Fun with Science Club®


			Is having a big body bad in warm weather? Maybe for birds. Carrie Straight 05.18.01 Along with changing the abundance and distributions of many animal species, global warming has changed the lifestyles of many animals. In science, there are general rules that most animal body sizes and shapes follow. Bergmann’s rule says that in warmer environments warm-blooded animals are smaller than those from colder environments. These differences would allow larger animals to stay warmer in cold climates and smaller animals to get rid of excess body heat in warmer climates. Following this rule, one scientist from Israel predicted that because of global warming the body sizes of birds (their weights and the lengths of their lower leg, the tarsus) might have decreased over the last 50 years. To test this prediction, this researcher set off for the museum. He chose 5 small bird species to study (graceful warbler Prinia gracilis, house sparrow Passer domesticus, yellow-vented bulbul Pycnonotus xanthopygos, Sardinian warbler Sylvia melanocephala, and crested lark Galerida cristata). Over the years specimens of these birds were brought to the museum for the collection. People at the museum weighed them and measured the tarsus, before they stuffed them. This researcher took the data from the museum collection to analyze the differences in weights and leg lengths from 1950 to 1999. From 1950 to 1999, the weights of all of the birds but the crested lark decreased. The tarsus length decreased over the years for only the graceful warbler and the house sparrow. . These changes in body sizes follow Bergman's Rule and they are consistent with the idea that global warming is occuring.


			Yom-Tov, Yoram. 2001. Global warming and body mass decline in Israeli passerine birds. Proceedings of the Royal Society of London. Biological Sciences Series 268: 947-952.