Cockatoos and rainbow lorikeets battle for nest space as the best old trees disappear


Shutterstock

Gregory Moore, The University of MelbourneThe housing market in most parts of Australia is notoriously competitive. You might be surprised to learn we humans are not the only ones facing such difficulties.

With spring rapidly approaching, and perhaps a little earlier due to climate change, many birds are currently on the hunt for the best nesting sites.

This can be hard enough for birds that construct nests from leaves and twigs in the canopies of shrubs and trees, but imagine how hard it must be for species that nest in tree hollows.

They are looking for hollows of just the right size, in just the right place. Competition for these prime locations is cut-throat.

Sulphur-crested cockatoos battling for spots

Sulphur-crested cockatoos, Cacatua galerita, are relatively large birds, so naturally the hollows they nest in need to be quite large.

Unfortunately, large hollows are only found in old trees.

It can take 150 years or more before the hollows in the eucalypts that many native parrot species nest in are large enough to accommodate nesting sulphur-crested cockatoos. Such old trees are becoming rarer as old trees on farms die and old trees in cities are cleared for urban growth.

In late winter, early spring you quite often find sulphur crested-cockatoos squabbling among themselves over hollows in trees.

A cockatoo sits in a hollow.
It can take 150 years or more before the hollows in the eucalypts that many native parrot species nest in are large enough to accommodate nesting sulphur-crested cockatoos.
Shutterstock

These squabbles can be very loud and raucous. They can last from a few minutes to over an hour, if the site is good one. Once a pair of birds takes possession and begins nesting, they defend their spot and things tend to quieten down.

The stakes are high, because sulphur-crested cockatoos cannot breed if they don’t have a nesting hollow.




Read more:
Don’t disturb the cockatoos on your lawn, they’re probably doing all your weeding for free


Enter the rainbow lorikeets

In parts of southeastern Australia, rainbow lorikeets, Trichoglossus moluccanus (and/or Trichoglossus haematodus), have expanded their range over the past couple of decades. It is not uncommon to see sulphur-crested cockatoos in dispute with them over a hollow.

The din can be deafening and if you watch you will see both comedy and drama unfold. The sulphur-crested cockatoos usually win and drive the lorikeets away, but all is not lost for the lorikeets.

Sometimes the hollows prove unsuitable — usually if they are too small for the cockatoos — and a few days later the lorikeets have taken up residence. Larger hollows are rarer and so more highly prized.

A rainbow lorikeet shelters in the hollow of a tree.
It is not uncommon to see sulphur-crested cockatoos in dispute with rainbow lorikeets over a hollow.
Shutterstock

How hollows form

Many hollows begin at the stubs of branches that have been shed either as part of the tree’s growth cycle or after storm damage. The wood at the centre of the branch often lacks protective defences and so begins to decay while the healthy tree continues to grow over and around the hollow.

Other hollows develop after damage to the trunk or on a large branch, following lightning damage or insect attack. Parrots will often peck at the hollow to expand it or stop it growing over completely. Just a bit of regular home maintenance.

Sulphur-crested cockatoos can often be seen pecking at the top of large branches on old trees, where the branch meets the trunk. They can do considerable damage. When this area begins to decay, it can provide an ideal hollow for future nesting.

Sadly, for the cockatoo, it may take another century or so and the tree might shed the limb in the interim. Cockatoos apparently play a long game and take a very long term perspective on future nesting sites.

A cockatoo sits in a hollow.
Every effort must be made to ensure old, hollow-forming trees are preserved.
Shutterstock

Which trees are best for hollows?

In watching the local battles for parrot nesting sites, some tree species are the scenes of many a conflict.

Sugar gums, Eucalyptus cladocalyx, were widely planted as wind breaks in southern Australia and they were often lopped to encourage a bushier habit that provided greater shade.

Poor pruning often leads to hollows and cavities, which are now proving ideal for nesting — but it also resulted in poor tree structure. Sugar gums are being removed and nesting sites lost in many country towns and peri-urban areas (usually the areas around the edges of suburbs with some remaining natural vegetation, or the areas around waterways).

A rainbow lorikeet hides in a hollow.
Many species need hollows for nests.
Shutterstock

Old river red gums, (Eucalyptus camaldulensis) growing along our creeks and rivers are also great nesting sites. They are so big they provide ideal sites for even the largest of birds.

These, too, are ageing and in many places are declining as riverine ecosystems suffer in general. Even the old elms, Ulmus, and London plane trees, Platanus x acerifolia — which were once lopped back to major branch stubs each year, leading hollows to develop — are disappearing as they age and old blocks are cleared for townhouses.




Read more:
The river red gum is an icon of the driest continent


Protecting tree hollows

Cavities in trees are not that common. Large cavities are especially valuable assets. They are essential to maintaining biodiversity because it is not just birds, but mammals, reptiles, insects and arachnids that rely on them for nesting and refuge.

If you have a tree with a hollow, look after it. And while some trees with hollows might be hazardous, most are not. Every effort must be made to ensure old, hollow-forming trees are preserved. Just as importantly, we must allow hollow-forming trees to persist for long enough to from hollows.

We consider our homes to be our castles. Other species value their homes just as highly, so let’s make sure there are plenty of tree hollows in future.The Conversation

Gregory Moore, Doctor of Botany, The University of Melbourne

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

DIY habitat: my photos show chainsaw-carved tree hollows make perfect new homes for this mysterious marsupial


William Terry, Author provided

William Terry, Southern Cross UniversityEnvironmental scientists see flora, fauna and phenomena the rest of us rarely do. In this series, we’ve invited them to share their unique photos from the field.


As a result of logging and severe bushfires, Australian wildlife is facing a severe shortage of tree hollows — holes in the trunks and branches of large old trees. More than 300 species of birds and mammals, including possums, bats, cockatoos, owls and kookaburras, rely on tree hollows for shelter or breeding.

A sacred kingfisher using a natural tree hollow for nesting.
William Terry

In Australia, hollows are usually formed through the decay of a tree scar, and it can take hundreds of years for tree hollows big enough for medium-sized animals to form naturally.

This includes phascogales — the rat-sized, carnivorous marsupials that live in open woodlands across Australia and are the focus of my research and photography. But like many of Australia’s forest-dwelling mammals, phascogales are vulnerable to extinction.

So with hollows becoming harder to find, I venture into forests and study how well artificial hollows, made with chainsaws, can replace them. And, incredibly, it’s working: my research shows phascogales and other native animals are enthusiastically moving into the new real estate.

Meet the mysterious brush-tailed phascogale

Phascogales are an important species to Australia but, unfortunately, their cryptic behaviour and nocturnal habits mean people rarely see them.

Brush-tailed phascogales live in trees, but will come to the ground to forage for food among leaf litter and fallen timber.
William Terry
Phascogales belong to the same family as the Tasmanian devil, quoll (pictured) and the tiny antechinus.
William Terry, Author provided

Phascogales feed on insects after stripping bark from eucalypts. But through my close interactions and radio tracking, I’ve documented phascogales eating other more unusual foods, including bird eggs and sometimes even small birds, such as grey-shrike thrush.

I’ve also recorded them taking dead birds, such as the rosella pictured below. They even have a reputation among farmers as being a fierce chicken killer, but this may be exaggerated.

A phascogale inspects a dead crimson rosella it found at the base of a tree. Moments later, this phascogale dragged the bird away. It was unclear what happened next.
William Terry

Phascogales have an unusual life. Shortly after mating between April and May, all males die at about 11 months of age from stomach ulcers. This frees up resources for the next generation of young joeys that will emerge from the nest in early summer.

But will they survive in the future?

Tragically, at least one species, the brush-tailed phascogale, is threatened with extinction, primarily due to habitat loss, climate change, and feral predators such as foxes and cats.

The brush-tailed phascogale (Phascogale tapoatafa tapoatafa) occurs across the eastern side of Australia, from southern Queensland to Victoria. It’s now extinct in South Australia.

Likewise, the much smaller red-tailed phascogale (Phascogale calura) once survived across a vast swathe of land from Western Australia to Victoria. Today, it survives only in small pockets in the Western Australia wheatbelt.

Brush-tailed phascogales were once known as ‘bottle-brush squirrels’, due to the stunning resemblance of its tail to the iconic native flowers.
William Terry
The red-tailed phascogale has been lost from much of its former range and now only exists in the Western Australian wheatbelt.
William Terry, Author provided

Household cats are a particularly major issue for phascogales, and many cat owners in central Victoria have a story about their cat bringing home a phascogale (so please keep your pet cat inside at all times).




Read more:
Don’t let them out: 15 ways to keep your indoor cat happy


Last year, research confirmed climate change would reduce the available areas phascogales could survive. This research found areas with a phascogale-friendly climate would decline by up to 79% in Queensland, 67% in Victoria and 17% in NSW, by 2070.

Climate change also threatens to bring longer, more frequent and severe heatwaves. For phascogales and many other mammals, this could be a death sentence.

Tree hollows with thick walls can protect the animals sheltering inside from the high temperatures outside.

But these are getting increasingly rarer, and this is where my research on chainsaw hollows comes in. Thick-walled hollows may be very important for the long-term survival of phascogales and other species in a warming climate.

A relative to the phascogale, the tiny agile antechinus commonly uses tree hollows on the ground.
William Terry, Author provided

Carving them a home

A chainsaw hollow is a cavity constructed inside a tree. A faceplate is then attached over the top, with a hole drilled into it for the animal to enter. They offer refuge for Australia’s endangered mammals and birds.

For our project, we carved 45 chainsaw hollows in dry forests and woodland where phascogales are known to occur. We also installed similar-sized nest boxes — which are more commonly used to offset the loss of hollows — on nearby trees. We monitored these for two and a half years.

A chainsaw hollow constructed for phascogales.
William Terry, Author provided
Chainsaw hollow creation is a specialised skill. Here, tree climber Lachlan installs a chainsaw hollow on a red ironbark tree.
William Terry, Author provided

Research from 2018 shows nest boxes offer little protection from outside temperatures. I’ve collected data, which is not yet published, that confirms this.

My research shows chainsaw hollows provide 27% more protection from extreme temperatures during heatwaves compared to nest boxes, which provided almost no protection.




Read more:
The world endured 2 extra heatwave days per decade since 1950 – but the worst is yet to come


Two phascogales peeking out of a nest box.
William Terry, Author provided

So it’s no wonder we observed and recorded phascogales and the more common sugar glider (Petaurus notatus) more frequently sheltering in chainsaw hollows than in nearby nest boxes.

Other animals used the chainsaw hollows, too. This includes the feather-tailed glider, yellow-footed antechinus, and the white-throated treecreeper.

Brush-tailed phascogale inspects a chainsaw hollow.
Sugar gliders also frequently used chainsaw hollows.
William Terry

But like nest boxes, the chainsaw hollows showed signs they would be only an interim measure, requiring maintenance with bark growing over entrance holes and issues with a buildup of moisture.

In any case, further research into this species is needed, as it will aid land managers to conserve this enigmatic species as more challenges are thrown their way into the future.




Read more:
Photos from the field: the stunning crystals revealing deep secrets about Australian volcanoes


The Conversation


William Terry, PhD Researcher, Supervision by Associate Prof. Ross Goldingay, Southern Cross University

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