The Argentine parrot (Myiopsitta monachus) is a species of the Psittacidae family (parrots or parrots) that has become an invasive species and pest in many regions far from its native territory in Argentina, Brazil, Bolivia, Uruguay and Paraguay. Barcelona is an example of the adaptive capacity of these parakeets with bright green plumage and noisy activity. Indeed, to the ears of neighbors and tourists, Argentine parrots (like the very similar, although of different origin, Kramer's parrots, Psittacula krameri) make noises. For experts, that is, from a scientific point of view, however, it is not noises but songs, calls and even vocalizations that these birds emit.
There is data on the presence of wild Argentine parrots in Barcelona for almost 50 years and during the last two decades a monitoring program directed by the Museu de Ciències Naturals de Barcelona has been marking and following the individualized behavior of some 3,000 of these birds.
The Barcelona experience is the basis of a study led by experts from the Max Planck Institute of Animal Behavior in Radolfzell (Germany) and the Museu de Ciències Naturals de Barcelona in which evidence is presented, for the first time, that individuals of this Species have a unique tone of voice, known as a vocal print, similar (except for differences) to that of humans. "This finding in a wild parrot raises the possibility that a voice print may also be present in other vocally flexible species, such as dolphins and bats," the authors indicate in an article presenting their results published in the journal Royal Society Open Science.
"It makes sense that these birds have an underlying voiceprint," says Simeon Smeele, leader of the Cultural and Cognitive Ecology research group at the Max Planck Institute in Radolfzell and first author of the now published scientific paper. "It's an elegant solution for a bird that dynamically changes its calls but still needs to be recognized individually in a very noisy flock."
Humans have complex and flexible vocal repertoires, but we can still recognize ourselves with our voices alone. This is because humans have a voice print: our vocal tract leaves a unique signature in the tone of our voice in everything we say, the authors explain in a note released jointly by the Max Planck Institute and the Museu de Ciències. Naturals.
Other social animals also use vocal signals to be recognized. In birds, bats, and dolphins, for example, individuals have a unique "characteristic call" that makes them identifiable to group members. But signature calls encode identity into a single type of call. To date, there is almost no evidence that animals have unique signatures underlying all calls made by an individual. In other words, almost no animal has a voice print.
The absence of data on these voice prints in other species surprised Simeon Q. Smeele, who had already begun studies on communication skills in several species. Among the data prior to his specific study with parrots in Barcelona, Smeele recalls that, in previous studies, it has been proven that parrots, similar to humans, use their tongue and mouth to modulate calls, which means that " "Its growls and screeches sound much more human than the clean whistle of a songbird."
Additionally, like humans, parrots live in large groups with diverse and changing members. "There could be dozens of birds vocalizing at the same time," he says. "They need a way to keep track of which individual makes which sound."
Smeele wondered if parrots, possessing the right anatomy along with the need to navigate complex social lives, might have evolved vocal imprints as well. To find out, she traveled to Barcelona, where the largest population of individually marked parrots exists in the wild. Argentine parakeets (Myiopsitta monachus) swarm through the city's parks and gardens in flocks of hundreds of birds and the monitoring program run by the Museu de Ciències Naturals de Barcelona has valuable data on them.
Armed with shotgun microphones, Smeele and his colleagues recorded the calls of hundreds of individuals, collecting 5,599 vocalizations, including 3,203 contact calls, 185 tja calls, 265 truup calls, 249 alarm calls, and 364 growls; , making it the largest study of individually marked wild parrots to date. Importantly, Smeele re-recorded the same individuals over two years, revealing how stable the calls were over time.
They then used a set of models to detect how recognizable individuals were within each of the five main types of calls given by this species. Surprisingly, they found great variability in the so-called "contact call" that birds use to convey their identity. This overturned a long-standing assumption that contact calls contain a stable individual signal and suggested that budgerigars are using something else for individual recognition.
To test whether voiceprints were at play, Smeele turned to a machine learning model widely used in human voice recognition, which detects the identity of the speaker using the tone of their voice. They trained the model to recognize individual parrot calls classified as "tonal" in sound.
Once the model was trained on an individual, they tested to see if the model could detect the same individual from a different set of calls that were classified as "grunts" in sound. The model was able to do this three times better than expected by chance, providing evidence that monk parakeets have a voice print, which Smeele said "could allow individuals to recognize each other no matter what they say."
The authors caution that the evidence is still preliminary. "Before we can talk about a true voiceprint, we need to confirm that the model can repeat this result when trained with more data from more individuals, and that birds can also recognize this timbre in vocalizations," says Smeele.
The Barcelona team would complement future experiments and analyzes with an ecological study, tagging the parrots with GPS devices to determine how many individuals overlap in their roaming areas.
"This may provide information about the species' remarkable ability to discriminate between calls from different individuals," says Juan Carlos Senar of the Museu de Ciències Naturals de Barcelona.
And if it turns out that conures have a real voice print, Smeele believes this would provide an answer to the question of how these birds can be so vocally flexible and sociable at the same time. The implications would also go beyond parrots: "I hope that this finding will spur more work to discover voice prints in other social animals that can flexibly modify their vocalization, such as dolphins and bats," highlights the lead author of this study on animal behavior.
