males in winter was 40.6 ounces\ud and of females, 43.4 ounces. Subadults and adults weighed slightly\ud less in early winter than in late fall.\ud Sex ratio of 205 adult and juvenile hares was 80 females to\ud 100 males; ratio of 84 young juveniles tagged during the summer was\ud 87 females to 100 males. Juveniles tagged (154) exceeded adults\ud tagged (51) by a ratio of 3:1.\ud Weighted mean range-size of adult hares caught three or more\ud times as computed by the inclusive-boundary-strip, and circular-bivariant-distribution methods was 5.76 and 10.15 acres for males;\ud 3.30 and 7.80 acres for females. Mean home range of juveniles was\ud comparable to the range of adult females. Distribution of catches of\ud hares repeatedly caught and tracking of toe-clipped hares showed that\ud trap-revealed ranges are related to true ranges and that ranges of most\ud adults are fairly stable. A tendency towards farther ranging and linearity of movements was shown by some hares in winter. Location and use\ud of forms are described. Signs of feeding showed that hares fed on conifers and shrubs in winter and herbaceous vegetation in summer.\ud Young juvenile hares "disappeared" from the population at a\ud high rate. Probability of their survival from birth to the first breeding season was less than 0.18. Crude survival rate of all hares was\ud 0.73.\ud Neither disease nor parasitism constituted serious decimating\ud factors, and pathology of 74 hares necropsied was normal. Predation\ud was the most important source of mortality among hares of all ages.\ud Symptoms of "trap sickness" were shown, mainly in winter, by 29\ud of 207 hares.\ud The following parasites were found in 50 necropsied hares,\ud and 207 hares examined for ticks and fleas: Protozoa, Eimeria\ud stiedae; Cestoda, Mosgovoyia pectinata americana, and Taenia\ud pisiformis; Nematoda, Trichostrongylus affinis, and Nematodirus\ud triangularis; Acarina, Haemphysalis leporis-palustris; and\ud Siphonaptera, Cediopsyllus simplex and Hoplopsyllus affinis