5 Epic Animal Migrations Under Threat From Human Roadblocks
As seasons change, countless animal species instinctively know it’s time to get on the move—to travel from feeding grounds to breeding grounds. Those two locations can be half a world apart, but an obstacle like distance can’t stop nature’s migrating marvels. Yet we can. From creating superhighways to setting mile-long fishing nets, people increasingly block the natural pathways of animals.
Here’s a look at five animals that brave incredibly long journeys every year, and the obstacles they face.
For the 1.4 million blue wildebeests in East Africa, their lifelong journey really is the “circle of life.” Starting in January, the herd congregates on the fringes of the Serengeti’s southern shortgrass plains and begins an epic 1,500-mile clockwise migration through the national parks of Kenya and Tanzania. Zebras and gazelles join the wildebeests in their annual migration—exhibiting a true “herd mentality” as the animals chase the rainy season that brings water and greener pastures.
Apart from crocodile-infested rivers, hungry lions, and human hunters, the world’s largest mammal migration could find its way blocked by a new threat: roads. A planned Serengeti highway would connect human populations west of Lake Victoria with populations east of the national parks, but it could also disrupt the animals’ travel corridors. Fences to keep the animals off the highway could stop them from reaching vital food and water sources.
The monarch butterfly migration is a family affair—actually more of a generational pursuit. Starting in the mountains of central Mexico, millions of butterflies head north, sometimes traveling as far as 3,000 miles to Canada, breeding along the way. Each butterfly only lives for about three months, so by the end of spring a second generation is born. By the end of August, the great-great-grandchildren of the Mexican migrants start the long journey back south for the winter. No one is quite sure how, but the instinctive insects have been known to return to the same tree their relatives inhabited the previous winter.
The number of monarch butterflies making the annual migration to Mexico has dropped from around a billion in the 1990s to just 56 million this year.
Illegal logging in Mexico has eliminated some wintering sites, while severe weather has affected migrations. But the biggest factor in the monarch population crash has been the widespread and growing use of herbicides in the United States’ farm belt, which has eliminated much of the milkweed that the butterflies depend on for food. The U.S. Fish and Wildlife Service is reviewing a petition to protect the butterfly under the Endangered Species Act.
Humpback whales are the kings of mammal migration, typically traveling between 2,500 and 4,000 miles. Some whales go as far as 5,160 miles from Costa Rica to Antarctica. The species lives in all of the world’s oceans, and populations make regular journeys along both coasts of the U.S., traveling from Alaska to Mexico in the Pacific Ocean and from Newfoundland to the West Indies in the Atlantic. Swimming between winter calving grounds and summer feeding spots, the whales almost never rest, traveling at a slow, steady pace of one to six miles per hour.
The marine mammals can become entangled in abandoned fishing nets and lines, while those migrating through shipping lanes risk deadly collisions with cargo vessels or cruise ships.
Barn swallows, robins, warblers, and other songbird species spend their summers in the temperate regions of Europe before heading to their South African wintering grounds some 6,000 miles away. They can travel up to 200 miles a day and typically flock in large numbers on their journey south.
On top of crossing the Sahara Desert, during which many birds face starvation and exhaustion, new challenges are leading to declines in multiple migrating songbird species. Climate change is confusing birds about when to migrate, with some species leaving too early or too late, and industrial agriculture is reducing food supplies for many birds.
Illegal songbird trapping is also on the rise. On a British military base on the island of Cyprus—a stopover point for many birds traveling from northern Europe to Africa—more than 900,000 songbirds were killed in a single autumn migration season. The birds has long been used in a traditional dish called ambelopoulia, though trapping was outlawed in 1974.
Poachers string long, near invisible nets between trees and then play recorded birdsongs to attract robins, warblers, and orioles. Since 2002, more than 150 species of songbirds have been trapped in Cyprus. Conservation organizations are removing acacia shrubs on the base that poachers use as hideouts when trapping birds.
Caribou can be found in North America, Europe, and Siberia, but only one herd claims to hold the record for the longest migration for a land-based mammal. Alaska’s Porcupine herd, some 169,000 strong, migrates between winter and summer ranges about 400 miles apart. But the caribou's meandering route means the animals can travel 1,000 miles during their annual migration. Scientists have observed some animals migrating as far as 3,000 miles.
A portion of the Arctic National Wildlife Refuge (which includes much of the Porcupine herd’s range) has been leased for oil and gas exploration. The area, along the refuge’s northern coastal mountain range, is prime real estate for caribou. If oil and gas development were allowed on the site, it would most likely alter the animals’ migratory pattern and reduce the amount of food available during calving season. According to the Wildlife Conservation Society, just a 5 percent drop in calf survival rates would trigger a decline in the Porcupine caribou population.
President Barack Obama in January proposed closing the strip along the coast to development, which would permanently bar drilling throughout the 19.8-million–acre reserve.