Dr. Nachum Ulanovsky of the Weizmann Institute and Prof. Ran Nathan and Asaf Tsoar of the Hebrew University of Jerusalem have captured live fruit bats and glued tiny GPS transmitters to their backs, then driven the bats overnight to a site some 80 kilometers away and rappelled into the bats’ caves to retrieve the transmitters after they fall off – all in the name of scientific research. In the process, the team has revealed how these bats form mental maps that they use to return to their favorite fruit trees night after night, often flying large distances and bypassing other, similar trees on the way.
Bats are famous users of hearing to navigate – finding their way around by echolocation. Echolocation is extremely useful for flitting around one’s immediate surroundings in the dark, but Ulanovsky and his collaborators suspected that the bats were making beelines for their trees using a different sense. Flying hundreds of meters up in the air at speeds of up to 60 km an hour, the bats appeared to rely on an internal, mental map of the territory below.
To test the limits of that map, the researchers first took the bats outside their normal range and released them. Then, to hide any visual landmarks the bats may have been using to steer by, they drove them some 84 km away and released some of them from the bottom of a wide erosion crater and others from the top. The bats released from the crater’s rim made their way straight back home from the distant, unfamiliar departure point. Only those that found themselves inside the crater seemed to lose their bearings (and these regained them, once they reached the rim).
It turns out that the saying “blind as a bat” doesn’t really apply to these furry flying mammals. “Birds’-eye view” might be more like it: The bats apparently watch for prominent visual landmarks – light clusters, for instance, or hills – judge their distance and mentally triangulate their positions. Ulanovsky thinks that these masters of navigation may even have further means of plotting their positions, as a back-up for times when visibility is poor. These could include the ability to sense directional sea breezes or magnetic fields.
Ulanovsky is a neurobiologist; he carried out this research together with the team of ecologists from the Hebrew University, and with scientists in Italy and Switzerland. Their findings could shed light on both bat ecology and the ways that mammals – including humans – form mental maps of large areas.
See a bat’s eye view of its flight path