A recent study by Ross Crates, a scientist at ANU’s Difficult Bird Research Group, explains why Regent Honeyeaters are changing their songs. More importantly, Ross wanted to find out what the change means for their future.
Australia’s most endangered songbird
Australia’s most threatened songbird, the Regent Honeyeater (Anthochaera (Xanthomyza) phrygia), is changing its bird call.
A changing call makes it difficult for Regent Honeyeaters to find each other and breed. It also poses a particular challenge for the researchers like Ross and his team. The inconsistency in bird call means it is difficult to research these birds and protect them.
The Regent Honeyeater was commonly found throughout Australia’s south-east, but due to land clearing since the 1960s, it is now on the verge of extinction (critically endangered in NSW and QLD, endangered in ACT and SA). The most recent data suggests there are probably less than 350 individuals remaining. This makes it more important than ever for researchers to investigate ways to protect them.
Can songs provide insights into species decline?
To address the rapid decline in species numbers, Ross and his team are looking into many different factors affecting Regent Honeyeater populations. These include habitat requirements, the range of Eucalyptus trees they like to feed on, and genetic analysis. He has also been listening to the honeyeater’s bird songs.
“We wanted to investigate the impact of population decline on the songs they sing, the complexity of the song and also their individual fitness,” said Ross.
“We were particularly looking at the male birds because the song is a crucial tool to attract a mate.”
Finding the data: live recordings and the back catalogue
Ross pulled together lots of Regent Honeyeater data from surveys and BirdLife Australia sightings. This data was used to assess distribution and density of the remaining wild populations. For the sound recordings of the honeyeaters’ contemporary songs, the research team recorded birds in the wild and in captivity. They then used the ALA to find historical song recordings of wild males from 1986 to 2011.
“The ALA provides access to over 5,200 sound files of bird songs. This was incredibly useful for us as we could make comparisons and work out how regent honeyeater songs have changed over time,” said Ross.
Then it was time for some easy listening – was their old stuff better than their new stuff?
How the songs of the Regent Honeyeater have changed
Ross and his team listened to and coded over 228 songs. They found the two main groups of wild birds had their own distinct songs: The Blue Mountains song and the Northern Tablelands song.
They also found that some birds within each group sang different songs. Some sang a shortened version of their group’s song, but others copied the songs of much more abundant birds, such as the Little Wattlebird, Noisy Friarbird, Spiny-cheeked Honeyeater, Pied Currawong, and Eastern Rosella.
“We found that Regent Honeyeaters were copying other birds and singing atypical songs, if their population density was low in that area. Males that sang other species’ songs had significantly fewer conspecifics (birds of the same species) living close by, than males that sang species-specific songs,” said Ross.
“We also found that birds that sang different songs were less likely to be paired with a female in that breeding season.”
Impact of this research
In this research paper, Ross’ team have come closer to understanding how animal cultures are maintained, the conditions under which they are lost, and the impact this has on both species’ evolution and conservation.
“We found rare evidence showing that a severe decline in population size and density is associated with the loss of vocal culture in a wild animal population. This is similar to the loss of human languages globally,” said Ross.
“Also, for the first time, we’ve shown that birds in very small groups in the wild suffer from significant changes that affect their fitness to reproduce. And these changes may speed up the decline in numbers.”
Changing the way we monitor endangered bird populations
By researching the endangered Regent Honeyeater and their changing songbook, Ross and his team have found that the birds are changing their songs to learn songs of more abundant species. This may be a precursor to extinction in already declining populations.
“This approach – where we monitor how birds are changing their songs – may provide a new way for assessing the trajectory of population decline, especially for species whose populations are very difficult to monitor in traditional ways,” said Ross.
For more information:
- Read the full research paper (open access): Loss of vocal culture and fitness costs in a critically endangered songbird
- Read more about the Difficult Bird Research Group