Can birds hear with their feathers?
Susanne Hoffmann awarded prestigious Human Frontier Science Program (HFSP) grant to find out.
How does the oilbird, a chicken-sized, cave-dwelling bird from South America, navigate in pitch darkness using sounds it cannot even hear? This paradox has puzzled biologists for more than seventy years. Now Susanne Hoffmann, Research Group Leader at the Max Planck Institute for Biological Intelligence, and Adriana Maldonado-Chaparro, Professor at the University of Rosario in Colombia, aim to finally shed some light on this question. They suspect that oilbirds feel the vibrations of sound with the help of hair-like feathers surrounding the oilbird's beak, and have been awarded a prestigious HFSP Research Grant to explore this hypothesis.
Some animals, such as bats, navigate by echolocation. They produce sounds and listen to the echoes that bounce back from nearby objects to build a picture of their surroundings. The oilbird is one of just a few bird species also known to echolocate, and is able to avoid collisions with obstacles as small as 20 centimetres in size. But unlike any other known echolocating animal, the oilbird’s echolocation signals and hearing range do not match: the birds’ hearing is tuned to low frequencies, while their echolocation clicks are far higher in frequency than their ears are sensitive to.
The idea that feathers surrounding the birds’ beaks – known as rictal bristles – might act as sound sensors first struck Hoffmann while giving a lecture to students, describing how seals can hunt in complete darkness by tracking the underwater wake of prey with their facial whiskers. She wondered if the oilbird’s rictal bristles could work in a comparable way, not by detecting water movement, but the vibrations of airborne sound. The bristle’s follicles inside the facial skin are surrounded by vibration-sensitive mechanoreceptors in unusually high density, making them plausible candidates for detecting incoming echoes.
Specifically designed to fund new international collaborations that tackle bold research questions, the HFSP Research Grant is a perfect fit for a project that could only succeed by bringing together two researchers with wildly different research backgrounds. Hoffmann, a neuroscientist by training, searched for a collaborator working with oilbirds and found Maldonado-Chaparro, a behavioral ecologist thought to be the only researcher in the world actively doing so. Working together at cave sites in Antioquia, Colombia, the team will combine wireless neurophysiology with behavioral experiments to test their hypothesis and map the brain circuits involved in the oilbird’s echolocation behavior.
“The oilbird is something of a sensory goldmine, possessing the most sensitive visual system amongst vertebrates, using smell to locate food in the night, and being able to navigate by echolocation,” said Hoffmann.
“Demonstrating that a non-auditory mechanism for sound sensing exists could open an entirely new direction in sensory neuroscience, with possible practical applications for everything from hearing aid technology to drone navigation.”
[AG]
