Farmer's Weekly (South Africa)
Conservation: Population crash causes rare bird to lose its song
Researchers from the Australian National University have found that in areas where there are very small populations of the critically endangered regent honeyeater, the songs of the remaining wild males vary remarkably. Tragically, in some cases, the birds have even adopted the songs of other species.
Just as humans learn languages, animals learn behaviours crucial for survival from older individuals of the same species. In this way, important ‘cultures’ such as bird songs are passed from one generation to the next.
But global biodiversity loss means that many animal populations are becoming small and sparsely distributed. This jeopardises the ability of young animals to learn important behaviours.
Nowhere is this more true than in the case of the regent honeyeater ( Anthochaera phrygia), a critically endangered, nectar-feeding songbird endemic to south-eastern Australia. A recent paper by Australian National University (ANU) scientists describes how a population crash to fewer than 300 has caused the species’ song culture to break down.
In healthy populations, the song of adult male honeyeaters is complex and long. But where the population is very small, the song is diminished and, in many cases, the birds have adopted the songs of other species. Sadly, this makes the males less attractive to females, which may increase the chance of the regent honeyeater becoming extinct.
Regent honeyeaters once flew in huge flocks between Adelaide and Queensland’s central coast, tracking eucalyptus blossoms. As recently as the 1950s, the species was a common sight in suburban Melbourne and Sydney, but it is now extremely rare in these cities.
Extensive post-war land clearing has destroyed regent honeyeater habitat and caused the population to plummet. Most breeding activity is now restricted to the Blue Mountains and Northern Tablelands in New South Wales.
These birds are most vocal during the early stages of their breeding season. Before the population decline, the birds were known for their soft, warbling song produced with characteristic head-bobbing. But a research project monitoring regent honeyeaters since 2015 has found that, with so few birds left in the wild, their song is changing, with potentially tragic consequences.
FINDING THEIR VOICE
Birdsong is a well-studied example of animal culture. Young birds learn to sing by listening to, repeating and refining the songs of older flock mates.
Song-learning is often completed in a bird’s first year of life, after which its song is ‘fixed’.
Despite the increasing number of endangered bird species, there is surprisingly little research into how declines in population size and density might damage song culture in wild birds. The ANU research sought to explore whether this link existed in regent honeyeater populations.
Males of the species sing to secure breeding territories and attract mates. During the course of the research, the songs of 146 male regent honeyeaters were classified between 2015 and 2019. Researchers also made or obtained high-quality recordings of 47 of these in the wild, and more in captivity; these included wild birds found by the general public and reported to BirdLife Australia.
The location of each male was noted and researchers tracked its breeding success. The songs of captive-bred regent honeyeaters that were part of a reintroduction programme were also recorded.
CHANGING TUNES
The research showed that the songs of remaining wild males varied significantly across regions. For example, the ‘proper’ song of regent honeyeaters occurring in the Blue Mountains west of Sydney, where most of the remaining population occurs, differs noticeably from the song of the small number of males hanging on 400km to the north, near Glen Innes. Although these males still sound like regent honeyeaters, their songs are slower and have a different melody.
Across the species’ entire range, researchers found 18 males whose songs sounded nothing like a regent honeyeater’s. Instead, they closely resembled those of other bird species. Five male regent honeyeaters had learnt the song of the little wattlebird, and four males had learnt songs of the noisy friarbird. Others sounded like pied currawongs, eastern rosellas or little friarbirds. There are isolated cases of individual songbirds mistakenly learning the song of a different species, but to find 12% of males singing only other species’ songs is unprecedented in wild animal populations.
Based on these findings, researchers think that regent honeyeaters are now so rare in the
landscape that some young males are unable to locate adult males from which to learn their song. Instead, the young males mistakenly learn the songs of different bird species they have associated with when developing their repertoires. Evidence suggests that this song behaviour is distinct from the mimicry common in some birds. Mimicry involves a bird adding the songs of other birds to its own repertoire, but not losing its original song. However, the researchers recorded some regent honeyeaters that never sang songs resembling that of their own species.
In addition, mimicry in other species has typically evolved because it increases breeding success. In regent honeyeaters, however, researchers found the opposite. Even among males that sounded like a regent honeyeater, those whose songs were unusual for the local area were less likely to impress, and be paired with, females. Females that did couple up with males with unusual songs were less likely to lay eggs.
This data suggests that the loss of song culture is associated with lower breeding success, which could be exacerbating regent honeyeater population decline.
A captive-breeding programme is a key component of the regent honeyeater recovery plan. However, research showed that the songs of captive-bred regent honeyeaters were shorter and less complex than those of their wild counterparts. This may affect the breeding success of captive-bred males once they are released to the wild. Consequently, researchers are teaching captive juveniles to sing correctly by playing them recordings of ‘proper’ songs from wild birds in the Blue Mountains.
THE HONEYEATER’S FINAL SONG?
Maintaining animal cultures in both wild and captive populations is increasingly recognised as crucial to preventing extinctions. These cultures include not just song, but also other important behaviours such as migration routes and feeding strategies.
The loss of the regent honeyeater song culture may be a final warning that the species is headed for extinction. This is an aspect of species conservation that cannot be ignored.
The researchers are calling for the urgent restoration and protection of breeding habitats, the protection of nests from predators, and the teaching of captive-bred birds to sing. Climate change, which threatens the species’ habitat, also has to be addressed. Otherwise, future generations may never hear the regent honeyeater’s dulcet tones in the wild.
• This article was written by Dr Ross Crates, Dr Dejan Stojanovic, Naomi Langmore and Prof Rob Heinsohn of the Australian National University and was first published by theconversation.com. To read the original article and listen to recordings of birdsong mentioned in this article, visit bit.ly/3vU2Pqz.
THE BIRDS ARE SO RARE THAT SOME YOUNG MALES CANNOT FIND ADULTS FROM WHICH TO LEARN THEIR SONG