How blind mole rats find their way home.

The blind mole rat is the first animal found to navigate by combining dead reckoning with a sense of Earth's magnetic field, researchers say.

People and dogs can manage minor feats of dead reckoning, going in the right direction for at least a little ways in the dark, explains Tali Kimchi of Tel Aviv University in Israel. In mammals, this process, called path integration, relies on internal clues such as the sensations of walking. Bees and ants enhance path integration by reading the position of the sun.

The blind mole rat (Spalax ehrenbergi), native to eastern Mediterranean regions, can't rely on the sun. It lives underground in elaborate tunnel networks, where a mistake in direction can waste a lot of energy. In 2001, Kimchi and colleague Joseph Terkel showed that these animals sense Earth's magnetic field.

To see how mole rats actually use that innate magnetic compass, Kimchi and her colleagues tested the animals in different networks of tubes, one shaped like a wheel with eight spokes and another assembled as a grid. The researchers first used gates to force the mole rats to use inefficient paths to reach locations where the animals had been trained to expect food rewards. When the scientists gave the mole rats free passage throughout the networks, the animals worked out more-efficient routes.

When the scientists used electrical coils to mimic a 90 degree direction shift of Earth's magnetic field in the networks, the animals became disoriented on their longer forays for food, but not the shorter ones. That result indicates that the animals use compass navigation, in addition to dead reckoning, for their longer travels, the researchers conclude in the Jan. 27 Proceedings of the National Academy of Sciences.--S.M.