Fruit bats use inner navigation system
Our dependence on global positioning system (GPS) technology keeps growing; we use it to help us navigate and to facilitate our travels. Many animals, however, need to navigate a landscape for survival rather than for ease. Researchers from Israel, Italy and Switzerland investigated bat navigation to determine how free-ranging mammals find their way around their natural environment. The findings of the study are published in the journal Proceedings of the National Academy of Sciences (PNAS). Scientists attached small GPS devices to Egyptian fruit bats (Rousettus aegyptiacus) to determine how they locate individual trees night after night. These bats fly many kilometres each night to feed on specific fruit trees, and return home that same night. Bats, according to the researchers, carry around an internal, cognitive map of their home range, based on visual landmarks including hills and lights. They add, however, that these creatures have an extra, large-scale navigational mechanism. Past studies have demonstrated the navigational skills of other animals such as turtles, lobsters and birds. But mammalian navigation studies were only performed in the laboratory, because such tests could not duplicate the extensive and complex landscapes an animal must navigate in the natural world. Miniaturised GPS devices, developed by researchers at the Hebrew University of Jerusalem, the Weizmann Institute in Israel, Ornis Italica in Italy and the Swiss Federal Institute of Technology (ETH) Zurich in Switzerland, contain very small GPS receivers, memory loggers and batteries. Each device weighs around 10 grams. The team used the devices to track the Egyptian fruit bats over a number of consecutive nights. Data was collated as the bats took flight each night from an Israeli cave. With speeds of 40 km per hour, the bats flew in a straight line and rose to heights of hundreds of metres to trees that were between 12 km and 25 km from their cave. All bats returned to the same trees each night; they also bypassed identical trees that were nearer to home. The researchers say the bats' navigational abilities rival those of homing pigeons. Smell is not a navigational aid, since the bats bypassed the identical trees, according to the researchers, who added that data analysis suggested that the bats were not simply using any visual or other individual cue as a beacon. A number of the bats were moved to a new desert area, 44 km south of their normal range. After releasing the first group, the bats navigated to their preferred fruit trees and returned to their cave without a hitch. The bats that were fed first just returned to the cave once they were released. The team says that based on a spatial model analysis, as well as following discussions with pilots, it seems that the bats could be using visual landmarks like lights to help them navigate. Even when the researchers moved the bats even further from their normal area, the creatures still returned to their cave despite wandering for some time and experiencing some disorientation. The researchers believe the bats use visual information from a 'bird's-eye view' to build a cognitive map of a wide area. According to them, the bats probably compute their own location by using a form of triangulation based on the various azimuths to known distant landmarks. This research study shed new light on how mammals like fruit bats use these maps to navigate in areas that are 100 km in size.For more information, please visit:Hebrew University of Jerusalem:http://www.huji.ac.il/huji/eng/PNAS:http://www.pnas.org/
Countries
Switzerland, Israel, Italy