Idiom:
Lose your marbles ( go crazy )

Hit the book:
The experiments by some scientists tell us that bats use the sunset to calibrate the Earth's magnetic field for use as a compass. But the story may be still more complicated. In birds, it's not the sun itself that is responsible for this calibration, but the polarised light it creates in the atmosphere as it sets.

While GPS tracking is widely used on birds, it is much rarer on bats, partly because most bats are too small to carry even lightweight devices. However, Yossi and Ivo have arrived with GPS trackers weighing just 3 grams - the lightest ever built.

The trouble with these devices is we need to recapture the same bat in order to recover the data. But we have recovered 19 of 24 of these devices so far, and although the data are preliminary, they are also exciting. Soon we may know as much about bat navigation as we do about how birds find their way around. In essence we'll no longer be in the dark about the way these fascinating animals navigate.