What's the first thing a hamster does when you've cleaned its cage? Heads for the food bowl and stuffs its pouches. Hamsters are notorious hoarders, there's nothing they like more than a nest full of food. But while Ariane Etienne studied the rodents behaviour, she realised that they were also able to navigate. Wondering how they returned home after a lengthy foraging trip, Etienne and a team of colleagues tested potential navigational strategies, and discovered that hamsters keep a record of the route they take, integrating the outbound path, to find the most direct route home. But as Roland Maurer explains, path integration isn't the most reliable navigational tool, because it accumulates errors that must be corrected with another sensory cue. Animals that `reset' the path integrator and correct these errors have a better chance of returning home successfully than animals that do not. Wondering whether hamsters use vision to correct this problem, the team set about tampering with the rodent's environment and found that a glimpse of their surroundings is enough to successfully reset the path integrator and send them in a homeward direction (p. 1491).
Hamsters aren't the sharpest creatures on the planet, so Maurer and Etienne knew that it would take each hamster plenty of time to familiarise itself with the `landscape' surrounding its enclosure; only then could the team begin their experiment to test the rodent's navigational skills.
First the team rotated the hamster's enclosure in the dark, so that the hamster was none the wiser about its nest's change of location relative to landmarks it had learned. Then one of a dedicated team of students wearing infrared goggles tempted the animal from its nest into the arena with a spoonfull of hazelnuts and watched the hamster's progress. Once the animal was in the arena, it followed the hazelnut treats while the tester lured it to walk in tight circles, disorienting the hamster slightly so that it no longer trusted its path integrator to tell it where home lay. Then the tester threw on the lights for a few seconds, giving the animal long enough to recognise the lay of the land, before plunging the arena back into darkness and luring the hamster off on a second leg of the trip. Finally, the animal was allowed to fill its pouches before deciding which way to head and embark on its homeward journey.
But which way would the hamster turn? Towards the position of the nest in the rotated arena and follow its path integrator, or would a glimpse of the landscape be enough to reset its path integrator and aim the hamster towards the position where the nest should lie according to the landmarks it had learned? After all `nests don't rotate in nature' says Maurer.
The hamsters headed off towards the point where the nest had lain before the scientists had spun their world around. The path integrator was reset. Even though the intrepid little venturers had only left their homes a matter of minutes before, a glimpse of the world they lived in wiped their memories of the homeward path, reset the integrator and sent them off in the direction home should have been.
- © The Company of Biologists Limited 2004