Cheek by jowl

Fencing in wildlife from human intrusion is becoming increasingly attractive in some regions (see page R465) but there are also worries that the effects of these fences and other human activity are having a major impact on the movement of the world's most spectacular migrating species. All 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, according to new research. " 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 Center for Biodiversity and Conservation at the American Museum of Natural History, reporting in Endangered Species Research. " Fencing, for example, blocks migratory routes and reduces migrant's access to forage and water. Migrations can then stop or be shortened, and animals plummet. " Migrations of large-bodied herbivores 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 the reduction in number of migrants, the researchers report. To assess the impact of human activity on migrations throughout the world, Harris and his colleagues gathered information on all 24 species of large ungulates known for mass migrations. Animals included in the study include Arctic caribou, North American bison and elk and African zebra and wildebeests. The fewest number of mass-migrating species live in the Americas, but this is the location where most data exist. Evaluating the human impact on migratory species in Africa and Eurasia is hampered by a lack of 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, the researchers say. All 24 species in the current study lost migration routes and were reduced in number of individuals. …