Bats have a curious strategy for traveling: They surf the warm fronts of storms to fly further with less energy.
Birds aren’t the only long-distance fliers. There are bats that travel thousands of kilometers, in a behavior that is quite rare and difficult to observe.
However, recently, scientists at the Max Planck Institute analyzed 71 bats noctule during their spring migration across the European continent and managed to demystify this mysterious behavior.
The intelligent and ultra-light sensors attached to their bodies made it possible to discover the strategy used by small mammals to travel: these animals surf the warm storm fronts to fly further and with less energy.
The tracking device used in this study was developed by the engineers and weighs just 5% of the bat’s total body mass. According to , the small tag includes several sensors that record the animals’ activity levels and the temperature of the air around them.
Advanced technology also made it possible to compress the data, in a total of 1440 daily measurements, in a single 12-byte message which was transmitted over a new long-range network.
“The tags communicate with us wherever the bats are because they have coverage across Europe,” explained researcher Timm Wild, who led the development of the tag. ICARUS-TinyFoxBatt.
The team deployed the tags to nocturnal common, a bat frequently seen in Europe and one of four species known to migrate across the continent. Throughout the spring, over three years, scientists attached tags mostly to females because they are more migratory than males.
The technology revealed much more variable trajectories than what scientists thought. “There is no migration corridor. We had assumed that the bats were following a unified path, but now we see that they are moving across the landscape in a general northeast direction,” said researcher Dina Dechmann.
After separating the data to distinguish hour-long feeding flights from much longer migratory flights, the team found that bats can migrate nearly 250 miles in a single night. Their migratory flights were often interspersed with stops, probably because the animals needed to feed.
“Unlike migratory birds, bats do not gain weight during their preparation for migration. They need to be refilled every night, so your migration has a pattern of jumps instead of a direct shot”, added the expert.
On some nights, “we observed an explosion of departures that looked like bat fireworks,” waves of migration that could be explained by changes in climate.
The animals tended to break down on nights when the air pressure dropped and the temperature rose, i.e. before the approaching storms. “They surf storm fronts, using the support of warm tail winds,” explained Edward Hurme.
The sensors that measured activity levels also showed that the bats used less energy flying on those warm windy nights, which confirms the strategy of these small mammals to harvest invisible energy from the environment to fuel their continental flights.
The was recently published in Science.
