Parrots are exceptionally communicative birds. They constantly learn new sounds and build up an immense vocal repertoire over the course of their lives. At the same time, their calls are so individual that each bird can be recognized by the other parrots in its flock. It is possible that these animals also have a vocal sound that is just as unique as humans. Researchers found evidence of this in experiments with monk parakeets. This raises the question of whether other animal species also have such a voice print.
We humans can recognize each other by our voices because we have a so-called voiceprint: In everything we say, subtle anatomical differences in our speech organs – including vocal cords, tongue and mouth – create a unique signature in the tone of our voice. Other social animals also recognize each other by their voice: birds, bats and dolphins, for example, have an individual “signature call” by which they recognize the members of their group. However, so far there is little evidence that animals not only have such unique call types, but also actually have individual vocal signatures.
Special laboratory animals: The monk parakeets in Barcelona
A research team led by Simeon Smeele from the Max Planck Institute for Behavioral Biology in Radolfszell has now examined this in more detail using the monk parakeet parrot species. Since parrots have extraordinary vocal abilities similar to those of us humans and also form large social groups, the researchers suspected that they would also find a voice print in these animals. “Because sometimes dozens of birds sing at the same time, they need a way to find out which individual is making which sound,” says Smeele. It is known that parrots use different types of calls for different purposes, including the so-called “contact call,” which birds use to announce their identity. It is assumed to contain a stable individual signal. However, there has been little research into how individual this and the other calls actually are.
In their study, the scientists analyzed the vocalizations of monk parakeets (Myiopsitta monachus) in the parks of Barcelona, where they live together in large flocks of hundreds of birds. They chose this population because the parrotbirds have been tagged for 20 years as part of a monitoring program for this invasive bird species. So far, 3,000 individuals have been identified. Over two years, Smeele and his team recorded the calls of the various parakeets several times using special microphones. They collected around 5,600 vocalizations, assigned them to 229 marked birds, and thus created the largest study of wild parrots to date. From their database, the researchers used statistical computer models to determine whether the individuals could be identified using the five most important call types.
First evidence of voice printing in parrot birds
In fact, they found weak individual signals in three of the calls: the “contact call,” the “alarm call,” and the “truup call,” which the parrots usually emit when a flock separates. At the same time, Smeele and his team also found that the structure of these calls varies greatly over time, surprisingly also with the “contact call”. The parakeets must therefore use another feature for individual recognition, the researchers concluded. They then used a machine learning model widely used in human voice recognition and trained it to recognize the five melodic call types of individual parrots. The model was then able to recognize the same individuals based on “growling” sounds, but with varying degrees of success depending on the data set used and the type of call.
The researchers conclude that monk parakeets could actually have an individual acoustic voice print. This would allow individuals to recognize each other, regardless of which call they use. However, the interpretation is still preliminary. “Before we can talk about a true voiceprint, we need to repeat this result with more data from more individuals,” says Smeele. In the future, his team also wants to equip the parrots in Barcelona with GPS devices to determine how much the individuals’ areas of residence overlap. If monk parakeets have a true vocal impression, this would explain how parrots can be so vocally flexible and social at the same time. “I hope that this discovery initiates further studies in other social animals that can flexibly change their voice, such as dolphins and bats,” says Smeele.
Source: Simeon Smeele (Max Planck Institute for Behavioral Biology) et al., Royal Society Open Science, doi: 10.1098/rsos.230835