A splendid fairy (left) attempts to evade the cuckoo
David Ongley
More than 20 bird species globally utilize similar “whining” alarm calls to alert others about the presence of cuckoos. These calls seem to resonate across species, shedding light on their evolutionary significance.
Cuckoos are among the numerous 100 species recognized as brood parasites, laying their eggs in the nests of other birds and relying on them to raise their young as if they were their own.
Will Feeney and his team at biological stations in Spain and Doñana identified 21 species that last shared a common ancestor around 53 million years ago. These species exhibit structurally similar “whimper” calls when they detect a breeding parasite.
Examples include the splendid fairy-wren (Malurus cyaneus) in Australia, the yellow-brown prinia (Prinia subflava) in Africa, Hume’s leaf warbler (Phylloscopus humei) in Asia, and the green warbler (Phylloscopus trochiloides) in Europe.
“It seems these diverse bird species worldwide have converged on the same vocalization to alert against their respective brood parasites,” observes Feeney.
Researchers often observe that species producing this alarm call tend to inhabit areas rich in brood parasites, which exploit various host species. When a potential host detects the whining, they often resort to aggressive defense behaviors.
“Brood parasites present a unique threat. They pose significant risks to offspring while largely being non-threatening to adult birds,” says Feeney. “Our findings suggest that [the call] plays a crucial role in promptly alerting fellow birds and potentially securing their protection.”
“In the case of the splendid fairy-wren, they are cooperative breeders, which likely means that the mobbing call is intended to attract additional individuals for support,” explains Rose Thorogood from the University of Helsinki, Finland.
To deepen their investigation, Feeney and colleagues recorded calls from brood-parasite hosts across continents and played them to potential host birds in Australia and China. They discovered that hearing foreign alarm calls prompted just as quick a response as calls from their own species.
“This indicates that the function of this vocalization is geared towards fostering interspecies communication rather than merely internal signaling,” highlights Feeney.
Thorogood cautions: “The ancestral alarm calls shared by our forebears may not have solely targeted brood parasites. Instead, they likely feature specific acoustic properties that are effective in repelling these threats.”
The research team also conducted similar experiments with yellow warblers (Setophaga petechia) in North America, which serve as egg hosts for brown-headed cowbirds (Molothrus ater) yet do not produce the distinctive whining alarm call. When exposed to the splendid fairy-wren’s alarm, warblers responded promptly by returning to their nests, demonstrating distress through various calls in addition to mobbing.
Feeney suggests that numerous bird species respond to innate components in alarm calls, while local birds in areas where brood parasites are prevalent adapt their calls and responses to convey information about local dangers.
“These birds have adapted distress calls for new contexts related to offspring threats,” he explains. “This provides insights into why birds across the globe utilize similar sounds.”
Charles Darwin proposed in his 1871 work, The Descent of Man, that spoken language’s origins could be traced back to imitation and adaptation of instinctual sounds made by humans and other animals. These instances may not only involve cries of fear but can also reflect pain. “A bird adapting these instinctual calls for different purposes might represent a foundational step towards language,” concludes Feeney.
Rob Magrath of the Australian National University notes, “Calls often convey specific meanings, sometimes referring to external objects or incidents, rather than merely indicating internal states like fear or traits such as gender or species.”
“This referential quality suggests that such vocalizations bear resemblance to human language, frequently referencing the external world,” he adds. “Thus, animal communication and human language may exist on a continuum rather than being distinct attributes of humans.”
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Source: www.newscientist.com
