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Conservation Science for a Healthy Planet

A Population of Billions May Have Contributed to Passenger Pigeon Extinction

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by Steph Yin November 16, 2017   read full NYTimes article here

North America was once a utopia for passenger pigeons. When European colonizers first arrived, as many as 5 billion of the gray-backed, copper-breasted and iridescent beauties roamed the continent, possibly the most abundant bird to have ever graced the planet. When they migrated, they swept across the entire sky, obscuring daylight for hours or even days at a time, the seeming embodiment of infinity. Then, in just a few decades, the inconceivable happened: Commercialized and excessively hunted, the birds vanished.

A paper published in Science on Thursday sheds new light on why the creatures went extinct so swiftly and thoroughly. Analyzing the DNA of preserved birds, the researchers found evidence that natural selection was extremely efficient in passenger pigeons.

This might have made the pigeons particularly well-suited for living in dense flocks, but unable to cope with living in sparse groups once their numbers started to plummet, the authors suggest.

Biologists generally assume that a large population corresponds to high genetic diversity, which acts as a buffer to extinction, said Susanne Fritz, an evolution expert at the Senckenberg Biodiversity and Climate Research Center in Frankfurt, Germany, who was not involved in the research.

But passenger pigeons were so plentiful and so mobile that beneficial genetic mutations spread and detrimental ones disappeared very quickly throughout their population. This caused a loss in overall genetic diversity, which meant less raw material for adapting to human-induced change.

It’s “totally the opposite of what you would expect,” Dr. Fritz said….


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