Warbler with Geolocator Backpack (IMAGE) Penn State Caption The research team placed geolocators, essentially small backpacks with light sensors, on the birds' backs, allowing the researchers to approximate location of birds along their migration track and at their wintering grounds. Credit Gunnar Kramer Usage Restrictions Credit must be provided alongside image. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.