The Best American Science and Nature Writing 2014 Read Online Free Page B

populations are plummeting, and scientists are wary of the species’ chances for long-term survival. “If [this decline] continues at the rate it has been going, we could see drastic reductions in their populations or, worst-case scenario, extinctions,” says Vallender. “We need to do this research now.”
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    What’s happening to the two warblers isn’t unique. Polar bears and grizzly bears are mating, as are different species of everything from butterflies to sharks.
    In some instances, it’s clear that climate change is playing a role. More than 1,700 animal species across the globe have shifted their ranges northward and upward in elevation, searching for colder temperatures and following as the plants and other animals they rely on shift as well. Ice sheets and other physical barriers that once kept species apart are disappearing. All of these changes are expected to accelerate as we spew ever more greenhouse gases into the atmosphere, driving up the earth’s temperature.
    Climate-driven intermixing is raising challenging conservation issues. Should hybrid offspring be protected if one parent species is threatened or endangered? Ecologically, does it matter if the world loses purebred species to hybridization? Is it best to get involved or to let nature take its human-altered course, creating new species and eliminating others? These are the questions experts are just beginning to ponder, even as the planet continues to warm.
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    In 2006 an American big-game hunter from Idaho shot and killed the first documented wild polar–grizzly bear hybrid, a mostly white male covered in patches of brown fur, with long grizzly-like claws, a humped back, and eyes ringed by black skin. Four years later a second-generation “pizzly” or “grolar” was shot. After hearing reports of the bears, Brendan Kelly, then an Alaska-based biologist with the National Oceanic and Atmospheric Administration, started to wonder which other species might be interbreeding as a result of a changing Arctic landscape.
    Snow and sea ice hit record lows in 2012, and the Arctic has warmed more than 3.6 degrees Fahrenheit since the mid-1960s, more than twice the global average.
    To gauge what kinds of effects these shifts were having on Arctic animals, Kelly teamed up with the biologist David Tallmon at the University of Alaska and the conservation geneticist Andrew Whiteley at the University of Massachusetts Amherst. The trio coauthored a seminal report for the journal
Nature
in 2010 that chronicled the hybridization that wildlife managers and First Nations communities had been seeing in the Arctic, including the mixing of beluga whales and narwhals, bowhead and right whales, Dall’s and harbor porpoises, hooded and harp seals, spotted and harbor seals, and North Atlantic minke and North Pacific minke whales, in addition to polar and grizzly bears. They also outlined the devastating effects the new genetic exchanges could have on biodiversity, such as parent species being driven to extinction or creating hybrids unable to survive in the environments they are born into.
    The scientific community at large quickly recognized that the genetic mixing wasn’t limited to animals in the rapidly changing Arctic. Today they’re finding it all over the place, in owls, petrels, squirrels, big cats, and wild canines.
    Between 2007 and 2009, researchers from several Australian universities caught fifty-seven hybrid blacktip sharks while doing routine marine surveys off the northeast coast of Australia. Genetic tests confirmed that they were crossbreeds of Australian and common blacktips. The result of several generations of interbreeding, they were found south of the tropical areas where Australian blacktips typically live.
    Elsewhere, scientists are discovering that hybridizing species are exchanging behavioral and physiological traits, not just physical ones. Mark Scriber is an entomologist and