Tuesday, March 16, 2010

Shrinkage...Bergman's Rule.

According to Bergman's Rule animals tend to become smaller in warmer climates. Historically this has been demonstrated for the same species over latitude or altitude' but a question asked recently was 'given global warming could the same trend be recorded in response to climate change?'
To find out, Dr Josh Van Buskirk of the University of Zurich, Switzerland and colleagues Mr Robert (Bob) Mulvihill and Mr Robert Leberman of the Carnegie Museum of Natural History in Rector, Pennsylvania, US decided to evaluate the sizes of hundreds of thousands of birds that pass through the Carnegie Museum's Powdermill ringing station, also in Pennsylvania.
Examining records from 486,000 birds caught between 1961-2007 they found that of 83 species of spring migrant 60 had become smaller by wing length and weight; and of autumn migrants 66 out of 75 species had reduced in size. Although the time frame appears small we must remember that the birds have gone through at least 20 generations.
It appears then that north American birds are responding to Bergman's Rule however, further analysis is required as changes could be the response to other parameters affected by warmth such as food availability or metabolic rate. Furthermore, it has to be ascertained whether these changes are beneficial or otherwise. For a fuller article see: http://news.bbc.co.uk/earth/hi/earth_news/newsid_8560000/8560694.stm


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