Survival of Mule Deer in Northwest Colorado

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Abstract
Survival of mule deer (Odocuileus hemionus)in Piceance Basin, Colorado, was measured with radio telemetry for 3 years on 1 study area and 4 years on another. Survival rates for deer > 6 months old were estimated for yearly intervals beginning 1 December. Male and female fawns had similar (P = 0.254) survival, as did adult and yearling females (P = 0.567). There were significant differences (P < 0.001) in survival rates among years for fawns, and for adult females, and between age classes (P < 0.001). The mean survival rate for each respective age class was 0.224 .+-. 0.056 (SE) and 0.832 .+-. 0.030 (SE). Mean fawn survival was similar on the 2 study areas even though major mortality causes differed (P < 0.001). From 46 to 76% of fawns on 1 area died from predation each year, whereas 49-83% of those on the other area starved. A Cox model analysis of 5 fawn body size variables revealed weight as the best predictor of overwinter survival. However, this was not consistent among years on 1 area, which suggested that not all mortality selected for small-bodied fawns. Average weight on 1 December was largest for fawns that lived, intermediate for fawns taken by predators, and smallest for fawns that starved. Variability in 5 body size parameters was consistently greatest for fawns taken by predators, suggesting little selection, whereas variability was smallest for fawns that lived, indicating selection for survival.

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