Bats 'surf' the winds of storms during migration 

Bats, often overshadowed by birds in discussions of long-distance migration, are now starting to be recognized for their remarkable travel feats. 

A new study by scientists at the Max Planck Institute of Animal Behavior (MPI-AB) has provided unprecedented insights into the migration strategies of common noctule bats. 

Using advanced tracking technology, the researchers discovered that these small mammals exploit storm fronts to maximize their energy efficiency during migration.

High-tech window into bat behavior

“The sensor data are amazing!” said Edward Hurme, a postdoctoral researcher at MPI-AB and the Cluster of Excellence Collective Behavior at the University of Konstanz. 

“We don’t just see the path that bats took, we also see what they experienced in the environment as they migrated. It’s this context that gives us insight into the crucial decisions that bats made during their costly and dangerous journeys.”

The team employed lightweight, intelligent tracking devices developed by MPI-AB engineers. These tags, which weighed just five percent of the bats’ body mass, recorded extensive data, including activity levels and air temperature, throughout the migration. 

The data were transmitted via a long-range network that provided coverage across Europe. 

“The tags communicate with us from wherever the bats are because they have coverage across Europe much like a cell phone network,” explained Timm Wild, who led the development of the ICARUS-TinyFoxBatt tag at MPI-AB.

Unique and variable bat migration path

The study focused on 71 common noctule bats during their spring migration, covering up to four weeks. Unlike the predictable corridors often seen in bird migrations, the noctule bats took varied routes, though all moved in a general northeast direction. 

“There is no migration corridor,” said Dina Dechmann, a senior author from MPI-AB. “We had assumed that bats were following a unified path, but we now see they are moving all over the landscape in a general northeast direction.”

The research also revealed that noctules can travel nearly 400 kilometers in a single night, a record for the species. However, their migration differs significantly from that of birds. 

“Unlike migratory birds, bats don’t gain weight in preparation for migration,” Dechmann noted. “They need to refuel every night, so their migration has a hopping pattern rather than a straight shot.”

Timing migration with weather

On some nights, the researchers observed a dramatic increase in departures, which Hurme likened to “bat fireworks.” This led the team to investigate the environmental triggers for these events. 

They discovered that bats tended to leave when air pressure dropped and temperatures rose – conditions associated with approaching storms. 

“They were riding storm fronts, using the support of warm tailwinds,” Hurme explained. The tags also showed that bats expended less energy on these nights, confirming that they harness wind support to power their flights. 

“It was known that birds use wind support during migration, and now we see that bats do too,” he added.

Implications for conservation

These findings have significant implications for bat conservation, particularly in mitigating the risks posed by wind turbines, a leading cause of bat mortality. “Before this study, we didn’t know what triggered bats to start migrating,” said Hurme. 

He expressed optimism that further research could lead to systems capable of forecasting bat migration. Such systems could help wind farms adjust operations to reduce collisions. 

“We can be stewards of bats, helping wind farms to turn off their turbines on nights when bats are streaming through. This is just a small glimpse of what we will find if we all keep working to open that black box.”

Further research is needed

Despite these breakthroughs, much remains unknown about the full migration cycle of noctule bats, which spans approximately 1,600 kilometers annually. The study’s novel tracking technology marks an important step in uncovering the complexities of their behavior. 

“We are still far from observing the complete yearly cycle of long-distance bat migration,” Hurme acknowledged. “The behavior is still a black box, but at least we have a tool that has shed some light.”

By continuing to explore these mysteries, researchers hope to deepen their understanding of bat migration, paving the way for effective conservation strategies and contributing to a broader understanding of animal migration.

The study is published in the journal Science.

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