1982 年 14 巻 2-3 号 p. 179-186
House Finches introduced in eastern North America from western California stock in 1940 have become setablished in the east. The new population has developed slightly shorter wings and tails and markedly shorter tarsi and toes, but significantly larger bills than those appendages of the California population from which they were descended. Shorter wings and tails, if indicative of body size, may be correlated with a more moist climate in eastern North America. Shorter legs and toes suggest adaptation by eastern birds to colder climate in accordnace with Allen's rule, or they may indicate adaptation to feeding from perches rather than on the ground. Increase in bill size may be an adaptation to greater size of food items, such as sunflower seeds at feeding stations, required particularly during severe winter weather encountered in the east but not in California. Small weed seeds are the primary winter food of California House Finches while the new eastern population depends heavily in winter on food provided at feeding stations where sunflower seeds, which are much larger than the native foods, are preferred. Adaptation in ability of indiviadual birds to handle the large sunflower seeds may have favored survival of those individuals with larger bills among the founders of the eastern population.