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Mule Deer Survival in Colorado, Idaho, and Montana
James W. Unsworth, David F. Pac, Gary C. White and Richard M. Bartmann
The Journal of Wildlife Management
Vol. 63, No. 1 (Jan., 1999), pp. 315-326
Stable URL: http://www.jstor.org/stable/3802515
Page Count: 12
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We examined survival rates of mule deer (Odocoileus hemionus) fawns (1 Jan-31 May) and adult (≥1 yr old) females (1 Jun-31 May) from Colorado, Idaho, and Montana to assess the influence of survival on population dynamics over a broad geographic area. Survival rates were estimated from 1,875 radiocollared fawns and 1,536 radiocollared adult female-years. We found significant year-to-year differences in overwinter survival rates of fawns among states (P < 0.001), while annual survival rates of adult females showed less variation across years (P < 0.256). Sampling distributions of survival rates by age class were modeled with the beta-binomial distribution (BBD) and not found different among states (ad F: P = 0.118; fawns: P = 0.856). The mean overwinter survival rate for fawns was 0.444 (SE = 0.033), with SD = 0.217 (SE = 0.019). The mean annual survival rate for adult females was 0.853 (SE = 0.011), with SD = 0.034 (SE = 0.014). All 3 states exhibited differences in body size of fawns at the start of winter across years, and body size was a predictor of overwinter survival (P < 0.001). Fawn sex ratios in December at time of capture were not different from 50:50 (P = 0.729). However, a sex differential in overwinter survival of fawns was observed (P = 0.002), but beta-binomial models of survival distributions were not different between sexes (P = 0.458). Frequencies of 3 categories of proximal causes of fawn mortality (predation, winter malnutrition, other) differed among states (χ 2 4 = 41.24, P < 0.001). A deterministic model with a mean winter survival rate of 0.444 for fawns and an annual rate of 0.853 for adult females predicted December fawn: doe ratios would have to be at least 66: 100 to maintain population levels. Similarity of mule deer population dynamics across the 3 states suggests similar processes regulate these populations; hence, results from specific study areas are generally more applicable than commonly thought.
The Journal of Wildlife Management © 1999 Wiley