Using state-of-the art recording technology, Ramsier and colleagues in the field have conducted key onsite research with the elusive Philippine tarsier, a small and endangered primate. Recordings made so far indicate that the tarsier’s vocalizations may represent a “private channel” of communication via ultrasonic signals. They are undetectable either by the human ear or by many of the monkey’s prey and predators.
Ramsier expects further research and analysis to determine what advantages the tarsier derives from its specialized sensory adaptation. But the evidence she and her colleagues at other institutions have collected to date on the Philippine islands have broader implications for all vertebrates.
That is because comparatively few mammals send and receive pure ultrasonic signal.
As Ramsier writes in a new paper she has co-authored for the journal of Biology Letters of London’s distinguished Royal Society (founded 1660), major advances in non-intrusive recording technology now enable researchers to generate audiograms of wild animals without compromising their way of life or habitat. Ramsier and her colleagues expect future research to provide insights into the basic attributes that would promote high-frequency hearing in all vertebrates.
The joint paper published by the Royal Society, “Primate Communication in the Pure Ultrasound,” states that although the particular advantages of the tarsier’s specialized sensory adaptation are uncertain, additional studies will compare the evolutionary, behavioral and physiological foundations of ultrasonic communication.
Believed to have inhabited rainforests for some 45 million years, the tarsier is found on several islands of the southeastern part of the Philippine archipelago. It is hard for scientists to spot the small monkey, only about three to six inches in height. Its disproportionately large eyes—the largest relative to body size of any mammal—are fixed in their sockets. But the specially-adapted neck enables the tarsier to turn its head a full 180 degrees. Its name derives from its elongated “tarsus,” or ankle bone.
The tarsier’s large, membranous ears are in constant motion and Ramsier cautions eco-tourists and other observers that the quasi-silent whirr of some cameras, for example, may be extremely loud and startling to a creature whose super-sensitive hearing is coupled with a capacity for ultrasonic vocalization.
Anthropologists confront both practical and technical limitations to studying the tarsier’s sensory faculties, especially its hearing. The primate is rare, endangered and, Ramsier says, nearly impossible to maintain in captivity. However, her research indicates that the primate can hear as well as transmit ultrasounds. She and her partners recorded the vocalizations and hearing of wild tarsiers on three islands. Both their upper limit of hearing and their ultrasonic calls are among the highest values recorded for terrestrial mammals “and an extreme example of acoustic communication.”
More online
Hear an interview with Researcher Marissa Ramsier at CBC Radio-Canada
Ramsier’s Royal Society paper is posted at http://rsbl.royalsocietypublishing.org/lookup/doi/10.1098/rsbl.2011.1149.
Visit the Royal Society online at royalsociety.org.