Reproduction and survival rates of female grizzly bears were used to estimate the population trend of the Yellowstone grizzly bears. The study area centered around Yellowstone National Park, but encompassed roughly twice its area at about 20,000 km2. The authors found that Yellowstone grizzly bear populations appear to be increasing, although they caution the interpretation of the results because of the wide confidence interval (95%). They also suggest there may be significant bias in the parameter estimates because of lost radio collars, use of bear-years to estimate survival in equations, and inability to follow all specimens until death. They agree that further study of possible biases on the estimates need to be done, as well as more telemetry to increase samples. They also suggest that if numbers are increasing, lack of habitat will eventually result in cessation of population growth. This will most likely be evident in subadult survival. Therefore subadult survival may be helpful in future monitoring.