Bats Soar: Harnessing Storm Winds for Epic Journeys

Traditionally, bat migration has appeared somewhat enigmatic. Although researchers have discovered much about avian migration, the limited number of bat species that undertake extensive travels have proven more challenging to observe.

“They’re swift and nocturnal,” mentions Edward Hurme, a scientist at the Max Planck Institute for Animal Behavior located in Germany. “Once they vanish from one area, we don’t necessarily possess the means to determine where they reappear elsewhere.”

Bats are also less hefty than many migrating birds, implying that the style of tracking devices which scientists attach to birds is too cumbersome for bats.

“Finding a device that can send data about an animal remotely while being small enough for a bat is quite a challenge,” states Hurme.

Consequently, Hurme and his team had to invent one. They developed specialized trackers weighing just over a gram that monitored the animal’s movements along with temperature. Unlike some other devices that record animal activity but must be collected by researchers to access the data, these innovative trackers transmit their information to a wireless network, akin to how mobile phones operate. This enables the scientists to triangulate their locations and observe the bats’ travels.

Overall, the group outfitted 71 female noctule bats with these sensors. In spring, females generally migrate from their hibernation zones in Switzerland and Germany toward the northeast, where they roost. When the researchers correlated their tracking findings with climate data, they detected an intriguing correlation.

“We discovered that many bats actually begin migrating before storms occur,” Hurme explains. In spring, storms are usually preceded by warm fronts that create strong winds blowing in the favorable direction for migration. This results in considerable energy conservation for the bats, Hurme notes, which can travel nearly 1000 miles.

Interestingly, these noctule bats time their spring departures to align with warm fronts arriving ahead of storms, Hurme and his team disclosed this week in the journal Science. Such winds typically blow in the general northeastern path of the bats’ migration during this period, providing the bats — which weigh about an ounce — a substantial boost.

“This was genuinely a major surprise. We had some indication that bats responded to favorable wind conditions, but we never anticipated that there would be this connection to storms,” remarks Hurme.

“At times they can ride the winds for one or two nights, but generally, the storm progresses through the day. So while the bats are resting, the storm continues. Then they must wait for the next suitable opportunity to migrate,” explains Hurme.

However, there is a downside to delayed departures. Many of these females are expecting, and the longer they hold off, the heavier they will become. Additionally, wind patterns can shift unexpectedly.

“By the end of the previous year, the last bat to migrate was a week behind everyone else,” says Hurme. “Yet, the wind changed direction to blow south, and eventually, it simply succumbed and migrated against the winds.”

The researchers have yet to ascertain what indicators the bats utilize to time their takeoffs. More broadly, Hurme aspires for additional research teams to commence employing the compact bat tags on various bat species.

“We’re collaborating with partners from Spain to the Czech Republic, attempting to bridge the knowledge gaps about bat activities throughout the entire region as they migrate north in the spring and return south in the autumn.”

Ultimately, such endeavors could aid in bat conservation. Collisions with wind turbines, for example, result in numerous bat fatalities. Gaining insights into when and where they migrate could assist researchers in formulating bat migration forecasts, which could help energy companies shut down turbines during migration periods or avoid constructing structures in specific locales altogether, he asserts.

“We have a significant journey ahead, but ideally, we can begin progressing toward a more accurate system for predicting precisely when and where bats will be migrating.”

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