Wiping out the world's mass migrations

Jun 01, 2009
These are pronghorn (Antilocapra americana) running in snow. Image: J. Berger/WCS

Densely packed wildebeests flowing over the Serengeti, bison teeming across the Northern Plains—these iconic images extend from Hollywood epics to the popular imagination. But the fact is, all of the world's large-scale terrestrial migrations have been severely reduced and a quarter of the migrating species are suspected to no longer migrate at all because of human changes to the landscape. A recently published research paper highlights this global change and presents the first analysis of the dwindling mass migrations.

" science has done a poor job in understanding how migrations work, and as a result many migrations have gone extinct," says Grant Harris of the Center for and Conservation at the American Museum of Natural History, first author of the paper in Endangered Research. "Fencing, for example, blocks migratory routes and reduces migrant's access to forage and water. Migrations can then stop, or be shortened, and animal numbers plummet."

Migrations of large-bodied herbivores (also called ungulates) occur when animals search for higher quality or more abundant food. Ecologically, there are two primary drivers of food availability. In temperate regions of the world, higher-quality food shifts predictably as the seasons change, and animals respond by moving along well-established routes. For savannah ecosystems, rain and fire allow higher-quality food to grow. This is a less predictable change that animals must track across expansive landscapes.

Human activity now prevents large groups of ungulates from following their food. Fencing, farming, and water restrictions have changed the landscape and over-harvesting of the animals themselves has played a role in reducing the number of migrants.

To assess the impact of human activity on migrations throughout the world, Harris and his co-authors gathered information on all 24 species of large (over 20 kilograms) ungulates known for their mass migrations. Animals included in the study, for example, range over Arctic tundra (Caribou), Eurasian steppes and plateaus (Chiru and Saiga), North American plains (bison and elk), and African savannahs (zebra and wildebeests). The fewest number of mass-migrating species live in the Americas, and this is the location where the most data exists. Evaluating the human impact on migratory species in Africa and Eurasia is hampered by a lack of scientific data: in Africa—where most of the large-scale migrations remain—three species have no scientific publications on their status, and in Eurasia half of the six remaining migratory species are very poorly documented.

All 24 species in the current study lost routes and were reduced in number of individuals. In North America, bison are still considered migratory, but their range is now restricted from the Great Plains to two small sites in Yellowstone and Alberta. Similar changes are found on other continents when human activity limits the ability of species to move to new patches of food. The analysis found even more drastic curbing for six species in particular. The springbok (Antidorcas marsupialis), black wildebeest (Connochaetes gnou), the blesbok (Damaliscus dorcas), and quagga (Equus quagga) of southern Africa; the kulan (Equus hemionus) of central Asia; and scimitar horned oryx (Oryx dammah) of northern Africa either no longer migrate or are impossible to evaluate as migratory animals.

"If we are going to conserve migrations and species, we need to identify what needs to be done: where migrations remain, how far animals move, their habitat needs and location, threats, and the knowledge gaps needed to be filled," says co-author Joel Berger of the Wildlife Conservation Society and the University of Montana. "For some of these species, such as the wildebeest and eland in Botswana, threats were identified decades ago. We as a society have made little progress at figuring out how to save migrations."

"A large part of this is an awareness issue. People don't realize what we have and are losing," says Harris. "We lose migrations and become biologically depauperate with farms and fences, even though there is no reason why humanity cannot technically and socially advance while maintaining natural phenomena. A balance can be struck—we just need to strike it."

Source: American Museum of Natural History

Explore further: From dandruff to deep sea vents, an ecologically hyper-diverse fungus

add to favorites email to friend print save as pdf

Related Stories

Study of guanacos launched in Chile

Jun 10, 2008

The Wildlife Conservation Society has launched a study in Chile's Karukinka reserve on Tierra del Fuego to help protect the guanaco – a wild cousin of the llama that once roamed in vast herds from the Andean ...

Is it too late to save the great migrations?

Jul 29, 2008

Long gone are the days when hundreds of thousands of bison grazed the Great Plains, millions of passenger pigeons darkened the skies while migrating to and from their breeding grounds, and some 12.5 trillion Rocky Mountain ...

Bison can thrive again, study says

Apr 29, 2008

Bison can repopulate large areas from Alaska to Mexico over the next 100 years provided a series of conservation and restoration measures are taken, according to continental assessment of this iconic species ...

Should Humans Give Overheated Species a Lift?

Jan 24, 2007

As the Earth warms up (2006 was the hottest year on record in America and the hottest in Britain since 1659), ecologists expect many plants and animals to move up, too -- up north and uphill, to locations where temperatures ...

National Zoo scimitar-horned oryx going into the wild

Mar 04, 2008

A male scimitar-horned oryx from the Smithsonian’s National Zoo’s Conservation and Research Center in Front Royal, Va., is playing an important role in ensuring the species does not vanish from the planet.

Recommended for you

Speckled beetle key to saving crops in Ethiopia

9 hours ago

(Phys.org) —An invasive weed poses a serious and frightening threat to farming families in Ethiopia, but scientists from a Virginia Tech-led program have unleashed a new weapon in the fight against hunger: ...

New tool to assess noise impact on marine mammals

9 hours ago

A new desktop tool which will allow offshore renewable energy developers to assess the likely impacts of their projects on marine mammal populations has been developed by scientists at the University of St ...

Of bees, mites, and viruses

Aug 21, 2014

Honeybee colonies are dying at alarming rates worldwide. A variety of factors have been proposed to explain their decline, but the exact cause—and how bees can be saved—remains unclear. An article published on August ...

User comments : 0