(p. D3) More than a century ago, zoologist Joseph Grinnell launched a pioneering survey of animal life in California, a decades-long quest — at first by Model T or, failing that, mule — to all corners and habitats of the state, from Death Valley to the High Sierra.
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In 2003, museum scientists decided to retrace Grinnell’s steps throughout the state to learn what changes a century had wrought. And that’s why Morgan Tingley, then an ecology graduate student at the university, found himself trekking through the Sierra for four summers.
Dr. Tingley wanted to know how birds had fared since Grinnell last took a census. Years later, the answer turned out to be a bit of a shock.
Of 32,000 birds recorded in California mountain ranges in the old and new surveys — from thumb-sized Calliope hummingbirds to the spectacular pileated woodpecker — Dr. Tingley and his colleagues discovered that most species now nest about a week earlier than they did 70 to 100 years ago.
That slight advance in timing translates into nesting temperatures about two degrees Fahrenheit cooler than the birds would encounter had they not moved up their breeding time — almost exactly counterbalancing the two-degree rise in average temperatures recorded over the last century.
The scientists’ analysis, published last fall in the Proceedings of the National Academy of Sciences, showed that the birds’ temperature-rebalancing act could limit the exposure of eggs and fragile nestlings to dangerous overheating.
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The study of 202 species showed that most of them are adapting to rising temperatures with “overlooked flexibility,” the scientists reported — unexpected hope for wildlife in an uncertain time.
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Ecologists generally believe that birds adapt to rising temperatures by moving to higher elevations or heading north. They shift their nesting time for a different reason: to sync with food availability, like an early appearance of plump caterpillars or swarms of insects.
But in 2012, researchers found that about half of the bird species in certain regions of the Sierra essentially stayed put over the past century, not significantly extending their ranges to cooler elevations even though the climate was warming.
The new study offers a plausible explanation. If the birds lay their eggs earlier, they can stay in their centuries-old range, with no need to migrate to higher altitudes.
“Ecologists have really kept range shifts like migrating upslope separate in their minds from phenological shifts, such as nesting earlier,” said Peter Dunn, an ecologist at the University of Wisconsin-Milwaukee, who was not involved in the new analysis.
“The research makes you realize that birds can manipulate all sorts of things, not only spatially by migrating upslope but also temporally — shifting their nesting time in response to rising temperatures.”
For the full story, see:
Wallace Ravven. “Survival of the Shrewdest.” The New York Times (Tuesday, July 31, 2018): D3.
(Note: ellipses added.)
(Note: the online version of the story has the date July 30, 2018, and has the title “‘California’s Birds Are Testing New Survival Tactics on a Vast Scale.”)