Birds may have revealed an instinctive yet learned language, giving scientists new clues into how communication evolves across species.
What makes this bird call unique?
A new study, published in Nature Ecology and Evolution, describes an animal vocalisation with both instinctive and learned elements. Scientists investigated the superb fairy-wren in Australia, which makes a distinctive sound when it encounters a brood parasite like a cuckoo. When other birds observe this sound, they attack the intruder, demonstrating the sound conveys essential information.
Brood parasites put eggs in other birds' nests and compel the host to raise their chicks. Cost to host species is high, so this is an ideal system for the study of evolution in the field. Birds worldwide seem to produce similar calls exclusively towards brood parasites, suggesting a shared method of communication across species.
How widespread is this call among birds?
Researchers analysed online wildlife databases and identified 21 species making the same call towards brood parasites, including cuckoos and parasitic finches. Some species are closely related and live nearby, but others diverged over 50 million years ago and inhabit different continents. This indicates that the call is not limited by geography or ancestry.
Experiments in Australia showed fairy-wrens and white-browed scrubwrens produced the call when presented with taxidermied cuckoos, but rarely with other predators. Playback experiments established that birds reacted strongly to the calls even when made by novel species. The results indicate this vocalisation is being used to transmit across species to alert to a shared threat.
What does this tell us about language origins?
While responding to the call appears instinctive, producing it is learned by observation. Juvenile birds develop the call after seeing adults produce it near a brood parasite. This combination of instinctive response and learned production represents a midpoint between typical animal vocalisations and human language.
Scientists say that the new findings bolster Charles Darwin's theory that employing instinctive sounds in novel situations could have given rise to language. By examining birds' common "universal" calls, researchers learn about the evolutionary milestones spanning animal communication and human language.
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