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promoting conservation of biodiversity through the scientific study of tarsiers

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Tarsiers vary greatly, by species group, in the extent to which they vocalize. Eastern tarsiers, or the Tarsius tarsier-complex are, far and away, the most vocal. These tarsiers are also social, and they “sing” a complex, sexually-dimorphic “duet”, usually just before returning to their sleeping tree at dawn. The duet call of Eastern tarsiers varies regionally, and it is this variation that gave scientists the first clue that numerous cryptic species of tarsiers remained unidentified within the region. Let’s start by looking at a duet from one such population . . .

Listen to a tarsier duet from Tangkoko . . .

This is a recording of a tarsier duet from Tangkoko. The tape begins with the sound of the male, a short rhythmic chirping that gradually grows louder. The female is first heard about 10.5 seconds into the recording as a short, downward modulated, whistle. As the duet progresses, the males notes remain fairly similar to each other, relative to the female notes, which change markedly from beginning to end. Try to follow it by examining the spectrograph, below (you might need to open it in two pages).

Listen to that again, slowed down to half-speed . . .

The human ear and brain are not well-suited to hearing and interpreting the vocalizations of tarsiers, the sounds are too high and the modulations occur too quickly for us to process them well. This is the same recording, slowed down to half-speed. Thus, it is one octave lower and is twice as long. The male call still sounds like a chirp, but if you listen carefully you can hear that it is a chevron-shaped call, where pitch (or frequency) modulates rapidly down-up then up-down. The female call is now an eerie whistling sound. (FYI, the birds in the background start to sound pretty cool, too!). See the first 30 seconds of the recording in spectral form, below.

Now for something really weird, listen to that again, slowed down to one quarter speed . . .

At this speed, the sounds of the forest are truly eerie. The male tarsier call is now clearly an upwards-downwards, chevron-shaped call, and the female call is a long, mournful whistle. See the first 15 seconds of the recording in spectral form, below. And then look at a close-up of just one male note and one female note. These are taken from about 10.5 seconds into the original recording, or the point at which the female first starts to vocalize.