THREE ANCIENT RIVER SYSTEM CREATED VIABLE ROUTES FOR HUMAN MIGRATION

Three ancient river systems, now buried, may have created viable routes for human migration across the Sahara to the Mediterranean region about 100,000 years ago, according to research published September 11 in the open access journal PLOS ONE by Tom Coulthard from the University of Hull, UK, and colleagues from other institutions.

Simulating paleoclimates in the region, the researchers found quantitative evidence of three major river systems that likely existed in North Africa 130,000-100,000 years ago, but are now largely buried by dune systems in the desert. When flowing, these rivers likely provided fertile habitats for animals and vegetation, creating 'green corridors' across the region. At least one river system is estimated to have been 100 km wide and largely perennial. The Irharhar river, westernmost of the three identified, may represent a likely route of human migration across the region. In addition to rivers, the researchers' simulations predict massive lagoons and wetlands in northeast Libya, some of which span over 70,000-square kilometers.

"It's exciting to think that 100,000 years ago there were three huge rivers forcing their way across a 1000km of the Sahara desert to the Mediterranean -- and that our ancestors could have walked alongside them" said Coulthard.

Previous studies have shown that people travelled across the Saharan mountains toward more fertile Mediterranean regions, but when, where and how they did so is a subject of debate. Existing evidence supports the possibilities of a single trans-Saharan migration, many migrations along one route, or multiple migrations along several different routes. The existence of 'green corridors' that provided water and food resources were likely critical to these events, but their location and the amount of water they carried is not known. The simulations provided in this study aim to quantify the probability that these routes may have been viable for human migration across the region.

ELEPHANTS FEARS TIGERS

Wild Asian elephants slink quietly away at the sound of a growling tiger, but trumpet and growl before retreating from leopard growls, researchers at the University of California, Davis, have found. The work, published Sept. 11 in the journal Biology Letters, could help Indian farmers protect their crops from marauding elephants and save the lives of both people and animals.

"We noticed that the elephants were more scared of tigers than of leopards," said Vivek Thuppil, who carried out the work with Richard Coss, professor of psychology at UC Davis, as part of his Ph.D. in animal behavior.

Thuppil and Coss studied the elephants' behavior in an effort to prevent conflicts between human farmers and elephant herds that raid their fields by night. It's the first study of nighttime antipredator behavior in elephants.

Crop raiding by elephants is a serious problem in India, Thuppil said. Farmers use drums, firecrackers and electrified fences to try to keep them out of their crops. About 400 people a year are killed during these encounters, and some hundred elephants are killed through poisoning, electrocution or other means, according to an Indian government report.

The researchers set up equipment to play back leopard or tiger growls triggered when the elephants crossed infrared beams across paths leading to crop fields, and captured the events on video.

Leopards aren't known to prey on elephants, but tigers will sometimes attack a young elephant that becomes separated from the herd.

Although their initial reactions were very different, the elephants ultimately retreated from growls of both cats.

The elephants might be confused by the leopard growl, Thuppil said. A real leopard would most likely retreat from a group of elephants. Still, there's probably no benefit to the elephants in risking an encounter with a leopard, even if it is not a known predator.

"You don't want to mess with something with claws and teeth," Thuppil said.

"They're acting in a very intelligent way," Coss said.

Wild elephant populations are stable or even increasing in forest areas, Thuppil said. While the forest itself is protected, human settlement increasingly has moved into the buffer areas surrounding the forest, which elephants pass through while foraging or visiting different patches of forest.