Warming and Wildlife » Migratory Species At Risk

At Risk: Migratory Species

Migration

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Over land, air and sea, the change of seasons triggers an annual migration of species big and small, from butterflies to birds to blue whales.

Migratory species require hospitable summering and wintering grounds and sustenance along their migratory corridors. Many have evolved with very specific migration and weather patterns and rely on the life cycles of plants and other animals. These species often bulk up in the summer to store energy for grueling migrations and long winters.

Now, global warming is throwing these environmental factors out of synch. For many species, climate change is already diminishing habitat, changing migration routes, disrupting food sources, affecting nesting and breeding habits, and increasing exposure to disease.

Some species are already changing their migratory behavior, delaying their journeys in the fall and arriving earlier in the spring. Some have abandoned migration altogether. Others are migrating to nontraditional areas.

Here are several examples of migratory species facing an uncertain future in a warming world.

Caribou: Arctic Wanderers at Risk

Migration

Alaska's Arctic National Wildlife Refuge has been called America's Serengeti. If so, the caribou is America's wildebeest.

Caribou migrate farther than any terrestrial mammal on earth, traveling as much as 3,100 miles in a year. In the fall, they move south to Canada's boreal forest where they forage for lichens, twigs, and dried grasses and forbs. Along the way, they mate.

Come spring, they head north to calving grounds in the Arctic Refuge. They add weight in the summer months consuming more nutritious foods -- grasses, sedges, forbs, new shrub foliage, mushrooms, and berries.

Their summer diet is essential for newborn calves. But, according to a 2007 study by Penn State researchers, higher temperatures may contribute to a mismatch between peak calf birthings and forage availability. This mismatch offers less nutrition for lactating females, threatening the health of newborn calves.

Mighty Blue Whales Confront Warming Seas

Blue whales are the giants of nature. Weighing in at 200 tons and up to 100 feet in length, they are the largest animals known to have ever lived on earth. According to National Geographic, "Their tongues alone can weigh as much as an elephant."

But, not even the mighty blue whale, already listed as endangered on the World Conservation Union (IUCN) Red List, can avoid the growing threat of global warming.

In summer months, blue whales patrol feeding grounds near the Arctic and Antarctic oceans gorging on huge quantities of krill, up to four tons a day. When blue whales migrate to their winter breeding grounds near the tropics, they live mostly off stored fat.

Global warming threatens to deliver a gut shot to blue whales. Melting glaciers and permafrost are flooding oceans with fresh water, decreasing salinity levels. That and warmer seas could shift krill location and abundance, threatening the blue whales' main food source.

Migratory Birds

Northern Oriole

Migratory birds already face a complex set of challenges, surviving and navigating long distances between their wintering and breeding grounds, often with shocking precision.

The migrant life will only become more complex, however, with climate change.

Migration timing is key to reproductive success and survival, and the migratory cycle is intricately timed to correspond with seasonal events -- like weather, bud break, and insect cycles -- that are affected by climate change.

Researchers have already observed that global warming is most likely triggering earlier spring migration and nesting. For some species, there is a risk of insect and nesting cycles falling out of synch, meaning less food available to fast-growing nestlings.

Futhermore, the ranges of many birds wintering in North America appear to be shifting northward as winter temperatures increase, according to a 2009 report recently released by the National Audubon Society.

EDF is working to improve the outlook for migratory bird populations by improving habitat on farms and ranches across the country where birds nest and rest on migration, and through our legislative work on Farm Bill conservation programs and endangered species policy.