Only the lonely: an endangered bird is forgetting its song as the species dies out

Shutterstock

Ross Crates, Australian National University; Dejan Stojanovic, Australian National University; Naomi Langmore, Australian National University, and Rob Heinsohn, Australian National UniversityJust as humans learn languages, animals learn behaviours crucial for survival and reproduction from older, experienced 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 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 regent honeyeaters. In a paper published today, we describe 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 song of other species. Sadly, this makes the males less attractive to females, which may increase the chance the regent honeyeater will become extinct.

A soft, warbling song

Population decline is damaging song culture in regent honeyeaters.
Murray Chambers

Since 2015, we have monitored the regent honeyeater – a critically endangered, nectar-feeding songbird. The birds once roamed in huge flocks between Adelaide and Queensland’s central coast, tracking eucalyptus blossom.

As recently as the 1950s, regent honeyeaters were a common sight in suburban Melbourne and Sydney but are now extremely rare in both cities.

Extensive postwar 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.

Regent honeyeaters 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 with few birds left in the wild, their song is changing – with potentially tragic consequences.

Finding their voice

Birdsong is one of the most well-studied examples of animal culture. Young songbirds learn to sing by listening to, repeating and refining the songs of older flockmates.

Song-learning is often completed in first year of life, after which a birds’ 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. We sought to explore whether this link existed in regent honeyeater populations.

Male regent honeyeaters sing to secure breeding territories and attract mates. We classified the songs of 146 male regent honeyeaters between 2015 and 2019. We made or obtained high-quality recordings of 47 of these in the wild, and more in captivity. This included wild birds found by the general public and reported to BirdLife Australia. We quickly chased up these public sightings to record the birds’ songs before they moved on.

We noted the location of each male and tracked its breeding success. We also recorded the songs of captive-bred regent honeyeaters that were part of a reintroduction program.

---

Read more:
Scientists used ‘fake news’ to stop predators killing endangered birds — and the result was remarkable

---

Changing tunes

Our research showed the songs of remaining wild males vary remarkably across regions. For example, listen to the “proper” song of regent honeyeaters occurring in the Blue Mountains west of Sydney, where most of the remaining population occur:

Regent honeyeater singing a ‘proper’ song.
Author provided121 KB (download)

You’ll notice they sound noticeably different to the small number of males hanging on 400km to the north, near Glen Innes. Although these males still sound like a regent honeyeater, their songs are slower and have a different melody:

Regent honeyeater singing a slower song.

Across the species’ entire range, we found 18 males whose songs sounded nothing like a regent honeyeater. Instead, they closely resembled those of other bird species. Five male regent honeyeaters had learned the song of the little wattlebird:

Regent honeyeater singing the song of the little wattlebird.

Four males had learned songs of the noisy friarbird. Others sounded like pied currawongs, eastern rosellas or little friarbirds:

Regent honeyeater singing the song of a little friarbird.

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.

We believe regent honeyeaters are now so rare in the landscape, 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’ve associated with when developing their repertoires.

Evidence suggests this song behaviour is distinct from the mimicry common in some Australian birds. Mimicry involves a bird adding the songs of other birds to its own repertoire – and so, not losing its original song. But the regent honeyeaters we recorded never sang songs that resembled that of their species.

---

Read more:
Look up! A powerful owl could be sleeping in your backyard after a night surveying kilometres of territory

---

Female regent honeyeaters avoid males with unusual songs.
Shutterstock

Also, mimicry in other species has typically evolved because it increases breeding success. However in regent honeyeaters, we 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, a female. Females that did couple up to males with unusual songs were less likely to lay eggs.

These data suggest the loss of song culture is associated with lower breeding success, which could be exacerbating regent honeyeater population decline.

A captive-breeding program is a key component of the regent honeyeater recovery plan. However our research showed the songs of captive-bred regent honeyeaters were shorter and less complex than their wild counterparts:

The song of a captive-bred regent honeyeater.

This may affect the breeding success of captive-bred males once they’re released to the wild. Consequently, we’re teaching captive juveniles to sing correctly by playing them our recordings of “proper” songs from wild birds in the Blue Mountains.

The honeyeaters’ 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 the species is headed for extinction. This is an aspect of species conservation we can’t ignore.

We must urgently restore and protect breeding habitats, protect nests from predators and teach captive-bred birds to sing. We must also address climate change, which threatens the species’ habitat. Otherwise, future generations may never hear the regent honeyeater’s dulcet tones in the wild.

---

Read more:
Birds that play with others have the biggest brains – and the same may go for humans

---

Ross Crates, Postdoctoral fellow, Australian National University; Dejan Stojanovic, Postdoctoral Fellow, Australian National University; Naomi Langmore, Research Fellow, Australian National University, and Rob Heinsohn, Professor of Evolutionary and Conservation Biology, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Advertisement

Wake up, Mr Morrison: Australia’s slack climate effort leaves our children 10 times more work to do

Dan Himbrechts/AAP

Lesley Hughes, Macquarie University; John Hewson, Crawford School of Public Policy, Australian National University; Malte Meinshausen, The University of Melbourne, and Will Steffen, Australian National UniversityThere is much at stake at the highly anticipated United Nations climate summit in Glasgow this November. There, almost 200 nations signed up to the Paris Agreement will make emissions reduction pledges as part of the international effort to avoid catastrophic climate change.

Many countries recognise the urgent task at hand. Ahead of the meeting, more than 110 governments have already pledged to achieve net-zero emissions by 2050. So where is Australia in terms of global ambition?

We, some of Australia’s most senior climate change scientists and policymakers, have come together to address these and other pressing questions, informed by sound science and policy.

Our report, released today, pinpoints the emissions reduction burden Australians will bear in future decades if our Paris targets are not increased. Alarmingly, people living in the 2030s and 2040s could be forced to reduce emissions by ten times as much as people this decade, if Australia is to keep within its 2℃ “carbon budget”.

Without policy change, people living in coming decades will have to reduce emissions by far more than the current rate.
Dean Lewins/AAP

‘Manifestly inadequate’

A “carbon budget” identifies how much carbon dioxide (CO₂) the world can emit if it’s to limit global temperature rise to internationally agreed goals. Those goals include keeping warming to well below 2℃ – and preferably below 1.5℃ – this century.

National emissions reduction targets are key to staying within a carbon budget. Australia’s target, under the Paris Agreement, is a 26-28% reduction between 2005 and 2030.

In a report released in January, we showed how that target is manifestly inadequate. To remain within its 2°C carbon budget, Australia must cut emissions by 50% between 2005 and 2030, and reach net-zero emissions by 2045.

To remain inside the 1.5°C budget, we must reduce emissions by 74% between 2005 and 2030, and reach net zero emissions by 2035.

Since that report was released, the Australian government has doubled down on its 2030 target. But Prime Minister Scott Morrison appears to be inching closer to a net-zero commitment. Last month he declared his government’s goal was “to reach net-zero emissions as soon as possible, and preferably by 2050”.

Our latest report set out to determine how the burden of emissions reduction would be spread after 2030 if Australia’s 2030 target is not increased.

---

Read more:
Scott Morrison has embraced net-zero emissions – now it’s time to walk the talk

---

The Morrison government is sticking with its inadequate Paris pledge.
Shutterstock

What we found

Our analysis used the methodology adopted by the Climate Change Authority. This statutory body was established by the Gillard Labor government in 2012, and was charged with providing independent expert policy advice.

In 2014, the authority identified the level of climate ambition required for Australia to do its fair share in the global effort. It recommended a 30% emissions reduction between 2000 and 2025, reaching 40-60% by 2030.

But the Abbott Coalition government ignored this advice. Instead, it pledged the far weaker target of 26-28% emissions reduction.

We wanted to determine what happens if Australia sticks to that inadequate target – and so delays substantive climate action until later decades.

To meet the weak Paris target, Australia need only reduce emissions by 1.2% each year from 2020 to 2030. If Australia persists with this target but still decides to stay inside the 2℃ carbon budget, that leaves just 1,329 million tonnes of greenhouse gases we can emit after 2030.

Keeping to this limit would be extremely challenging. If done in a straight-line trajectory, it would mean a 12.9% cut in emissions each year from 2030, until net-zero emissions were reached in 2037.

This represents an annual challenge ten times greater than what’s needed in each year this decade to meet the current 2030 goals. It would require an annual emissions reduction of 66.8 million tonnes of greenhouse gases – more than every car and light commercial vehicle on Australia’s roads emits in a year.

---

Author provided/The Conversation, CC BY-ND

---

Second, we looked at the emissions trajectory if Australia was to achieve net-zero emissions by 2050, while still keeping the inadequate 2030 Paris targets. We found people living in the 2030s and 2040s would have to reduce emissions by three times more than what’s required this decade.

---

Emissions include land-use, landuse change and forestry emissions. A drop in widespread land clearing creates the impression of overall reduced emissions. But underlying fossil fuel and industrial emissions have steadily increased since the 1990s – with the exception of brief moments when Australia had an effective price on carbon.
Author provided/The Conversation, CC BY-ND

---

Clearly, the inadequate 2030 target is the source of the problem. By requiring very little emissions reduction this decade, the Morrison government is kicking the climate can down the road for our children to pick up. It means Australia is also failing on its moral obligation to do its fair share in the global climate effort.

Australia trails the world

This sad state of affairs is not news to the rest of the world. Australia is widely viewed as an international climate laggard. In the 2020 Climate Change Performance Index, it received the lowest rating of 57 countries and the European Union. It also ranked second-worst on climate action, out of 177 countries, in the 2020 UN Sustainable Development Report.

The Glasgow climate summit, known as the 26th Conference of the Parties or COP26, seeks to hold governments to account for their climate pledges. Nations are expected to front up with ambitious short-term plans for emissions reduction.

Many nations have risen to the challenge. Countries to adopt a target of net-zero by 2050 include the United States, Japan, South Korea and the European Union. China will aim to achieve this target by 2060.

Even more importantly, some governments have ramped up their 2030 targets. For example the European Union will now reduce emissions by 55% and the United Kingdom by 68% – both on 1990 levels.

---

Read more:
Biden’s Senate majority doesn’t just super-charge US climate action, it blazes a trail for Australia

---

Under President Joe Biden, the US will work towards net-zero emissions by 2050.
Carolyn Kaster/AP/AAP

A critical decade

The importance of COP26 cannot be overstated. Under current global pledges, an average temperature rise of 3℃ or more is distinctly possible this century. This increases the risk of abrupt and irreversible changes in the Earth’s climate system – known as tipping points – bringing disastrous consequences for both human and natural systems.

The Morrison government is failing to protect Australia from this devastating future. It’s also ignoring a major economic opportunity that should – in a rational country – bring all sides of politics together.

Over the past decade, renewable energy costs have plummeted and significant advances have been made in electric vehicles and regenerative agriculture. This opens up vast new opportunities for Australia.

These days, few in the federal Coalition would deny climate science outright. But the government’s softer form of denial – failing to grasp the need for urgent action – will have the same tragic outcome.

---

Read more:
Against the odds, South Australia is a renewable energy powerhouse. How on Earth did they do it?

---

Lesley Hughes, Professor, Department of Biological Sciences, Macquarie University; John Hewson, Professor and Chair, Tax and Transfer Policy Institute, Crawford School of Public Policy, Australian National University; Malte Meinshausen, A/Prof., School of Earth Sciences, The University of Melbourne, and Will Steffen, Emeritus Professor, Fenner School of Environment & Society, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.