Unveiling the Nighttime Hunters: A Quarter-Century Mystery Solved
After a quarter-century of dedicated research, scientists have finally cracked the enigma surrounding Europe's largest bat. This remarkable creature, known as the greater noctule (Nyctalus lasiopterus), has been revealed to be a stealthy predator, hunting and consuming small birds while soaring through the night sky.
An international team of researchers has uncovered the secrets of this bat's hunting prowess. Their findings, published in the prestigious journal Science, paint a vivid picture of the bats' aerial pursuits, precision attacks, and predation in complete darkness. This discovery not only challenges our understanding of bat behavior but also highlights the intricate strategies these nocturnal creatures employ to survive.
The Nighttime Migration of Songbirds
Every year, billions of songbirds embark on a perilous journey, migrating between their breeding and wintering grounds. Many of these birds choose to fly at night and high altitudes to evade daytime predators. However, this strategy comes with its own set of dangers, as bats emerge as the dominant night-time aerial predators.
Riding Along with the Bats
To study these elusive hunters, scientists effectively accompanied the greater noctule by equipping them with tiny "backpacks" containing biologgers developed at Aarhus University. These lightweight devices measured the bats' altitude, acceleration, movement, and sounds, including their echolocation calls. This innovative approach provided an unprecedented glimpse into the bats' nocturnal hunting strategies, revealing their tactics at altitudes exceeding a kilometer above the ground.
The bats' hunting strategy involves soaring high into the night sky to ambush unsuspecting birds. Unlike insects, birds cannot detect the bats' ultrasonic calls, giving them a crucial advantage. The bats' success hinges on their powerful, low-frequency echolocation calls, which enable them to detect birds from a distance. As they close in on their target, the bats unleash rapid bursts of short calls, signaling the final stage of their attack.
Daring Dives and Pursuit
The biologgers' data revealed that the bats execute daring, high-speed dives towards their prey, resembling fighter jets in combat. In two documented chases, the bats dove for 30 and 176 seconds, respectively, intensifying their flapping and tripling their acceleration while emitting attack calls. The first bat abandoned its pursuit, but the second succeeded after a nearly three-minute chase, capturing a robin near the ground.
The robin's distress was evident as it emitted 21 distress calls, followed by 23 minutes of chewing as the bat fed on it while still airborne. This was corroborated by X-ray and DNA analysis of bird wings found beneath hunting areas, confirming that the bat kills the bird with a bite, removes its wings, and uses the membrane between its hind legs as a pouch to hold and consume the prey.
Wild Maneuvers and Evasive Tactics
Assistant Professor Laura Stidsholt from the Department of Biology at Aarhus University explains the complexity of this hunting scenario. She notes that songbirds employ wild evasive maneuvers, such as loops and spirals, to escape predators like hawks during the day. Interestingly, they seem to use the same tactics against bats at night, showcasing the bats' ability to not only catch but also kill and eat their prey while in flight. This is particularly remarkable when considering the weight disparity between the bird and the bat.
A 25-Year Hypothesis Confirmed
For decades, scientists suspected that some large bat species prey on small birds during flight, thanks to the pioneering work of Spanish bat expert Carlos Ibáñez and his colleagues at the Doñana Biological Station (CSIC) in Seville. Nearly 25 years ago, Ibáñez discovered bird feathers in greater noctule droppings and spent years gathering evidence to support this hypothesis.
Ibáñez's team closely monitored this elusive forest-dwelling species using "smart" roosts equipped with antennas to detect implanted microchips in the bats. This innovative system tracked their movements, stored data, and sent real-time alerts to researchers' phones. Despite the evidence, the idea that bats could catch birds midair was met with skepticism due to the significant size difference between the bats and the birds.
Overcoming Technical Challenges
Filming these hunts proved challenging due to the darkness. Researchers experimented with various tools over the years, including roost cameras, military radar, hot-air balloons with ultrasound recorders, and GPS trackers, but struggled to develop tools light enough for the bats to carry. It was only with the development of miniature biologgers from Aarhus University that the team finally succeeded in recording a greater noctule hunting and eating a bird in flight, just as Ibáñez was nearing retirement.
Emotional Revelation and Conservation Implications
Co-author Elena Tena described the experience of hearing the recording as both thrilling and sobering. She emphasized the empathy it evoked for the prey, acknowledging that it was a part of nature. For the research team, this discovery confirmed their long-standing pursuit of knowledge. Tena admitted that she had to listen to the recording multiple times to fully comprehend the extraordinary nature of their findings.
Despite the bats' predatory nature, they pose no threat to songbird populations. The greater noctule is already extremely rare and endangered in many regions due to the loss of forest habitats. Understanding its behavior and ecology is now crucial for developing conservation and management strategies to protect this extraordinary nocturnal predator, ensuring the preservation of Europe's unique biodiversity.
