BioEd Online

Tiny radar devices have revealed patterns in the meandering flights of butterflies: the looping dives are thought to help them to search for food or a home. What's more, the radar technology could help conservationists to find safe havens for the insects amid fragmented agricultural landscapes.

Researchers attached radio transponders, each weighing just 12 milligrams, to butterflies and used them to track around 30 of the insects. "You have to carefully remove the hairs from their back first," explains Lizzie Cant of Rothamsted Research in Hertfordshire, UK. "I give them a wax with Sellotape."

After checking that the transponders did not affect the butterflies' behaviour, Cant and her colleagues released them into a field that was being scanned by radar. When a transponder receives a radar pulse, it sends out a characteristic reply signal that the researchers use to track the butterfly. Similar technology drives collision-warning systems on aircraft.

Loopy behaviour

The small tortoiseshell (Aglais urticae) and peacock varieties (Inachis io) that Cant studied showed two distinct flight patterns: straight movement, in which they zipped over the ground at more than 3 metres per second, and longer, slower passages in which they flew in loops. The butterflies also appeared to react to features as far as 200 metres away, for example, by altering their course to investigate a group of flowers.

Such patterns have been spotted before, although they have never been documented in the detail provided by the radar technique. Visual observations become difficult at distances of greater than 50 metres, but the Rothamsted team was able to follow the butterflies for more than a kilometre. They report their results in Proceedings of the Royal Society of London¹.

"The looping flight is thought to be a searching behaviour," says Cant. She carried out the experiments in late summer, so the insects were probably looking for nectar from flowers, or a dry place, such as a crack in a tree, in which to hibernate. Straighter flights probably occur when the butterfly wants to leave an area or escape a predator, Cant adds.

She now wants to repeat the experiment on rarer species such as the high brown fritillary (Argynnis adippe) and marsh fritillary (Euphydryas aurinia). Both are endangered and conservationists are unsure how easily the insects will be able to move between neighbouring habitats that can support them. "If we know how mobile they are, we can tell if the fragmentation is all right," she says.