Date of Award:

1983

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Advisor/Chair:

Frederick G. Lindzey

Abstract

Mule deer (Odocoileus hemionus) reproduction and survival on the LaSal Mountains, Utah were studied from 1978-81. Reproductive rates were high, suggesting that summer and fall forage quality was adequate and was not responsible for low recruitment observed in recent years. The combined fetal rate, determined from laparotomies and carcasses, was 1.72 for all females older than 1 year (N = 114). Fetal rates were 1.15 for yearlings (N = 20), 1.80 for prime females (2-7 years, N = 78), and 1.75 for old females (8+ years, N = 16). No evidence of breeding was found among fawns (N = 18). Estimated intrauterine mortality was 3.9%. A compensatory response to inadequate winter nutrition was not identified as a factor in maintaining high reproductive potentials, although its role might have been obscured by the high predation rate on young fawns. During 1979 and 1980, an average of 67% of the total annual loss of radio-monitored fawns occurred within 54 days postpartum. Survival of transmittered fawns (N = 54) from capture to December averaged 42.7%. Direct causes of mortality during the summer included predation (73%}, primarily by coyotes (Canis latrans} and black bears (Ursus americanus}; starvation, accidents, and illegal kills (9%}; and unknown factors (18%}. Overwinter survival of fawns and does was inversely related to winter intensity. Fawn survival from January to June was 58.3% of the December population in 1980 and 88.9% in 1981. During this period, predation or probable predation, primarily by coyotes, accounted for 82% of the observed deaths and accidents for 18%. Substantial losses to malnutrition and domestic dogs occurred in Castle Valley during the severe winter of 1978-79. Total annual survival of transmittered fawns was similar both years, 28.9% for the 1979 cohort and 31.8% for the 1980 cohort. Application of a change-in-ratio estimator yielded estimates of fawn survival that were similar to survival rates from samples of radio-monitored fawns, except during summer 1979 when prenatal and immediate postpartum mortality may have been high following the severe 1978-79 winter. Annual survival rates of radio-monitored does were 68.9% in 1979 (N = 38) and 86.6% (N = 22) in 1980. Causes of death included malnutrition and predation by coyotes and domestic dogs. No mortality occurred among radio-monitored females (N = 32} between January and June 1981. Recruitment rates, estimated from spring fawn proportions were 15% in 1979, 18% in 1980, and 32% in 1981, suggesting herd declines in the first 2 years and herd growth in 1981.

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