Climate Change Linked to Shrinking Birds

Photo: Scarlet Tanager.
Courtesy of TheMarvelousInNature from Flickr

Certain birds in North America are getting smaller, according to a paper published last year in the journal Oikos and covered in the October issue of The Scientist.

Researchers from the University of Zϋrich found that more than 100 bird species have shrunk in size over the past half of a century. This appears to be driven by climate change, since smaller body size and wing length provide an advantage in a warmer climate. What that advantage may be, is still unknown. However, it is well known that animals that live in warmer climates tend to be smaller. The changes observed could be the result of bird species adapting to a warming earth.

About half a million birds were weighed and measured in the study. On average, a species’ body mass shrunk by 1.3%. Some species, like the rose-breasted grosbeak, lost 4% over the 46-year study period. The most affected bird species were North American songbirds, but the pattern was also found in birds that spend the winter in the Caribbean and South America. The BBC’s coverage of the study includes more details and is worth checking out.

While it’s not easy to say whether these changes will have long-term effects on the bird populations studied, they have raised concerns about the consequences of a warming planet for birds.

“The fact that this selection seems to be favoring small birds and that the birds are getting smaller both suggests that the decrease in size is an adaptive response . . . But the problem is to what extent can you keep adapting in that way? If it keeps getting warmer, and you keep having to select for small size, then eventually you are going to see the consequences of that,” said Ary Hoffmann, commenting on the paper in The Scientist.