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Zebra, asiatic ass migrations left in tatters

November 24, 2009

Southern Africa's plains zebras and the asiatic wild ass have been identified among animals whose migratory habits have been left in tatters.

A quarter of the world's migrating species are suspected to no longer migrate at all because of human changes to the landscape, and all of the world's large-scale terrestrial migrations have been severely reduced.

A recent research paper has presented the first analysis of dwindling mass migrations, and noted the plight of the plains zebra (Equus quagga) and the asiatic wild ass (Equus hemionus), which live in central Asia.

"Conservation 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 Centre for Biodiversity and Conservation at the American Museum of Natural History, who is lead author of the paper.

"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, known an ungulates, occur when animals search for higher quality or more abundant food.

Ecologically, there are two primary drivers of food availability. In temperate regions, higher-quality food shifts predictably as 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 these animals 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, Harris and his colleauges 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 poorly documented.

All 24 species in the current study lost migration routes and were reduced in number of individuals.

The analysis found drastic curbing for six species in particular - the plains zebra, asiatic wild ass, the springbok (Antidorcas marsupialis), black wildebeest (Connochaetes gnou), the blesbok (Damaliscus dorcas) and the scimitar horned oryx (Oryx dammah) of northern Africa.

These species 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."

Harris continues: "A large part of this is an awareness issue. People don't realise what we have and are losing. 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."

In addition to Harris and Berger, authors on the research paper include Simon Thirgood and Grant Hopcraft, of the Frankfurt Zoological Society in Tanzania; and Joris Cromsigt of the Mammal Research Institute at the Polish Academy of Sciences.

The research was supported by the John D. and Catherine T. MacArthur Foundation, the Frankfurt Zoological Society, the Wildlife Conservation Society, and the Marie Curie Transfer of Knowledge project BIORESC.



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