The link below is to a news report of a Cassowary killing its owner in the USA.
The highly unusual “semi-identical” Australian twins reported last week are the result of a rare event. It’s thought the brother and sister (who have identical genes from their mother but not their father) developed from an egg fertilised by two different sperm at the same moment.
In humans, it’s the sperm that determines whether an embryo is pushed along a male or female development pathway. But in birds, it’s the other way around. Eggs are the deciding factor in bird sex.
There are other fascinating aspects of bird sex that are not shared with humans. Female birds seem to have some capacity to control the sex of their chicks. And occasionally a bird that is female on one side and male on the other is produced – as in recent reports of this cardinal in the United States.
X and Y, Z and W chromosomes
So what is it about bird chromosomes that makes bird sex so different from human sex?
In humans, cells in females have two copies of a large, gene-rich chromosome called X. Male cells have one X, and a tiny Y chromosome.
Birds also have sex chromosomes, but they act in completely the opposite way. Male birds have two copies of a large, gene-rich chromosome called Z, and females have a single Z and a W chromosome. The tiny W chromosome is all that is left of an original Z, which degenerated over time, much like the human Y.
When cells in the bird ovary undergo the special kind of division (called “meiosis”) that produces eggs with just one set of chromosomes, each egg cell receives either a Z or a W.
Fertilisation with a sperm (all of which bear a Z) produces ZZ male or ZW female chicks.
Birds can control the sex of their chicks
We would expect that, during meiosis, random separation of Z and W should result in half the chicks being male and half female, but birds are tricky. Somehow the female is able to manipulate whether the Z or W chromosome gets into an egg.
Most bird species produce more males than females on average. Some birds, such as kestrels, produce different sex ratios at different times of the year and others respond to environmental conditions or the female’s body condition. For example, when times are tough for zebra finches, more females are produced. Some birds, such as the kookaburra, contrive usually to hatch a male chick first, then a female one.
Why would a bird manipulate the sex of her chicks? We think she is optimising the likelihood of her offspring mating and rearing young (so ensuring the continuation of her genes into future generations).
It makes sense for females in poor condition to hatch more female chicks, because weak male chicks are unlikely to surmount the rigours of courtship and reproduction.
How does the female do it? There is some evidence she can bias the sex ratio by controlling hormones, particularly progesterone.
How male and female birds develop
In humans, we know it’s a gene on the Y chromosome called SRY that kickstarts the development of a testis in the embryo. The embryonic testis makes testosterone, and testosterone pushes the development of male characteristics like genitals, hair and voice.
But in birds a completely different gene (called DMRT1) on the Z but not the W seems to determine sex of an embryo.
In a ZZ embryo, the two copies of DMRT1 induce a ridge of cells (the gonad precursor) to develop into a testis, which produces testosterone; a male bird develops. In a ZW female embryo, the single copy of DMRT1 permits the gonad to develop into an ovary, which makes estrogen and other related hormones; a female bird results.
This kind of sex determination is known as “gene dosage”.
It’s the difference in the number of sex genes that determines sex. Surprisingly, this mechanism is more common in vertebrates than the familiar mammalian system (in which the presence or absence of a Y chromosome bearing the SRY gene determines sex).
Unlike mammals, we never see birds with differences in Z and W chromosome number; there seems to be no bird equivalent to XO women with just a single X chromosome, and men with XXY chromosomes. It may be that such changes are lethal in birds.
Birds that are half-male, half-female
Very occasionally a bird is found with one side male, the other female. The recently sighted cardinal has red male plumage on the right, and beige (female) feathers on the left.
One famous chicken is male on the right and female on the left, with spectacular differences in plumage, comb and fatness.
The most likely origin of such rare mixed animals (called “chimaeras”) is from fusion of separate ZZ and ZW embryos, or from double fertilisation of an abnormal ZW egg.
But why is there such clear 50:50 physical demarcation in half-and-half birds? The protein produced by the sex determining gene DMRT1, as well as sex hormones, travels around the body in the blood so should affect both sides.
There must be another biological pathway, something else on sex chromosomes that fixes sex in the two sides of the body and interprets the same genetic and hormone signals differently.
What genes specify sex differences birds?
Birds may show spectacular sex differences in appearance (such as size, plumage, colour) and behaviour (such as singing). Think of the peacock’s splendid tail, much admired by drab peahens.
You might think the Z chromosome would be a good place for exorbitant male colour genes, and that the W would be a handy place for egg genes. But the W chromosome seems to have no specifically female genes.
Studies of the whole peacock genome show that the genes responsible for the spectacular tail feathers are scattered all over the genome. So they are probably regulated by male and female hormones, and only indirectly the result of sex chromosomes.
This is part of a major series called Advancing Australia, in which leading academics examine the key issues facing Australia in the lead-up to the 2019 federal election and beyond. Read the other pieces in the series here.
We need nature. It gives us inspiration, health, resources, life. But we are losing it. Extinction is the most acute and irreversible manifestation of this loss.
Australian species have suffered at a disproportionate rate. Far more mammal species have become extinct in Australia than in any other country over the past 200 years.
The thylacine is the most recognised and mourned of our lost species, but the lesser bilby has gone, so too the pig-footed bandicoot, the Toolache wallaby, the white-footed rabbit-rat, along with many other mammals that lived only in Australia. The paradise parrot has joined them, the robust white-eye, the King Island emu, the Christmas Island forest skink, the southern gastric-brooding frog, the Phillip Island glory pea, and at least another 100 species that were part of the fabric of this land, part of what made Australia distinctive.
And that’s just the tally for known extinctions. Many more have been lost without ever being named. Still others hover in the graveyard – we’re not sure whether they linger or are gone.
The losses continue: three Australian vertebrate species became extinct in the past decade. Most of the factors that caused the losses remain unchecked, and new threats are appearing, intensifying, expanding. Many species persist only in slivers of their former range and in a fraction of their previous abundance, and the long-established momentum of their decline will soon take them over the brink.
These losses need not have happened. Almost all were predictable and preventable. They represent failures in our duty of care, legislation, policy and management. They give witness to, and warn us about, the malaise of our land and waters.
How do we staunch the wound and maintain Australia’s wildlife? It’s a problem with many facets and no single solution. Here we provide ten recommendations, based on an underlying recognition that more extinctions will be inevitable unless we treat nature as part of the essence of this country, rather than as a dispensable tangent, an economic externality.
We should commit to preventing any more extinctions. As a society, we need to treat our nature with more respect – our plants and animals have lived in this place for hundreds of thousands, often millions, of years. They are integral to this country. We should not deny them their existence.
We should craft an intergenerational social contract. We have been gifted an extraordinary nature. We have an obligation to pass to following generations a world as full of wonder, beauty and diversity as our generation has inherited.
We should highlight our respect for, and obligation to, nature in our constitution, just as that fusty document could be refreshed and some of its deficiencies redressed through the Uluru Statement from the Heart. Those drafting the blueprint for the way our country is governed gave little or no heed to its nature. A constitution is more than a simple administrative rule book. Countries such as Ecuador, Palau and Bhutan have constitutions that commit to caring for their natural legacy and recognise that society and nature are interdependent.
We should build a generation-scale funding commitment and long-term vision to escape the fickle, futile, three-year cycle of contested government funding. Environmental challenges in Australia are deeply ingrained and longstanding, and the conservation response and its resourcing need to be implemented on a scale of decades.
As Paul Keating stated in his landmark Redfern speech, we should all see Australia through Aboriginal eyes – more deeply feel the way the country’s heart beats; become part of the land; fit into the landscape. This can happen through teaching curricula, through reverting to Indigenous names for landmarks, through reinvigorating Indigenous land management, and through pervasive cultural respect.
We need to live within our environmental limits – constraining the use of water, soil and other natural resources to levels that are sustainable, restraining population growth and setting a positive example to the world in our efforts to minimise climate change.
We need to celebrate and learn from our successes. There are now many examples of how good management and investments can help threatened species recover. We are capable of reversing our mismanagement.
Funding to prevent extinctions is woefully inadequate, of course, and needs to be increased. The budgeting is opaque, but the Australian government spends about A$200 million a year on the conservation of threatened species, about 10% of what the US government outlays for its own threatened species. Understandably, our American counterparts are more successful. For context, Australians spend about A$4 billion a year caring for pet cats.
Environmental law needs strengthening. Too much is discretionary and enforcement is patchy. We suggest tightening the accountability for environmental failures, including extinction. Should species die out, formal inquests should be mandatory to learn the necessary lessons and make systemic improvements.
We need to enhance our environmental research, management and monitoring capability. Many threatened species remain poorly known and most are not adequately monitored. This makes it is hard to measure progress in response to management, or the speed of their collapse towards extinction.
Extinction is not inevitable. It is a failure, potentially even a crime – a theft from the future that is entirely preventable. We can and should prevent extinctions, and safeguard and celebrate the diversity of Australian life.
John Woinarski, Professor (conservation biology), Charles Darwin University; Sarah Legge, Professor, Australian National University, and Stephen Garnett, Professor of Conservation and Sustainable Livelihoods, Charles Darwin University
Nearly 20 years ago, Australia adopted national environmental legislation that was celebrated widely as a balanced response to Australia’s threatened species crisis. In the same year, Queensland introduced its Vegetation Management Act. Together, these laws were meant to help prevent further extinctions.
But have they worked?
A famous finch
We investigated whether these laws had successfully protected the habitat of the endangered southern black-throated finch.
Our study found that, despite being nominally protected under federal environmental law, habitat for the species has continued to be cleared. Just three out of 775 development applications that potentially impacted the endangered southern black-throated finch were knocked back, according to our new research.
Defining exactly what is habitat for the black-throated finch is tricky – we don’t have oodles of data on their habitat use over time, and the extent of their sightings has declined substantially. But Queensland has excellent vegetation mapping, and we recorded all of the vegetation types in which the southern black-throated finch has been seen.
We then mapped the extent of this habitat in three different time periods: historically; at the advent of the environmental laws (2000); and current day.
We found that most of the black-throated finch’s habitat had been cleared before 2000, mainly for agriculture before the mid-1970s. The black-throated finch hasn’t been reliably seen in New South Wales since 1994 and is listed there as “presumed extinct”.
We looked at all the development proposals since 2000 that were referred to the federal government due to their potential impact on threatened species. 775 of these development proposals overlapped areas of potential habitat for the black-throated finch.
Only one of these projects – a housing development near Townsville – was refused approval because it was deemed to have a “clearly unacceptable” impact to the black-throated finch.
In addition to these projects, over half a million hectares of the cleared habitat were not even assessed under federal environmental laws.
We estimate that the species remains in just 12% of its original range. Yet despite this, our study shows that the habitat clearing is still being approved within the little that is left.
So in theory, Australia’s and Queensland’s laws protect endangered species habitat. But in practice, a lot has been lost.
The highest-profile development proposal to impinge on black-throated finch habitat loss is Adani’s Carmichael coalmine and rail project. Adani has been given approval to clear or otherwise impact more than 16,000 hectares of black-throated finch habitat, a third of which Adani deemed “critical habitat” But there are four other mines in the Galilee Basin that have approved the clearing of more than 29,000 ha in total of black-throated finch habitat.
But it’s not just the mines. In 2018 the federal government approved clearing of black-throated finch habitat for a housing estate and a sugar cane farm, both near Townsville. Several solar farms have also been proposed that would clear black-throated finch habitat around Townsville.
To further complicate matters, the black-throated finch’s habitat is also threatened with degradation by cattle grazing. The finch needs year-round access to certain grass seeds, so where grazing has removed the seeding part of the grasses, made the ground too hard, or caused the proliferation of introduced grasses such as buffel, the habitat suitability can decrease until it is no longer able to support black-throated finches.
So while they are losing their high-quality habitat to development, a lot of their habitat is being degraded elsewhere.
The federal government has placed conditions on approved clearing of black-throated finch habitat, often including “offsetting” of any habitat loss. But securing one part of the black-throated finch’s habitat in exchange for losing another still means there is less habitat. This is particularly problematic when the lost habitat is of very high quality, as is the case for Adani’s Carmichael coalmine lease.
Little by little
Our research suggests there is a real danger of the black-throated finch suffering extinction by a thousand cuts – or perhaps 775 cuts, in this case. Each new development approval may have a relatively modest impact in isolation, but the cumulative effect can be devastating. This may explain why a stronger environmental response has not occurred so far.
So how can we prevent the black-throated finch from going extinct? The finch is endangered because its habitat continues to be lost. So its recovery relies upon halting the ongoing loss of habitat – and ultimately, increasing it. Achieving this would require a political willingness to prioritise endangered species protection.
Australia has already lost hundreds of its unique plants and animals forever. In just the last few years, we have seen more mammals and reptiles disappear to extinction. If we continue on our current path, the southern black-throated finch could be among the next to go.
Stephen Garnett, Charles Darwin University; Alienor Chauvenet, Griffith University; April Reside, The University of Queensland; Brendan Wintle, University of Melbourne; David Lindenmayer, Australian National University; David M Watson, Charles Sturt University; Elisa Bayraktarov, The University of Queensland; Hayley Geyle, Charles Darwin University; Hugh Possingham, The University of Queensland; Ian Leiper, Charles Darwin University; James Watson, The University of Queensland; Jim Radford, La Trobe University; John Woinarski, Charles Darwin University; Les Christidis, Southern Cross University; Martine Maron, The University of Queensland; Molly K Grace, University of Oxford; Paul McDonald, University of New England, and Sarah Legge, Australian National University
Glossy Black-Cockatoos used to be common on South Australia’s Kangaroo Island until possums started eating their eggs and chicks. After volunteers helped protect nest hollows and erect safe nest boxes, the population more than doubled.
But how do you measure such success? How do you compare cockatoo nest protection with any other investment in conservation?
Unfortunately, we have few ways to compare and track the different efforts many people may be making to help conserve our natural treasures.
That’s why a group of us from a dozen Australian universities along with scientists and private researchers around the world have created metrics of progress for both our understanding of how to manage threats of different intensity, and how well that management has been implemented. We also provide guidance on what still needs doing before a threat no longer needs active management.
For the first time, we looked at every threatened bird in Australia to see how well – or not – they are managed. Hopefully, we can use this to avoid compounding our disastrous recent track record of extinctions in Australia.
The state of Australian birds
What we did differently was collect the same data across different species, which meant we could compare conservation efforts across all bids.
When we applied these metrics to Australia’s 238 threatened bird species, the results were both encouraging and daunting. The good news is that we understand how to reduce the impact of about 52% of the threats – although of course that means we know little about how to deal with the other 48%.
But the situation is decidedly worse when we consider how effectively we are putting that research into practice. Only 43% of threats are being managed in any way at all – and just a third of the worst threats – and we are achieving good outcomes for just 20%.
But at least we now know where we are. We can celebrate what we have accomplished, appreciate how much needs doing, and direct our efforts where they will have the greatest benefit.
The threats to our birds
Introduced mammals, particularly cats, have been (and continue to be) a significant threat to Australian birds. Although we have successfully eradicated feral animals on many islands, saving many species, they remain a grave threat on the mainland.
The effect of climate change is becoming the top priority threat for the future. About half of all threatened birds are likely to be affected by increases in drought, fire, heat or sea level. Given the policy prevarication at a global level, targeted research is essential if birds are to be helped to cope.
By looking at multiple species, we can also identify what helps successful conservation. Monitoring, for instance, has a big impact on threat alleviation – better monitored species receive more attention.
There is also – unsurprisingly – a strong connection between knowledge of how to manage a threat and successful application of that knowledge. Often policy people want instant action, but our work suggests that action before knowledge will squander money.
Where to from here?
So what can we use this analysis for? One use is helping species close to extinction.
Using the same approach for multiple species groups, it is apparent that, while birds and mammals are in a parlous state, the most threatened fish are far worse off. We can also identify some clear priorities for action.
Finally, we must acknowledge this work emerged not from a government research grant, but from a non-government organisation (NGO). BirdLife Australia needed an overview of the country’s performance with threatened birds and was able to draw on the volunteered skills of biologists and mathematicians from around the country, and then the world.
Indeed, one of the future projects will be using the new assessment tool to see just how much of the conservation action around the country is being driven by volunteers, from the many people who contributed their knowledge and skills to this paper through to those keeping glossy black-cockatoo chicks safe on Kangaroo Island.
Stephen Garnett, Professor of Conservation and Sustainable Livelihoods, Charles Darwin University; Alienor Chauvenet, Lecturer, Griffith University; April Reside, Researcher, Centre for Biodiversity and Conservation Science, The University of Queensland; Brendan Wintle, Professor Conservation Ecology, University of Melbourne; David Lindenmayer, Professor, The Fenner School of Environment and Society, Australian National University; David M Watson, Professor in Ecology, Charles Sturt University; Elisa Bayraktarov, Postdoctoral Research Fellow in Conservation Biology, The University of Queensland; Hayley Geyle, Research Assistant, Charles Darwin University; Hugh Possingham, Professor, The University of Queensland; Ian Leiper, Geospatial Scientist, Charles Darwin University; James Watson, Professor, The University of Queensland; Jim Radford, Principal Research Fellow, Research Centre for Future Landscapes, La Trobe University; John Woinarski, Professor (conservation biology), Charles Darwin University; Les Christidis, Professor, Southern Cross University; Martine Maron, ARC Future Fellow and Associate Professor of Environmental Management, The University of Queensland; Molly K Grace, Postdoctoral Fellow in Zoology, University of Oxford; Paul McDonald, Associate professor, University of New England, and Sarah Legge, Associate Professor, Australian National University
Plastic pollution has the potential to cause the worst damage to seabirds in the seas around Aotearoa New Zealand, where many of them come to feed and breed.
Aotearoa boasts the greatest diversity of seabirds in the world. Of the 360 global seabird species, 86 breed here and 37 are endemic, which means they breed nowhere else.
Some 90% of New Zealand’s seabirds are threatened with extinction. They (and many other marine species) are under pressure from pollution, climate change, and overexploitation of marine resources. Plastic pollution could be the final nail in the coffin for many seabirds that are already struggling for survival.
Plastic – not so fantastic
Every week, another grotesque story illustrates the impact of plastic in the environment. A whale was recently found with 80 plastic bags in its stomach – it died, of course.
One-third of marine turtles have died or become ill due to plastic ingestion in Aotearoa New Zealand.
A 2015 study suggested that 99% of seabirds would be ingesting plastic by 2050. The authors also predicted that seabirds in our backyard, the Tasman Sea (Te Tai o Rēhua) would be the hardest hit, because of the high densities of seabirds foraging in the region, and the overlap with plastic. This not that surprising, given that the earliest observations of Aotearoa’s seabirds ingesting plastic go back to 1958.
Sentinels of ocean plastic pollution
Seabirds are particularly vulnerable to ingesting plastics because most species feed at or near the ocean surface. They forage along eddies and oceanic convergence zones – the same areas where marine plastics accumulate. The impacts of plastic on seabirds and other marine wildlife include death by entanglement. Ingested plastic can inhibit a bird’s feeding capacity, leading to starvation or internal ulcers, and eventually death.
Flesh-footed shearwater populations in Aotearoa may have declined up to 50% to around 12,000 pairs since the 1980s, and have gone extinct at some of their Hauraki Gulf breeding sites. These declines continue in spite of predator eradication and an end to harvesting on many of the islands where they breed.
Autopsies of birds caught in fisheries in Aotearoa’s waters show flesh-footed and sooty shearwaters are more likely to contain plastic fragments than other species. Plastic fragments found in New Zealand flesh-footed shearwater colonies showed a linear relationship between the number of nest burrows and plastic fragments, indicating that plastic ingestion may be a driver in their population decline.
Toxic plastic soup
In Australia, up to 100% of flesh-footed shearwater fledglings contained plastic, the highest reported for any marine vertebrate. Fledglings with high levels of ingested plastic exhibited reduced body condition and increased contaminant loads.
The chemical structure of plastics means that they act as toxin sponges, attracting harmful contaminants from the surrounding seawater, including persistent organic pollutants and heavy metals. When an animal ingests plastic, there is the potential for those toxic chemicals to leach into its tissues.
Chemicals such as PCBs and flame retardants that are added to plastics during manufacture have been found in seabird tissue around the Pacific. High concentrations of toxic chemicals can retard growth, reduce reproductive fitness and, ultimately, kill.
Sooty shearwater (tītī) chicks, which are harvested and consumed by Māori in Aotearoa, have a high potential for ingesting plastic, given evidence of plastic ingestion in shearwaters from Australia and anecdotal evidence from harvesters on Stewart Island (Rakiura). The closely related short-tailed shearwater, which breeds in Australia, has also been show to consume plastic. In one study, 96% of chicks contained plastics in their stomachs and chemical loads in their tissue.
Ocean health and human health
Few, if any, studies have specifically looked at contaminant loads derived from plastics in any species of seabird in Aotearoa. However, Elizabeth Bell from Wildlife Management International is now collecting samples of preen glands, fat and liver tissue for analysis of toxic chemicals in bycatch birds found with plastic inside them. This research is crucial to understanding the implications of the transfer of toxins to people from harvested species that ingest plastic.
Seabirds are the sentinels of ocean health. They tell us what we can’t always see about the health of the oceans and its resources that we rely on.
Plastics are sold to us on the perceived benefits of strength, durability and inexpensive production. These qualities are now choking our oceans.
In a few decades, we have produced an estimated 8.3 billion tonnes. The expedited pace of production has not been met with adequate waste management and recycling capacity to deal with it all. As a result, an estimated 8 million tonnes of plastic pollute the environment each year.
Global production of plastics is doubling every 11 years. It is predicted to be an order of magnitude greater than current production levels by 2040. The time is ripe for the initiation of an international agreement to lessen plastic pollution in the world’s oceans and save our seabirds and marine wildlife.