Out of Sync

Wildlife is at risk as global warming changes the timing of seasonal behaviors such as breeding and migration

  • Laura Tangley
  • Apr 01, 2005

ON A MUGGY, moonless night last June, a loggerhead sea turtle hauled herself out of the Atlantic Ocean onto a quiet Florida beach and slowly crawled to the base of the dunes. Over the next hour, the 300-pound reptile dug a deep, urn-shaped hole in the sand with her rear flippers, deposited 120 soft, white, golf-ball-sized eggs, filled in the hole and dragged herself back to sea, fulfilling an ancient rite that has changed little since sea turtles evolved more than 100 million years ago. Standing at the water’s edge, biologist John Weishampel watched the primeval creature disappear in the surf. “If there’s one thing you can say about sea turtles,” he noted, “it is that they are remarkably consistent.”

At least until now. Weishampel, an associate professor at the University of Central Florida, recently analyzed long-term records from this 25-mile stretch of Florida coast, the Western Hemisphere’s most important nesting beach for the threatened loggerhead. He discovered that turtles today are coming ashore to lay eggs about 10 days earlier than they did as recently as 1989. Suspecting that global warming was accelerating the cold-blooded animal’s life cycle, Weishampel next looked at water temperature data collected offshore. He found these temperatures had increased by some 1.5 degrees F during the same 15-year period.

In some ways, his results, published last November in Global Change Biology, are not surprising. As global temperatures continue to rise, scientists around the world are discovering that the timing of seasonal events in the life cycles of plants and animals is shifting rapidly and dramatically. Trees, for example, are budding earlier and losing leaves later, while animals are migrating, mating, producing young and emerging from hibernation sooner. Though Weishampel’s study is the first to note the phenomenon in a reptile, it has been well documented in a wide variety of animals, from insects and fish to frogs, birds and mammals.

Some of the most recent and convincing evidence comes from a November 2004 report from the Pew Center for Global Climate Change. The study summarizes more than three dozen scientific reports linking global warming to ecological changes in the United States alone. These shifts, the report notes, are consistent across species, ecosystems and geographic regions throughout the country.

Among the report’s findings: Plants in Washington, D.C., are flowering 4.5 days earlier than they did 30 years ago; Mexican jays in southern Arizona breed about 10 days sooner than they did in 1971; male frogs in Ithaca, New York, begin courting females 10 to 13 days earlier than a century ago; and barn swallows nationwide are nesting about 9 days sooner than they did in 1959. In each case, the species’ behavioral change coincides with a temperature increase during the same period. According to report coauthor and University of Texas biologist Camille Parmesan, the document demonstrates that “climate change is happening right here, right now, and changing life in your own backyard.”

What worries biologists like Parmesan is that any given species is unlikely to respond to changing climate in the same way as others that share its habitat. When this happens, vital links among interdependent species—such as a plant and its pollinator—can be broken, a loss of synchrony that not only threatens each partner in the relationship, but may also disrupt entire plant and animal communities. “In nature, timing is everything,” says Weishampel. “It’s like a symphony that’s ruined if one instrument comes in at the wrong time.”

Such fears are substantiated in a recent report, Global Climate Change and Wildlife in North America, published by The Wildlife Society. Gathering together results of hundreds of studies that forecast consequences of global warming, the document warns of potential upheavals of natural communities nationwide and possible disappearance of some wildlife habitats, including New England’s conifer forests. Says NWF Senior Science Advisor Doug Inkley, chairman of the committee that wrote the report, “Global warming presents a profound threat to wildlife in this country, a threat that may equal or even surpass the effects of habitat destruction.”


So far, only a handful of studies have been conducted long or comprehensively enough to document the impact of climate change on interdependent species. In one, biologist Marcel Visser has been monitoring great tits—European birds similar to chickadees—in a national park near his office at the Netherlands Institute of Ecology for the past 20 years. Springtime temperatures in this region have climbed about 3.6 degrees F during the past two decades, but Visser says tits are laying their eggs at about the same time as when he began his work. The problem is that winter moths—whose caterpillars nourish the birds’ chicks—apparently are responding to temperature changes. Today the insects reach their peak abundance about two weeks earlier than they did 15 years ago, putting the birds out of sync with their most important food source.

Meanwhile, the caterpillars themselves have gotten out of sync with their primary food, fresh oak leaves, hatching before leaf buds even open. So far, Visser has observed no decline in the park’s great tit numbers, but he believes such decreases are “only a matter of time.” Winter moth populations are already falling.

In the U.S. Rocky Mountains, biologist David Inouye sees the potential for similar problems. Since 1971, Inouye, a professor at the University of Maryland, has been monitoring a variety of plant and animal species at the Rocky Mountain Biological Laboratory in Colorado. One of his discoveries is that American robins are arriving to breed about two weeks earlier than they did in the late 1970s, apparently in response to warmer temperatures in their low-altitude winter habitat. But conditions at the 9,662-foot field station have not changed as significantly. When many robins arrive now, it’s still winter, and the birds must wait for snow to melt before beginning to feed and breed—a delay that may decrease both the number and survival of their chicks.

Likewise, yellow-bellied marmots are responding to higher spring air temperatures by leaving hibernation dens more than a month sooner than they did a few decades ago, so soon that snow covering plants they eat has not completely melted. Since 1993, says Inouye, “a regional climate shift superimposed over global warming” has decreased snowfall, offsetting the problem somewhat. “But if the mismatch between cues at lower and higher elevations keeps growing,” he says, “these animals could be in trouble.”

Neotropical migrants, songbirds that travel long distances between their wintering and breeding habitats, face even greater challenges. These birds “are coming from the tropics, a place that’s experienced relatively minor changes, to one that’s been altered significantly by global warming,” explains ornithologist Peter Marra of the Smithsonian Environmental Research Center. “There’s no way for them to know what the climate is like thousands of miles to the north.”

On the Edge 
Polar Bears Suffer Meltdown

For wildlife in a warming world, getting out of sync with one’s environment can be just as risky as losing a critical plant or animal species—as a long-term study of polar bears on the western shore of Canada’s Hudson Bay illustrates all too clearly.

For the past three decades, Canadian Wildlife Service scientist Ian Sterling has been studying these bears, which from spring to summer use the bay’s sea ice as a base for hunting seals, their primary food.

But the ice is melting two weeks earlier than it did 20 years ago, and Sterling has found that bears today weigh less and give birth to fewer cubs. For every week the ice breaks up sooner, the animals are 22 pounds lighter.

Meanwhile, the bay’s ice continues to melt earlier and earlier each year. “If all the ice goes in Hudson Bay, as the forecasts predict, there won’t be any polar bears there,” says Sterling. “And there’s no place else they can go.”

Because temperatures in the tropics tend to be relatively stable year-round, scientists have assumed that migratory songbirds rely on internal physiological cues or changes in day length to determine when to start migrating. To investigate whether the birds can adjust their behavior to be more in sync with changed conditions in the north, Marra and his colleagues analyzed 40 years of data on temperature and springtime arrival dates of 15 songbird species—including warblers, wood thrushes and tree swallows—at research stations in Pennsylvania and Ontario, Canada.

The scientists found that for every 1 degree C (1.8 degree F) increase in springtime temperature at the breeding sites, migrants were arriving one day earlier, probably because they were able to pick up cues en route—such as earlier greening or more insects to eat—and begin traveling faster. But migrants still were not keeping pace with plants in the breeding habitat (and presumably insect prey the plants support), which were budding three days sooner with each degree of warming. In addition, says Marra, “there’s probably a limit to the birds’ flexibility. Migratory birds evolved to cope with gradual climatic changes, but the changes today are happening much faster.”

One creature that’s not coping very well is Edith’s checkerspot butterfly, a delicate orange, black and white- checked insect less than two inches long that inhabits the west coasts of northern Mexico, the United States and southern Canada. According to Parmesan, who has studied the species for two decades, its distribution appears to be contracting. In the southern portion of the butterfly’s range, 80 percent of its populations—including an endangered subspecies, the Quino checkerspot—have become extinct. Responding to warmer temperatures, the plants on which the butterflies lay their eggs are drying up before the caterpillars hatch, leaving the tiny larvae to starve.

That’s what Weishampel fears could happen to loggerheads off the coast of Florida. While nesting females do not eat, hatchlings that emerge from their eggs two months later feed voraciously on clams, crabs, shrimp and other tiny marine invertebrates. “We have no idea how warmer ocean temperatures are affecting these critical food species,” says Weishampel.

Already, there are signs that Florida’s loggerheads may be in trouble. Since 1999, the number of turtle nests counted on a 13-mile stretch of beach within Archie Carr National Wildlife Refuge have been declining each year—after a record high of 17,629 seven years ago. Last year’s total, 7,599 nests, was the lowest ever recorded since researchers began monitoring the beach decades ago.

Biologist Llewellyn Ehrhart, professor emeritus at Central Florida University and distinguished senior research fellow at Hubbs-Sea World Research Institute, has been working with loggerheads on this beach for more than 30 years. Noting that nest numbers naturally fluctuate—with record high years followed by two or three low ones—Ehrhart says, “It’s not time to hit the panic button yet.” But if the numbers are still down in 2005, he adds, “Something’s definitely wrong.”

That something could turn out to be any of a number of problems scientists have observed in recent years. One is a mysterious disease that a few years ago caused scores of comatose loggerheads to wash ashore on Florida beaches. Another is beach erosion, brought on by a combination of coastal development and sea level rise. And last year, in addition to a record low number of loggerhead nests, a series of powerful hurricanes wiped out 44 percent of the nests before the eggs hatched.

Of course, stronger hurricanes, higher sea levels, and an upswing in wildlife disease are also among the projected consequences of global warming. It could turn out that, even for a creature that survived the upheavals that wiped out the dinosaurs, the world is changing just too fast today.

Laura Tangley is a senior editor for this magazine.

Wild Life On The Hot Seat

Changes in the timing of seasonal behaviors are only some of the ways global warming has affected wildlife. Species also are on the move, with their ranges shifting for the most part northward or to higher elevations. Distributions of some species, particularly those that have small ranges or live at the edge of suitable habitat, are contracting, while a handful of others are expanding. As with all major changes, there are winners as well as losers, yet the losers include some of Earth's most vulnerable and endangered wildlife. Beyond shifts at the species level, entire communities are being transformed as plants and animals in the same habitat respond differently to climate change. According to Stanford University biologist Terry Root, coauthor of The Wildlife Society report Global Climate Change and Wildlife in North America, "In the future, well-balanced wildlife communities as we know them will likely be torn apart."

On Alaska's Cooper Island, populations of black guillemots are declining as sea ice recedes, taking with it the birds' primary prey: Arctic cod, which live under the ice. For more information visit: www.cooperisland.org

Extremely high water temperatures accompanied by drought-induced low water flows led to the 1998 deaths of tens of thousands of sockeye salmon in British Columbia-a preview of what's to come, say some scientists.

Between 1987 and 1994, the number of sooty shearwaters off the U.S. west coast decreased by 90 percent. Some scientists attribute the decline to changes in ocean temperatures and currents caused by global warming.

In Monterey Bay, California, the ranges of intertidal invertebrates such as limpets and snails have been shifting northward for the past six decades as sea and air temperatures rise.

The distribution of Edith's checkerspot butterfly, which extends from the west coast of southern Canada through northern Mexico, is contracting. In the southern portion of the butterfly's range, 80 percent of all populations have become extinct.

In southern Arizona, the breeding season of the Mexican jay advanced by 10 days between 1971 and 1998. The change correlates with spring monthly temperatures, which rose 4.5 degrees F during the same period.

In Colorado, robins are migrating from low to high elevations where they breed two weeks earlier than they did in the late 1970s. Many birds now arrive before snow melts.

Scientists say warming in the U.S. Great Basin has contributed to the extinction of 7 of 25 populations of American pika. Sensitive to temperature changes, these high-elevation mammals have nowhere to move.

On Canada's Hudson Bay, early melting sea ice has decreased the amount of time polar bears have to hunt seals, their primary prey. As a result, bears today weigh less and give birth to fewer cubs than they did 20 years ago.

These migratory birds are arriving at their breeding grounds in northern Michigan 21 days earlier than they did in 1960.

In western Long Island Sound, large numbers of lobsters died mysteriously during September 1999. Some researchers suggest that high water temperatures wiped out the crustaceans, which were living at the southern limit of the species' range.

For nearly two decades, prothonotary warblers have been returning to breeding grounds in Virginia from wintering grounds in South America and the Caribbean a day earlier each year as springtime temperatures rise.

The distribution of the American alligator, which ranges from the Carolinas south to Florida and west to Texas, appears to be shifting northward in some regions. Rising sea level may also force the freshwater reptiles inland, where they would encounter more development.

Off the Atlantic coast of Florida, threatened loggerhead sea turtles are coming ashore to nest 10 days earlier than they did in 1989. During the same period, offshore ocean temperatures have increased 1.5 degrees F.

Off the shores of many Caribbean islands, higher water temperatures are causing corals to expel their symbiotic algae-or bleach-which can lead to coral death and damage to entire reef ecosystems.

In the first species extinction attributed to global warming, the amphibians have disappeared from their only known habitat, Costa Rica's Monteverde Cloud Forest.

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