Melbourne, Oct 6 (The Conversation) Language is a fundamental tool that enables humans to connect and cooperate, facilitating extraordinary achievements. The ability to convey abstract concepts is often considered a defining trait that distinguishes humans from other species on Earth.
While pairing arbitrary sounds with specific meanings is prevalent in human language, it is seldom observed among other animals. However, recent studies have discovered that birds, chimpanzees, dolphins, and elephants also exhibit this ability. The mechanism by which this capability emerges is still not well understood.
Language is characterized by the widespread use of sounds that are associated with specific items through learning, but both humans and animals also produce instinctive sounds, such as a scream in response to pain. Over 150 years ago, Charles Darwin proposed that using instinctive sounds in new contexts might be a crucial step in developing language-like communication.
In a new study published in Nature Ecology and Evolution, researchers describe the first known instance of an animal vocalization that combines both instinctive and learned features—an example reminiscent of the stepping stone Darwin envisioned.
An Unusual Call for an Unusual Threat
Birds face numerous threats, but brood parasites present a unique challenge.
Brood parasites, like cuckoos, reproduce by laying their eggs in the nests of other species, tricking the unsuspecting hosts into raising their offspring. The first act of a baby cuckoo upon hatching is to eject other chicks from the nest, monopolizing the caregivers' attention and resources.
The significant cost imposed by brood parasitism makes it an ideal system for observing evolutionary processes in action.
Previous research showed that in Australia, the superb fairy-wren has developed a unique call when encountering a cuckoo. Other fairy-wrens respond to this alarm call by swiftly assembling to attack the intruding cuckoo.
During these studies, researchers noticed that other bird species responded similarly to this call, producing their own versions. Discussions with collaborators from China, India, and Sweden revealed that birds in those regions produced a similar call, directed exclusively at cuckoos.
Global Use of the Same Call
To investigate further, researchers examined online wildlife media databases, identifying 21 species that produce this call toward their brood parasites, including various cuckoos and parasitic finches. Some species were closely related and lived near each other, while others diverged over 50 million years ago and resided on different continents.
To discern whether this call was meant for intra-species communication or cross-species collaboration, researchers used a database of the world's brood parasites and hosts. They hypothesized that if the call served to communicate within a species, it would be more common among cooperative species who defend nests together. However, the data indicated that species producing this call inhabit areas with more brood parasites and host species, implying the call fosters cross-species cooperation against brood parasitism.
Defending Against a Common Threat
To test this, researchers conducted experiments in Australia. When superb fairy-wrens or white-browed scrubwrens encountered a taxidermied cuckoo, they made the call and attempted to attack. In contrast, the call was seldom made when presented with models of other predators.
Furthermore, playing recordings of the call to these birds triggered strong reactions, suggesting the call is primarily produced in response to cuckoos, and elicits predictable responses from other birds.
If this call acts as a "universal word" for brood parasites among birds, different species should respond similarly, even if they have never encountered each other. This was confirmed when calls from Australia elicited the same response from birds in China, and vice versa, indicating the call effectively conveys the presence of a brood parasite across species.
Insights into Language Origins
The study reveals that over 20 bird species worldwide, separated by more than 50 million years of evolution, use the same call when spotting their respective brood parasites.
Although these birds instinctively know how to respond to the call, previous research shows that birds unfamiliar with cuckoos do not initially produce the call but learn to do so after observing others.
This finding marks the first documented case of animal vocalizations that combine both instinctive and learned elements across species. It represents a potential transitional phase between animal communication and human language, supporting Darwin's earlier theories on language development. (The Conversation) SKY SKY
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