Using Climate Data to Predict Grizzly Bear Litter Size

A 5-year double-blind test was conducted to test the predictive capability ofa previously published (Picton 1978) regression (Y =2.01 + 0.042*), which described the relationship between the litter size of grizzly bears (Ursus arctos horribilis) and an index of climate plus carrion availability (climatecarrion index). This regression showed an efficiency in excess of 99% in predicting the observed grizzly bear litter size. The predictions made using the climate-carrion index had a mean absolute error of less than 25% of forecasts using other methods. The updated climate-carrion index regression, which includes all of the 16 years for which data are available, is Y = 2.009 + 0.042.x (r = 0.78; P < 0.01; N = 16). We concluded that the climate-carrion index can be a helpful tool in predicting grizzly bear litter size. The relation of this information to the effects of the closure of Yellowstone Park garbage dumps is discussed. Int. Conf Bear Res. and Manage. 6:41-44 The prospect of a carbon dioxide induced climate change (Hansen et al. 1981) has increased the need to sharpen the tools of predictive ecology. Effective tools would make it possible to develop and take corrective management actions before the Yellow? stone grizzly bear population is severely affected by the new climate regime. Evidence for such a climate change has been increasing, and it will likely consti? tute the major environmental impact of the next 50 years (Dickinson and Cicerone 1986). The impact of such climate changes increases as one moves toward the poles. Therefore the climate impact at the latitude of Yellowstone National Park would be more severe than the global average (Kellogg and Schware 1981). This study represents a test of the predictive ability ofa regression (Picton 1978) relating the mean litter size of grizzly bears observed during the summer in Yellowstone National Park to a modified Lamb cli? mate index (1963) which includes precipitation and temperature covering the previous October to May period. This project was supported by the Interagency Grizzly Bear Study Team and the Mont. Agric. Exp. Sta. (Journal Series 1374).