Hidden in plain sight: introducing the new subspecies of red-tailed black-cockatoo!
Scientists from AMRI, University of Sydney, University of Edinburgh and CSIRO conducted the first comprehensive genetic assessment of the red-tailed black-cockatoo across its entire distribution. The result is a new subspecies; it only took extensive Museum collections, carefully gathered over decades, and an extensive genetic analysis to find them!
The red-tailed black-cockatoo (Calyptorhynchus banksii) is one of Australia’s most iconic bird species. This large parrot can be recognised by the spectacular red (adult male) or orange-yellow (adult female) panels in its tail. Adult females also have orange-yellow bars across their chests and tails, and spots on their heads and wings. These birds are truly magnificent!
Red-tailed black-cockatoos (Calyptorhynchus banksii) displaying the distinct orange-yellow tail panels of a female (left) and the red tail panels of a male (right).
Image: Patrick Tomkins© Patrick Tomkins
Red-tailed black-cockatoos are found in pockets of eucalypt woodland throughout Australia, from temperate forests to tropical savannahs and desert rangelands. Like most cockatoos, they too have a raucous call that can be heard from a distance. It has been described as sounding like a ‘rusty windmill’. And the evolution of the red-tailed black-cockatoo is as beautiful as the birds themselves, at least from a biologist’s perspective!
In the past, the species was divided into five groups (‘subspecies’), known as banksii, graptogyne, macrorhynchus, naso, and samueli. These subspecies show physical differences in their plumage, body size, bill shape, and bill size, reflecting their different habitats and diets. For example, northern birds are bigger than southern birds, and subspecies that eat large fruits and seeds have larger bills. But there has been debate about whether the five subspecies actually reflect the evolutionary history of the species.
Prior to this study five subspecies of red-tailed black-cockatoos (Calyptorhynchus banksii) were described based on differences in plumage, body size and bill shape/size. This Figure is adapted from Figure 1 in the associated paper (i.e. Ewart et al., 2020), using Adobe Illustrator.
Image: Kyle Ewart© Kyle Ewart
Unfortunately, the red-tailed black-cockatoo is suffering from habitat destruction. Like other cockatoo species, red-tailed black-cockatoos cannot excavate their own tree hollows, yet they rely on them for nesting. The red-tailed black-cockatoo is also targeted in the illegal pet trade. The two southern subspecies are threatened, with only approximately 1,000 graptogyne 15,000 naso individuals remaining in the wild. Genetic information is sorely needed to inform the management strategies for this species.
We conducted a genetic assessment of the red-tailed black-cockatoo across its entire range. Collecting the samples for such a study would normally have taken an immense amount of time and resources. Fortunately, specimens have been collected over many decades and are stored in museums throughout Australia. We were able to extract a large amount of genetic data from these specimens, some of which were >100 years old, allowing us to investigate the relationships between the current subspecies.
We estimated that the ancestor of the species appeared within the past ~1.28 million years. Our data set allowed us to identify five ‘conservation units’ within the species, which will help guide effective conservation strategies. Protecting and maintaining these distinct units of genetic variation will maximize the chances of the species persisting in the wild. We also identified that the graptogyne subspecies of western Victoria and south-eastern South Australia has the lowest level of genetic diversity, and is likely to suffer from inbreeding. The genetic data from our study allow us to outline a strategy to rescue graptogyne from its continued loss of genetic diversity.
Intriguingly, the five conservation units that we identified were not the same as the subspecies that had been previously defined. This led us to make two changes to the formal classification (taxonomy) within the species. First, we did not find any genetic separation between the two subspecies from northern Australia, banksii and macrorhynchus. The sparsely wooded plains fringing the Gulf of Carpentaria were supposedly the boundary between these two subspecies, and they are known to separate many species across this region. Instead, we concluded that the two northern subspecies should be combined into a single subspecies, with the name banksii.
A red-tailed black-cockatoo (Calyptorhynchus banksii macrorhynchus) coming down for a drink near Derby, northern Western Australia.
Image: Patrick Tomkins© Patrick Tomkins
Our second change was to assign the Western Australian populations of samueli to a new subspecies. We found that these populations were most closely related to naso, rather than to the other populations of samueli found elsewhere in Australia. We call the new subspecies escondidus, meaning ‘hidden’ in Spanish/Portuguese, because for a long time it was ‘hidden in plain sight’ as part of samueli. It only took decades of Museum collections and an extensive genetic analysis to recognise them! The apparent physical similarities between escondidus and samueli are likely to be the result of a process known as convergent evolution. They have evolved to be similar because they both feed on the ground and live in similar arid and semi-arid habitats. Despite this similarity, an avian morphologist (Richard Schodde; a co-author of this study) contributed his analysis which found specific features that can be used to distinguish escondidus from samueli.
As with recognising a new species, a new subspecies requires a “holotype” (i.e., the specimen from which the subspecies or species was first described). Here the holotype is a specimen held at CSIRO’s Australian National Wildlife Collection (ANWC), and it is specimen ANWC B37847 that gets the honour.
Image: Gordon Gullock© Gordon Gullock
This extensive genetic assessment of the red-tailed black-cockatoo has shed light on the species’ evolution, taxonomy and conservation. We hope that this study can be used to inform conservation strategies to ensure the ongoing survival of this magnificent species.
Kyle Ewart, PhD Candidate and Research Associate, Australian Centre for Wildlife Genomics, Australian Museum Research Institute; and the University of Sydney.
Further information:
Ewart, K.M., Lo, N., Ogden, R. et al. Phylogeography of the iconic Australian red-tailed black-cockatoo (Calyptorhynchus banksii) and implications for its conservation. Heredity (2020). https://doi.org/10.1038/s41437-020-0315-y.
Acknowledgements:
This was a large collaborative study, involving scientists from AMRI (Rebecca Johnson, Greta Frankham and Mark Eldridge), University of Sydney (Nathan Lo and Simon Ho), University of Edinburgh (Rob Ogden) and CSIRO (Leo Joseph and Richard Schodde). This study would not have been possible without samples from the Australian Museum, Australian National Wildlife Collection, Western Australian Museum and Museum Victoria. We are very appreciative of the staff at these Museums that assisted us, and to those that have added to these collections throughout the decades.
