By Amanda A. Taylor-Uchoa

RIO GRANDE VALLEY, TEXAS – FEB. 3, 2025 – In the lush landscapes of Venezuela, a remarkable phenomenon unfolds: wild green-rumped parrotlets engage in vocal behaviors strikingly similar to human babbling.

Led by Dr. Karl Berg, associate professor in the UTRGV School of Integrative Biological and Chemical Sciences, this research not only illuminates the complex vocal abilities of these parrots but also draws intriguing parallels to human language development.

A female nestling green-rumped parrotlet photographed at Hato Masaguaral Biological Station in the Llanos of Venezuela. Berg and Delgado’s work discovered baby parrotlets babble like human infants. (Photo by Karl S. Berg)

VOCAL BABBLING IN WILD PARROTS

The journey began with a hypothesis that parrots might exhibit a form of vocal babbling, a crucial phase in language development traditionally observed in human infants and songbirds.

In a groundbreaking study published in Proceedings of the Royal Society B: Biological Sciences, Berg and his colleagues documented that vocal babbling occurs widely in both male and female parrotlets during their nestling stage.

Through detailed audio-video recordings inside specially designed nest cavities, the team discovered that these parrot chicks produce a diverse array of sounds—much like human infants.

“Babbling ushers in spoken language, which is arguably our most unique behavior no animal has anything even close to our ability to speak,” Berg explains.

Their babbling begins around three weeks of age, coinciding with developmental milestones such as first contact calls, which his previous research showed were learned from their parents, however, babbling becomes increasingly complex in the days prior to flying from the nest.

“It was quite a surprise how the nestlings know the full repertoire of adult vocalizations by this age,” he remarked.

According to Berg, this signifies that the process the vocal development in these parrot chicks draw parallels to human language acquisition, demonstrating how environmental factors and developmental milestones influence vocal abilities.

THE IMPORTANCE OF SIBLING DYNAMICS

Berg has emphasized the crucial role of sibling dynamics in vocal learning among parrots. He observed that older siblings often exhibit remarkable nurturing of the younger ones instead of eliminating them.

“Older siblings seem to be hardwired for empathy,” he said, providing insight into parrot social structures.

This nurturing behavior fosters a supportive environment that enhances younger chicks' vocal development. As older siblings vocalize, they offer models for imitation, creating an interactive learning experience vital for early vocalization stages. The shared nest environment ensures continuous exposure to various sounds, allowing younger chicks to practice and refine their calls.

Berg said empathetic older siblings reduce stress for younger chicks, enabling vocal play and experimentation without fear.

“When siblings work together, it creates a safe space for learning,” he said.

This emotional support highlights just how important social bonds are for developing communication skills. Strong familial bonds like these might even point to deeper evolutionary strategies that promote cooperation among parrot populations.

A parrotlet at a nesting box as Berg works in the distance manning a remote control camera to capture the image. (Photo by Karl S. Berg)

THE ROLE OF CORTICOSTERONE

An essential aspect of this research is the influence of corticosteroids, specifically corticosterone, on vocal development. The team conducted experiments where nestlings received daily corticosterone supplements during the early weeks of babbling.

Surprisingly, rather than hindering vocal production, the corticosterone-treated nestlings exhibited larger and more complex vocal repertoires after the treatment period.

“We found that individuals that got the hormone developed a very large vocal repertoire. This is the first experimental demonstration that this hormone is involved in language acquisition in parrots,” he said.

This suggests that corticosteroids play a vital role in facilitating vocal learning during this critical developmental window, paralleling findings in human infants where corticosteroid influences are thought to shape early language acquisition.

“Results suggest a beneficial role of the Hypothalamic-Pituitary-Adrenal (HPA) axis in regulating the learning of conspecific vocalizations in parrotlets,” he said, underscoring potential parallels with the human brain and language development.

WORLDWIDE ATTENTION AND RECOGNITION

Professor Berg’s research has garnered significant international attention, spotlighting the intricate connections between vocal learning in parrots and the early stages of human language development.

His findings have been referenced in numerous high-profile articles, including:

• "Wild Elephants May Have Names That Other Elephants Use to Call Them" - All Things Considered, NPR, June 11, 2024
• "New Animal Dads Often Kill Their Stepchildren. These Parrots Adopt Them Instead" - Science News, May 6, 2024
• "Wild Parrot Chicks Babble Like Human Infants" - Science News, May 31, 2022
• "Vocal Babbling in a Wild Parrot Shows Life History and Endocrine Affinities with Human Infants" - Proceedings of the Royal Society B, May 9, 2022
• "Early Corticosterone Increases Vocal Complexity in a Wild Parrot" - Journal of Neuroendocrinology, January 2024

Berg's work continues to draw interest from various scientific communities, with studies featured in prominent publications like Science, Nature, and Psychology Today. Recently featured in NPR, the article noted how wild African elephants might use specific vocalizations akin to names.

“I have no doubt that they’re addressing them with these unique labels,” Berg said.

This connection further underscores the complexity of communication across species and highlights the growing recognition of animal cognition.

Berg also recently co-authored a study published in Proceedings of the National Academy of Sciences that revealed how green-rumped parrotlet stepfathers often choose to adopt their new mate's chicks instead of resorting to infanticide.

“It turns out that [this] can also be an effective strategy for getting one’s genes into the next generation,” Berg said, challenging long-standing assumptions about parental behavior in the animal kingdom.

LOOKING AHEAD

Berg has exciting news about his research.

“In December we completed our 36th consecutive season of research on parrotlets in Venezuela, work funded by grants from the National Science Foundation, the National Geographic Society and the Maxwell-Hanrahan Foundation. Fifteen thousand hours of nest video made of the last 20 years, unique color-banding of thousands of individuals and nest monitoring is allowing us to ask questions like, ‘Does a robust vocal babbling stage mean you’ll live a long life and make a lot of babies?’”  

Within this work, Berg credits the unwavering support and dedication of his wife and research partner, Soraya Delgado, UTRGV lecturer of Biology, for the aid in advancement of this research.

“As a husband-and-wife team, we have been working on the project in Venezuela for more than 20 years and her contribution cannot be underestimated, though often is,” he said.

Delgado co-authored many scientific articles published on this research and is now a Doctoral Education candidate at UTRGV specializing in math and science education.

As Berg's research advances, it deepens the understanding of avian vocalization while also shedding light on the cognitive processes that support communication. Berg believes this work is pivotal in bridging the divide between avian and human linguistics, enriching our knowledge of how language evolves across species.

Some audio-video examples of parrotlet babbling from Berg’s work can be found here Supplementary material Vocal babbling. A video on some of this research can be viewed here Karl Berg video. You can also access UTRGV’s Lab of Avian Ecology for more information here Lab of Avian Ecology.

Soraya Delgado, lecturer in Biology at UTRGV, in the Llanos of Venezuela. Delgado conducted field research in Venezuela for her M.Sc. thesis in Biology at UTRGV and has been collaborating on parrotlet research with Berg for over twenty years. (Photo by Karl S. Berg)