Global warming, Bergmann's rule and body size in the masked shrew Sorex cinereus Kerr in Alaska

1. It was recently shown that body size of Palearctic shrews decreases with increasing latitude, thus contradicting Bergmann's rule, and this trend was explained by food shortage during the cold northern winter. In Alaska, global warming has resulted in milder winters that may improve food supply. In this study we tested the hypothesis that body size of Alaskan shrews increased during the second half of the twentieth century, in response to global warming. 2. Data on body weight and length of body, tail, hind foot and ear of museum specimens of the masked shrew Sorex cinereus Kerr from Alaska were used in order to examine the effects of latitude, longitude, mean ambient temperature in January and July, and year of collection, on these parameters. 3. We found that variation in body size of the masked shrew in Alaska appears to contradict to the prediction of Bergmann's rule, decreasing in high latitudes and in areas cold January temperature. 4. Body size of shrews in Alaska increased significantly during the second half of the twentieth century, apparently due to the higher food availability in winter as a result of improved weather conditions for its prey.