The Malabar Whistling-thrush uses UV-reflecting feathers and high-pitched whistles to be seen and heard in India’s lush and noisy forests.
By Rex Graham
The bird likes to nest in dense stands of teak, jamun, cashew and other trees on rocky ledges along India’s protected pristine streams. This habitat in places like the Pachmarhi Biosphere Reserve is also favored by the Honey Buzzard, Black Eagle, Malabar Pied Hornbill, Paradise Flycatcher and hundreds of other stunning birds.
The evolution of some birds’ songs appears to be heavily influenced by ambient acoustics. For example, the Screaming Piha has compensated for its life in dense, noisy forests by increasing the volume of its songs into the painful range. Some urban birds produce higher pitched songs than their rural counterparts, possibly to carry over low-pitched traffic noise.
The role of ambient acoustics in the evolution of bird song makes the Malabar Whistling-thrush an important test-species to researchers. Another bird that nests along noisy streams farther east in Asia, the Rufous-faced Warbler, produces even higher pitched songs in the ultrasonic range beyond the audible range of humans.
Malabar Whistling-thrush Communication
The Malabar Whistling-thrush may have another communication trick up its feathers. It’s not just a beautiful black-colored bird with a band of royal-blue feathers on its forehead, back and belly. It uses them to flash brilliant violet (to humans) in sunlight. While human eyes detect shades of red, green and blue, birds have added ultraviolet. So the whistling-thrushes feathers flash UV signals that we can’t see.
They and some parrots have microstructures in their feathers that may be involved in the UV signaling. They probably use those wavelengths in courtship displays, communications to circumvent ambient noise, or possibly other purposes.
Male Budgerigars and other parrot species use fluorescent plumage adjacent to UV-reflecting feathers to create highly contrasting colors that we can’t see. This high color contrast may be designed for the eyes of potential mates. Evolutionary biologists can only theorize that courtship signals based on UV contrast and signaling are important: more research is needed to decipher the system.
Recently, Peter Mullen, a biologist at the Alexander Koenig Zoological Research Museum in Bonn, Germany, discovered that dark-blue feathers of Whistling-thrushes (and other birds) reflect UV light.
“Bird of many more groups may see UV light than have been studied to date,” Koenig wrote in a paper in Ibis. “Although we do not know if UV phenomena play a role in visual signaling, they might be more suggestive of a signaling role than the UV reflections which only add to the overall brightness of a bird’s plumage.