A Bird's Eye View

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They can fly but many bird species can’t hide from global climate change. Here is what’s happening and what needs to be done.

by Sharon Guynup

It’s June, and Canada’s flat, mossy grasslands are dotted with newly hatched nests of downy white snowy owls. Here at the northern fringe of the arctic tundra, the young birds’ watchful parents perch zen-like atop the nests, silently scanning for movement amidst the sedge—dinner for their hungry chicks. They also sit sentry, guarding against the stealthy approach of an arctic fox, gray wolf or other predator.

But there is a greater peril facing these birds. In certain places, the shrubs that grow farther south—dwarf birch, willow and alder—have begun to green the once-treeless tundra as earlier spring thaws and later fall freezes lengthen the growing season. These shrubs block the owls’ long, clear views across the open expanse, interfering with their ability to hunt.

Climate models predict that thawing permafrost and less extreme temperatures will bring “immigrant species” from the vast boreal forests to the south. New predators, from red foxes to ravens will be among them, animals that will stalk the ground-nesting owls with ever-more vegetation to conceal their movements.

Farther south, the saltmarsh sparrow faces a very different threat. The small, nondescript, soft-voiced songbird lives, breeds and raises its young amidst the brackish weave of salt marshes that cradle the eastern seaboard. There are ever-less of them, as their swampy homeland is relentlessly razed, filled in and developed for new and larger beach communities, strip malls, roads and more. Some 55 percent to 60 percent of Americans now live along the coasts, according to a recent United Nations report.

Saltmarsh sparrows nest on or near the ground in remaining patchwork scraps of marshland. But with slowly rising sea levels, lunar high tides now frequently swamp the birds’ nests. Ornithologists predict that this already imperiled little bird could disappear before the salt marshes do.

This is just the beginning of a trend that scientists expect to accelerate in speed and scale as climate change inexorably destabilizes global temperatures: the piecemeal reorganization of landscapes and wild habitats, with each species responding in their own way and in their own time to a warming world, shredding communities that have evolved to their current synchrony over millennia.

Despite their winged mobility and ability to disperse, birds are not exempt from the impacts of climate change, notes Defenders’ chief scientist Chris Haney. Saving species, he says, will require both research and novel conservation strategies now—and substantial reductions of greenhouse gas emissions.

The most recent U.N. Intergovernmental Panel on Climate Change models forecast average global surface temperatures to rise anywhere from 2.7 degrees F to 8.1 degrees F above 1990 levels by 2100—with the mercury soaring significantly higher at the poles.

Though that may not sound like much, a 4.5-degree-F rise would herald the greatest shift in global climate since the end of the last ice age 10,000 years ago. But present changes are occurring at biological warp speed, at a rate that many scientists consider unprecedented and that may be far too rapid for some species to adapt.

Research at Stanford University showed that in 2006 birds were already on the move. Though arctic birds have been the sentinels of extreme, rapid climate change, birds throughout the Americas—and across the globe—are shifting their home ranges toward the poles or into higher altitudes. Almost 60 percent of the 305 species that winter in North America have moved their ranges northward. Though the average is just 35 miles, some birds, such as the purple finch and pine siskin, have moved 300 or 400 miles to new nesting grounds deep within the Canadian boreal forest. The orange-crowned warbler is gaining territory as boreal forests expand into the northern tundra. Since 1970, 17 new species are summering in Vermont while others have declined or disappeared.

These changes were sparked by a seemingly inconsequential 1.3-degree-F average temperature rise above pre-industrial levels. “If they’re that sensitive, what happens when it’s 5.4 degrees F?” asks Stanford ecologist and Defenders’ board member Terry Root. Her voice is grave. “Global warming presents the greatest threat to birds and other wildlife in human history,” she says, calling it an “uncontrolled experiment.”

For birds that alter their natural ranges, life in a new neighborhood may not be a panacea. Localized conditions, from topography and rainfall to disease and human development could combine to make survival tenuous—or the new arrivals could endanger old-time ecosystem residents. One example is the resplendent quetzal, an iridescent bird with long, trailing tail feathers that was sacred to the ancient Mayans. Their nests, high in Costa Rica’s misty cloud forests, have a new invader: The lowland keel-billed toucan has moved up into the warming peaks and now preys on quetzal chicks.

There will, however, be limits for those that flee, a line where they run out of food or forestland, shoreline, mountain or grassland. A single harsh winter could devastate birds that have flown too far north, notes Caroline Kennedy, Defenders’ senior director for field conservation. Many species are also changing their biological calendars. Birds of all types, from songbirds and raptors to ducks and shorebirds, are breeding and laying eggs earlier.

 
Shift in Bird ranges by Habitat Over the Last 40 years
 

Some migrants are abandoning their wintering grounds ever-earlier in the spring. The black-throated blue warbler and rose-breasted grosbeak are two of 15 species that now reach Michigan’s Upper Peninsula three weeks before they did a half-century ago.

The conditions they find upon arrival may not be optimal. Across all landscapes, there is a growing mismatch in timing between nature’s seasonal events, with some interdependent species slipping perilously out of sync. One of these is the iconic American robin that heralds spring’s arrival in many parts of the northern United States. Populations that winter in the plains now arrive at their Rocky Mountains breeding grounds two weeks earlier than just 30 years ago. The lowlands are warmer, but they find an icy world up in the peaks. The birds encounter a food crisis, with snow still blanketing the ground for another 18 days, worms still deep in frozen soil, and last summer’s fruits and berries long gone.

But robins that breed farther east at lower altitudes have an advantage, beating out species that migrate Herculean distances for first dibs on food and prime nesting spots. Birds that breed later may also avoid certain predators. Ornithologists recently discovered that some bird populations are benefitting from the extended growing season by laying two clutches of eggs instead of just one.

Research shows that short-distance migrants are generally keeping pace with climate change. On average, they’ve advanced their travel by about two weeks, following the flush of leaves as spring greens its way northward. Following climatic cues gives them better odds of adapting over the long term than many long-distance travelers.

Birds like the great crested flycatcher and Canada warbler that over-winter in the steamy heat of the American tropics still migrate north within a few days of their old schedules. Since the weather in Panama has little to do with conditions in Maine or Michigan or Alberta, these and many other neotropical migrants use lengthening daylight to signal departure time. This means they have no concrete clue about when spring may burst out in northern climes, and may arrive too late to find adequate nourishment. Some food sources are abundant for just days or weeks. They, too, are vulnerable to changes in timing. Unless newly emerging insects and caterpillars find young, tender leaves to eat, few survive—and nestlings, in turn, go hungry.

If these climatic changes were happening in a pristine world, adaptation would be less complicated for some species, says Kennedy. But sprawling human communities, highways, farmlands and industry have already fragmented or eliminated huge swathes of habitat—and could become a fatal roadblock to shifting ecosystems. Warming temperatures will also compound existing ecological problems, creating new niches for invasive species or wider spread of diseases like avian malaria or West Nile virus. Insects that are normally knocked back by winter’s deep freeze may proliferate—like the current pine beetle invasion that’s killing off Colorado’s aspen trees—resulting in the need for more pesticide use, another negative for birds.

“There are going to be winners and losers,” says Haney. He ticks off those that are of greatest concern, specifically birds that live “at the margins” or within a limited range: arctic birds that can’t move farther north, like snowy owls; shorebirds like saltmarsh sparrows and waterfowl that face sea level rise; high mountain dwellers, like the Bicknell’s thrush, trapped on “sky islands;” those without a place to relocate or those with very specific needs, like the red-cockaded woodpecker that nests only in old, rotted-out pine trees.

But birds have several unique adaptations, Haney notes. For example, some long-haul migrants like the bay-breasted and magnolia warblers are flexible breeders, responding to yearly environmental changes. “They stop wherever they find native forests and caterpillars,” says Haney. “Breeding sites have been discovered hundreds of miles apart.”

Jeff Price, author of The Birdwatcher’s Guide to Climate Change, adds that “the winners will be the generalists, residents with widespread, broad habitat requirements like blue jays. Though they depend on oaks, there are many species of oak.”

We know that all living things are affected by temperature, but we don’t know exactly how climatic changes will play out. Only recently have modelers started accounting for factors like methane releases from melting permafrost, an example of how little we understand about the relationships between atmosphere, climate and ecosystems. This is why we must act, and quickly, says Robert Dewey, Defenders’ vice president of government relations, who has been working on legislation to address climate change. “The time is critical for a robust national response. It needs to be front-loaded so we don’t end up in triage, trying to save species when it might be too late.”

That means phasing out fossil fuels and engineering new, sustainable energy sources. At the same time, wildlife research and novel mitigation strategies are essential, like ensuring a vital set of corridors will connect habitat and allow wildlife to move with changing ecological conditions, perhaps incorporating farms and other private lands that normally are not part of the conservation equation.

Root predicts a very turbulent time ahead. “All species are in for quite a ride,” she says. But she believes that many species can be saved if we do our homework ahead of time and address existing threats to individual species and wild lands.

Defenders took that kind of preemptive step by recently convening 50 biologists and wildlife managers from across the Southeast to identify local wildlife most threatened by climate change, species like seaside sparrows and red-cockaded woodpeckers. Models show that sea level along that coastline is expected to rise by at least two feet and more intense storms will generate powerful storm surges. This group will continue to brainstorm over conservation strategies for these at-risk species.

“We can save species, but the only way we can do it is together,” says Root.

Sharon Guynup’s work has appeared in Smithsonian, Scientific American, The Boston Globe and Popular Science, among other publications. 

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