Tiny, monkeylike creatures called tarsiers sing duets together in the style of opera singers — but those who fail to hit the high notes may also flop at attracting mates, scientists recently suggested.
With their large, pointed ears and expressive eyes, nocturnal tarsiers carry a striking resemblance to the diminutive Jedi master Yoda from "Star Wars" films. But while Yoda never demonstrated any operatic ability, tarsiers are energetic singers who may exert themselves vocally as a form of sexual selection or to signal to each other that it's time for all members of a troop to gather together to sleep, according to a new study.
To learn more about these vocal performances, scientists eavesdropped on tarsiers in Tangkoko National Park in Sulawesi, Indonesia in July and August 2018, and captured 50 recordings of 14 pairs of Gursky’s spectral tarsiers (Tarsius spectrumgurskyae) singing their morning duets. Researchers from Sam Ratulangi University in Sulawesi and Cornell University in Ithaca, New York, used machine learning to distinguish and classify notes and musical phrases in the tarsiers' songs. Their findings, published Aug. 2 in the journal Frontiers in Ecology and Evolution, suggest that these performances are so taxing that not all tarsiers can hit the fast and high notes and duet proficiently.
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Measuring just 3.5 to 6 inches (9 to 15 centimeters) tall and weighing no more than 7 ounces (200 grams), Gursky’s spectral tarsiers live only on Sulawesi, an Indonesian island east of Borneo. They were described as a separate species from other tarsiers in 2017 and are classified as vulnerable by the International Union for the Conservation of Nature's (IUCN) Red List of Threatened Species. About 13 species of tarsiers inhabit islands in Southeast Asia.
The researchers captured the tarsiers' duets using a handheld digital recorder and autonomous recording devices that were installed in the tarsiers' jungle habitats. "Tarsiers are one of the easier duetting primates to record and study, at least in Tangkoko National Park, as they have small home ranges and seem to duet most mornings," said senior study author Dena Clink, a researcher at Cornell’s K. Lisa Yang Center for Conservation Bioacoustics. "They are not afraid of humans, so we were able to get high-quality recordings relatively easily."
When the scientists analyzed the intricate duets, which were performed between male and female tarsiers, they found that the performances resembled coloratura — a singing style that produces many notes very rapidly and that’s used by opera singers during arias to showcase their control and virtuosity.
"The duets exhibit acoustic trade-offs in note rate and note bandwidth — the range of frequencies within a note," said Isabel Comella, lead study author and a researcher at the K. Lisa Yang Center. The tarsiers that sing more slowly do so with the widest range of frequencies within a note, while the tarsiers that repeat notes more quickly only appear capable of a narrower range of frequencies within a note, Comella told Live Science in an email. Only a minority manage both simultaneously. The authors hypothesize that rapidly singing notes containing a broad range of frequencies during a duet may be more physiologically and neurologically taxing for the singer, with only physically fit individuals able to do so.
Exactly why tarsiers duet in such a complex and physically taxing way is unknown, largely because the animals are rarely studied. Other primates are known to sing duets, including a type of lemur called the indri (Indri indri), titi monkeys in the Callicebus genus, and northern gray gibbons (Hylobates funereus), according to the authors. Prior studies into primate duets suggest that this behavior may be used for finding or guarding a mate, defending territory or strengthening social bonds, though further research is required to determine exactly why tarsiers are performing these duets, the study authors reported.
However, one possibility for the Sulawesi tarsiers is that their duetting could be linked to organization of their social groups. Tarsiers often forage alone at night for insects, and then reunite in the morning to sleep, and they may sing together at night "as a way to bring all group members to the same sleep tree," a function that is not seen in other duetting primates, Comella said.
It could be a unique behavior to the tarsiers in Sulawesi, according to the authors. Tarsiers in the Philippines and Borneo are more solitary and don’t engage in duets as regularly.
Though Gursky’s spectral tarsiers sing their duets in the range of human hearing, the primates also vocalize in the ultrasonic range, which researchers are currently investigating. “We hope that with the advent of low-cost autonomous recording units and even smartphones we can start to learn more about the vocal behavior of tarsiers across Sulawesi," Clink said.
Originally published on Live Science.
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