Millions of animals fly, swim or walk around the Earth every year. To ensure that they reach their destination, they need to perceive precise changes in environmental conditions and choose the right moment to set off on their journey. Bats, too, are influenced by environmental factors. Every spring, common noctules in southern Germany set off for their summer territories. Researchers at the Max Planck Institute for Ornithology in Radolfzell have been studying what conditions trigger this migration. They discovered that the decision to set off depends on a combination of wind speed, wind direction and air pressure. The researchers have developed a model that allows them to predict when the bats will start their migration.