Bats are able to soar up to a mile above the ground during flight by riding late night winds and updrafts, according to a new study into the flying mammals.
Scientists already knew bats could reach such lofty heights, but until this new study by Southeastern Louisiana University they didn’t know how they soared so far up.
A group of European free-tailed bats were fitted with high-resolution GPS loggers that recorded their location every 30 seconds over three days – for six hours a night.
They found that the bats – which can fly at 84 miles per hour – largely followed the terrain they crossed but would occasionally climb to extreme heights, reaching a mile up in under 20 minutes by using vertical wind energy in the night sky.
Lead author Teague O’Mara said the movements were very efficient, with bats finding ways to ‘minimise how much energy they spend to find food each night.’
Scientists already knew bats could reach such lofty heights, but until this new study by Southeastern Louisiana University they didn’t know how they soared so far up
The team, which included researchers from the Max Plank Institute, wanted to find out how some bats could reach a mile above ground during flight without the benefit of thermal winds and air systems not available at night.
It turns out that the European free-tailed bats they studied depend on orographic uplift that happens when air is pushed up over rising terrain to help them fly high, just as birds do during the day.
But, because that’s harder to find during the cooler night, they have to rely on just the right sort of areas to reach those high altitudes.
‘We show that wind and topography can predict areas of the landscape able to support high-altitude ascents, and that bats use these locations to reach high altitudes while reducing airspeeds,’ explains O’Mara.
‘Bats then integrate wind conditions to guide high-altitude ascents, deftly exploiting vertical wind energy in the nocturnal landscape.’
O’Mara and colleagues tracked a group of bats through a landscape in northern Portugal over the course of three days – covering about six hours a night.
The data show that bats emerge just after sunset and fly constantly throughout the night before returning to roost.
They observed that the bats’ flight would typically follow the terrain they crossed, but that occasionally they would climb to extreme heights, reaching nearly a mile above ground level in less than 20 minutes.
During these high-altitude ascents, the bats would climb faster, longer, and at a lower airspeed than during more moderate ascents to around 984 feet.
Most bats descended quickly after reaching their peak elevation, resulting in a kind of rollercoaster flight path.
The researchers were surprised to discover just how predictable the bats’ high-flying ascents were across the landscape.
The data show that bats are using the same types of places – although not necessarily always the exact same locations – where the wind sweeps up a slope to carry them to high altitudes.
‘We were ready to see that these bats flew fast, so that wasn’t a surprise to us,’ O’Mara said. ‘But the fast, uplifting wind-supported flights were something our team really wasn’t looking for or prepared for.’
It turns out that the European free-tailed bats they studied depend on orographic uplift that happens when air is pushed up over rising terrain to help them fly high, just as birds do during the day
The findings show that bats are solving the problems of flight in similar ways to birds – just at night, the researchers note.
‘These free-tailed bats seem to find ways to minimise how much energy they have to spend to find food each night,’ O’Mara said.
This is an ‘incredible challenge’ for an animal that can only perceive an area between 100ft and 200ft ahead of it in any real detail.
‘It takes a lot of energy to fly up to 1,600 meters (1 mile) above the ground, and these bats have found a way to ride the wind currents up,’ said O’Mara.
O’Mara and colleagues tracked a group of bats through a landscape in northern Portugal over the course of three days – covering about six hours a night
Although the researchers already had a pretty good idea based on past work that the bats also could fly amazingly fast, they say this fast-flying ability remains ‘a bit of an unsolved problem.’
‘Their small body sizes and large, flexible wings covered in a thin membrane were assumed to prevent these really fast speeds,’ O’Mara said.
‘But it’s now clear that bats can fly incredibly fast when they choose. It’s up to us to figure out how they do that and if it can be applied to other scenarios,’ such as engineering bio-inspired high-speed and low-energy flight.
The findings have been published in the journal Current Biology.