Patience may be a virtue, but Tilda, a female orangutan currently living in a German Zoo, would rather not wait to receive attention, and has started producing human-like vocalizations in order to be noticed by her keepers. That makes Tilda the first known wild-born orangutan to produce novel calls similar to those made by humans. Furthermore, her intriguing ability may help us understand more about the evolutionary origins of speech, which continues to elude researchers.
Tilda was born in the wild in Borneo around 50 years ago, but was captured when she was about two. Although there are no records for her between the ages of two and ten, it is believed that she may have been trained for human entertainment. That’s because she exhibits numerous human-like behaviors which are never observed in the wild, such as clapping, arm-waving and whistling, alongside her unique vocalizations. It’s thought that she may have first learned these calls and behaviors by copying humans, but she now produces them without prompting.
In order to understand what might be motivating Tilda to produce these calls, researchers from the University of Amsterdam made video recordings of her behavior at Cologne Zoo, Germany. As described in PLOS ONE, they found that she could produce two distinct calls at a speech-like rhythm, which were dubbed “clicks” and “faux-speech.” Neither of these had been documented previously in orangutans, but both demonstrated similarities to human speech.
For the former, Tilda produces different tones by clicking her tongue, much like how humans produce voiceless consonants. For the latter, she makes grumbles in a similar manner to how humans produce vowels, Discovery News reports. Although orangutans are known to be able to produce both voiceless calls, such as kiss-sounds and raspberries, and voiced calls, such as long vocalizations, none of these have demonstrated rapid lip movements like the clicks and faux-speech.
It didn’t take the research team long to figure out why she might be making these vocalizations: to acquire food. They deduced that they were likely communicative signals because she only produced the calls when her keepers were around, and when she was directly facing them during feeding time. Furthermore, she often pointed at the food in the caretaker’s hand with her lip or index finger whilst making the vocalizations.
Alongside impressing us with her unique abilities, these findings are important because they may ultimately shed light on the origins and evolution of human speech. According to the publication, realizing how consonant- and vowel-like calls are used in both the wild and captivity could help further our knowledge of the conditions that brought together the two basic building blocks of speech. Moreover, Tilda’s calls hint that the common ancestor of great apes was able to both learn and produce human-like calls.
Although Tilda’s calls are distinct to any other known rhythmic calls described in orangutans, other intriguing vocalizations have been documented in the past. Bonnie, another female orangutan currently residing at the National Zoo in DC, taught herself to whistle seemingly just for pleasure. According to linguistics expert Mark Sicoli, this indicates that whistling would have been in the range of potential sound-making behavior of Archaic humans, including Neanderthals.