Climate change has caused migratory birds to shrink in size

Dec 18 (Agencies) | Publish Date: 12/18/2019 10:57:21 AM IST

 Climate change has caused migratory birds in North America to shrink in size — while their wings grew longer — over the last 40 years, a study has found.

Researchers from Chicago and Michigan studied more than 70,000 small, migratory song birds that had been collected after fatal building strikes. 

Scientists have long known that individuals from a given animal species tend to be smaller in warmer parts of their habitat — a pattern dubbed 'Bergmann's rule'. Although it had been wondered if climate change might also be triggering shrinking body sizes, evidence to support this hypothesis had been inconclusive until now. 

Field Museum ornithologist and collections manager David Willard measured 70,716 birds from 52 species as part of the study, recording their body sizes and shapes.

The collection focuses on small-bodied songbirds, with species of sparrow, warbler and thrush making up the majority of those studied. The birds themselves were retrieved after fatal collisions with Chicago buildings during both spring and autumn migrations — with such collections been undertaken each year since 1978. Analysing the vast dataset, researchers found that the body sizes of all 52 species studied have been decreasing over the last four decades — with statistically significant shrinking seen in 49 species. 

(Ian Randall for mailonline)

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