…The miniature backpacks were developed by Mark Johnson and Peter Teglberg Madsen at Aarhus University in Denmark. Weighing about 3g, they included instruments that recorded altitude, acceleration and sound. The team placed the backpacks in party balloons to protect them, and used medical glue to stick them to bats, which weigh 40-60g. The bats, which were using roosting boxes that were regularly monitored, had already been fitted with tiny microchips to monitor their comings and goings…