Chirping, whistling, chirping,… Birds have a whole repertoire for expressing themselves and exchanging with their congeners. But not all of them have the same sound language. Each species is distinguished by particular cries and songs which can also vary according to regions and individuals.
Unfortunately for the regent honeyeater, a passerine bird native to Australia, this “sound culture” could become history. This is according to a study published in the journal Proceedings of the Royal Society B by researchers from the Australian National University and BirdLife Australia.
According to this work, the species-specific song Anthochaera phrygia would be disappearing. The reason: its very small population. The bird would indeed have become so rare that young individuals would no longer be able to learn their characteristic vocalizations.
A critically endangered species
The Regent Honeyeater is a medium-sized passerine bird recognizable by its mostly black plumage dotted with yellow spots and bands. Endemic to Australia, it evolves mainly in the eucalyptus forests of the south-east of the continent but it has become considerably rare in recent years.
While the population was previously estimated at 1,500 mature individuals, it now amounts to only some 300 birds in the wild, including perhaps 150 males. And the species is listed as critically endangered by the International Union for Conservation of Nature (IUCN).
It was while searching for the regent honeyeater that researchers began to take an interest in its song. “They are so rare and the range they can occupy is so vast – it was like looking for a needle in a haystack.“, told the BBC Dr. Ross Crates, lead author of the study.
During this research, he found that some birds “sang strange songs“.”It looked nothing like a regent honeyeater. They sounded like different species“, he clarified.
Very different songs
In order to learn more, scientists collected all sightings of the species recorded between July 2015 and December 2019 to assess the distribution and density of wild populations. They then went into the field to record the vocalizations of several dozen males.
At the same time, they also captured the songs of captive specimens and collected old recordings of wild males dated from 1986 to 2011. Verdict: the team highlighted clear differences between the vocalizations of all individuals. In particular among those evolving in the less dense populations.
Where the A.phrygia were relatively numerous, the males emitted rich and complex songs specific to their regions. Some, on the other hand, showed atypical, similar but abbreviated vocalizations. Others emitted completely different songs, imitating those of other species.
“Some were songs one would expect from a droplet honeyeater or a screeching polochion“, decrypted Dr. Crates for ABC. “Some were wacky… The birds were singing like an omnicolor parakeet or a big alarm clock”. According to the study, 18 males were affected, or 12% of the total population.
Looking at these specimens, the researchers found that all of them were in areas of very low population. For their part, the captive individuals emitted completely different songs from the rest of the subjects studied.
In lack of learning
As humans learn to speak, many birds learn to sing through the intervention of older specimens of the same species. However, in young regent honeyeaters, this process is increasingly compromised due to population decline.
“When young birds leave the nest and soar out into the big world, they need to associate with other, older males so they can listen to them sing and repeat their song over time.“, indicated Dr. Crates. Except that today, some fail to find congeners to serve as their teacher.
“These juveniles then end up learning the songs of other species.“, he continued. “If this species begins to lose its sonic culture, we fear this could be a dangerous red flag that it is literally on the brink of extinction.“, he lamented.
Because it is not a question of a simple question of vocalizations. This disappearance directly influences the behavior and survival of the regent honeyeaters. The results suggested that specimens with songs slightly or completely different from the norm were less likely to find a mate and reproduce.
“Many songbirds, including the regent honeyeater, use their song to impress females“, recalled the Australian researcher. Except that with atypical vocalizations, it would be much more difficult for males to communicate with their congeners and to attract a possible partner.
Singing lessons in captivity
Scientists fear that this loss of “sound culture” will exacerbate the bird’s decline. According to them, this would be the first time that such an inability to communicate with its own species has been documented in a wild animal. “Our study demonstrates that a major decline erodes culture in a wild animal population“, they write in their report.
If the discovery seems alarming, researchers have found a way to help the Australian passerine bird. A reintroduction program for specimens born in captivity has already been set up at Taronga Zoo in Sydney to boost populations. The idea is to teach the young the song of their species before they are released.
“We use our recordings of good singing males that we have found in the wild over the past five years, and play them through loudspeakers to young birds in captivity.“, detailed Dr. Crates for ABC. With the hope that they learn it and then make good use of it.
“We hope that […] if they sing well, it will make them more attractive to females when released into the wild“, he concluded.
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