Parrots Mimic Sounds, Yet They Still Recognize Each Other’s Voices — How?

Parrots, renowned for their mimicry, not only have the ability to imitate a variety of sounds but they also possess unique voices of their own, according to a new study

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Parrots are amongst the best mimics in the animal world. They have complex and flexible vocal repertoires, and they learn a variety of sounds throughout their lives. But despite their sometimes extensive vocal repertoires, these talented impressionists can still be individually recognized by members of their community by voice alone. How?

Voice prints. According to a new study, parrots may have their own unique voice print, just as people do. In humans, our voice print is created by the structure of our vocal tract, which creates a recognizable auditory signature in the tone of our voice.

Like humans, parrots use their tongue and mouth to modulate calls, meaning that “their grunts and shrieks sound much more human than a songbird’s clean whistle,” said the study’s first author, behavioral ecologist Simeon Smeele, who completed this research as part of his PhD thesis at Max Planck Institute of Animal Behavior. (Dr Smeele is now a postdoctoral fellow at Aarhus University where he is monitoring bat voices using passive acoustics.)

But humans aren’t alone in having our own special vocal signatures. Other animals, such as birds, bats and dolphins, produce a unique “signature call” that makes individuals identifiable to members of their community. But signature calls, which seem to operate similarly to a personal name, are just one call type. And in fact, until now, there was little evidence to suggest that animals have distinctive vocal signatures embedded in every sound they make.

Dr Smeele wondered whether parrots, which appear to possess the proper anatomy combined with a need to navigate and manage their complex social lives — just like humans — evolved unique voices, too? In short, do parrots have a singular voice print that underlies everything that each individual parrot says?

To test this idea, Dr Smeele travelled to Barcelona where the largest population of individually marked parrots in the world can be found. Monk parakeets, Myiopsitta monachus, are native to the grasslands of South America but, because they’re popular pets, they’ve established free-flying populations in urban areas around the world. These parrots are highly social; nesting communally by building large, multifamily stick nests in trees or on power poles. They live in flocks numbering hundreds of birds in Barcelona’s parks.

“It makes sense for monk parakeets to have an underlying voice print,” said Dr Smeele in a statement.

Additionally, Dr Smeele noted, monk parakeets are like people: they are gregarious, living in large groups with fluid membership.

“There could be tens of birds vocalizing at the same time,” Dr Smeele said. “They need a way of keeping track of which individual is making what sound.”

“It’s an elegant solution for a bird that dynamically changes its calls but still needs to be known in a very noisy flock.”

To better understand these invasive parrots, the Museu de Ciències Naturals de Barcelona has (so far) marked 3000 of these feral parakeets in Barcelona during the past 20 years, and monitors their movements. Barcelona’s tagged monk parakeet flocks provided the perfect opportunity for Dr Smeele to investigate his questions about their vocalizations.

Dr Smeele and collaborators used specialized microphones to record the calls of hundreds of individual parrots, collecting a total of 5,599 vocalizations produced by 229 marked parrots. Dr Smeele and collaborators also followed up and re-recorded the same individuals over a two year period to document how stable their calls are over time.

Dr Smeele and collaborators then analyzed these calls to detect individual recognition patterns. The team was surprised to discover that contact calls, which they thought were stable and unique for each bird, were actually highly variable. This finding suggests that the parrots are relying on another mechanism for individual recognition, was it individual voice prints?

To answer this question, Dr Smeele and collaborators used a machine learning model that recognizes the identity of individual people from the timbre of their voices, and trained this machine model to recognize individual parrots from the timbre of their voices. After training, Dr Smeele and collaborators tested the model to see if it could recognize the same individual from a group of different calls that listeners classified as “growling”. The machine model was three times better than expected by chance.

This study provides some evidence that the parrots do have individual voice prints, which Dr Smeele said “could allow individuals to recognize each other no matter what they say.”

“Before we can speak of a true voice print, we need to confirm that the model can repeat this result when it is trained with more data from more individuals, and that birds can also recognize this timbre in the vocalizations,” Dr Smeele cautioned, emphasizing the need for more comprehensive data and further validation.

Dr Smeele is already planning an ecological study where the parrots will be tagged with GPS devices to catalogue their movements and social interactions.

Dr Smeele thinks that, if monk parakeets genuinely possess individual voice prints, this could solve the conundrum of how parrots can be so vocally versatile whilst maintaining social cohesion.

“I hope that this finding prompts more work to uncover voice prints in other social animals that can flexibly modify their vocalization, such as dolphins and bats.”

Source:

Simeon Q. Smeele, Juan Carlos Senar, Lucy M. Aplin and Mary Brooke McElreath (2023). Evidence for vocal signatures and voice-prints in a wild parrot, Royal Society Open Science 10(10):230835 | doi:10.1098/rsos.230835

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