 Owl butterfly with transmitter on its back.
From the home of precision watch works now come radiotransmitters tiny enough to track insects.
Behavioral ecologist Beat Naef-Daenzer of the Swiss Ornithological Institute in Sempach and his colleagues wanted to study young barn swallows preparing to leave their nests, but no transmitter on the market fit the job. So they created their own from the smallest components available, coming up with a 200-milligram instrument capable of broadcasting over a 2-kilometer range for 3 weeks.
The researchers have now moved beyond swallows and are field-testing the instrument on owl butterflies, which weigh about 2 grams. Most animal species weigh less than 20 grams, notes Naef-Daenzer, and population movements of many are "virtually unknown because individuals cannot be tracked over more than a few minutes." He says minitransmitters could help track little creatures such as tree frogs, African locusts, or Europe's endangered aquatic warbler. The group, whose report appears in the 1 November Journal of Experimental Biology, is looking into smaller power sources, such as ultrathin polymer photovoltaic cells.
"Half of the world's birds are too small to use traditional tags for. This opens up a large set of species to do that work with,"says ornithologist David Winkler of Cornell University. CREDIT: BEAT NAEF-DAENZER | 
