Climate change was meant to mean big trouble for Bicknell’s thrush. One of North America’s rarest songbirds, the species was already struggling with mercury poisoning and habitat loss. As the bird’s mountainous home warmed, ecologists worried that a new threat would move in: the American red squirrel, a mammal that will supplement its seed-rich diet with songbird eggs and nestlings.
The squirrels are found downslope of the thrushes and were expected to move up the mountainside as temperatures rose. Toni Lyn Morelli, an ecologist at the University of Massachusetts Amherst, discovered that the squirrels have actually begun moving downhill. It is good news for songbird conservationists, but puzzling news for ecologists more generally.
The squirrels seem to be heading the wrong way. Can everyone live a ‘good life’ without destroying the planet? In some locations, as many as half the species studied are defying the prediction that they would shift to cooler places.
The discovery is making it difficult for conservationists and land managers to protect vulnerable species. Working on the assumption that the species would move away from the heat, they have been conserving or buying up cooler areas they assumed would become climate refuges. But what if they are protecting land in the wrong places?
Researchers are now going back to basics in order to understand what is going on, and to devise conservation strategies that are a better fit for our warming world. For most of the past 30 years, ecologists have assumed that climate change-driven range shifts would be largely one way: into colder places. The first good evidence for this came in 1996 when Camille Parmesan, then at the University of California, Santa Barbara, demonstrated that the Edith’s checkerspot butterfly in western North America was quitting the increasing warmth of its southern, low-elevation habitats for the cool of higher and more northerly climes.
By 2003, Parmesan, along with Gary Yohe at Wesleyan University in Connecticut, was even quantifying the rate of the shift. Using data from hundreds of animal and plant species, they calculated that, every decade, species were moving an average of about 6 metres uphill or 6 kilometres towards the poles. That rate was later revised upwards.
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