2007-08-009-C8 - Troy Hegel - Yukon Woodland Caribou Demographic Responses to Climatic and Biophysical Features
Summary
We examined how climate during different seasons influenced recruitment rates of Yukon Woodland Caribou from a number of different herds. We anticipated that climatic conditions during calving (spring) would have the greatest effect on recruitment because of how factors such as snow depth influence predation on newborn calves. Interestingly, we found that climatic conditions in the year prior to birth had the strongest effect on recruitment rates. Climatic conditions prior to the rut can influence female body condition which can reduce her chance of either successfully giving birth and/or reduce the survival of her calf. This does not mean that climatic conditions during spring are not important; they do have a statistically significant effect on recruitment. Rather, statistically, the influence of climate prior to the rut explained more of the variation in observed recruitment patterns better than springtime conditions. These results suggest that female body condition is influenced sufficiently by pre-rut climate and it is influencing recruitment rates. That climate at this time plays such a strong role in recruitment is somewhat surprising because of the high rate of calf losses shortly after birth, which means female caribou in the Yukon should be in good body condition by the rut because most do not have to provide resources for calves. Our best model of how climate influences recruitment patterns included climate from the winter prior to the rut and climate in the fall season during the rut. Poor winter conditions prior to the rut may mean the females are exiting winter in poor condition and are unable to restore their body reserves sufficiently to successfully reproduce. Good fall conditions mean that the time available for females to restore their body reserves is longer, thus enabling them to successfully reproduce. We found no effect of climatic conditions 2 years prior to the rut, which would have suggested that there is a cumulative effect of climate on reproduction which could indicate limiting forage conditions. We also investigated the effect of predator removal on the influence of climate on recruitment. From a management perspective these results provide information, which may assist in forecasting potential effects of future climatic conditions on caribou recruitment. They also suggest the importance of summer foraging conditions, and hence summer ranges, for caribou recruitment. While winter range is often viewed as a critical factor for caribou population dynamics, summer range may also be very important. These results may also be useful for managers working to predict potential effects of changing climate on caribou populations as it specifies how different seasons affect recruitment.
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