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The unassuming dusky hopping mouse. Ben Moore

You should stop skylarking about with those bloody desert mice and try and stop those woody weeds. I could see clear through that paddock in the ‘60s. Now look at it. That scrub costs us tens of thousands of dollars in lost fodder and it’s almost impossible to muster the livestock.

That blunt assessment of our research, first offered by a local farmer in Australia’s arid rangelands almost seven years ago, raised an irresistible question for us as field ecologists. Why are Australia’s (and many others around the world) grasslands becoming woodier?

It certainly was a question worth asking. Shrub encroachment – an increase in the cover of woody shrubs in areas once dominated by grasses – is not just an issue in Australia.

In two recent papers published in the journals Ecography and the Journal of Animal Ecology, we looked at one key reason why trees are invading grasslands, and how we could stop them. And it all comes down to tiny desert mice.

Shrub invasion

“Invasive native vegetation”, as bureaucrats call it, is a major problem for livestock producers in drylands throughout the world. This is because the shrubs compete for space and light with the grasses needed to feed their cattle and sheep.

Shrub encroachment ‘inside’ the Dingo Fence. Dr Ben Moore

It is a hard problem to tackle. Clearing and fire are the most common methods of controlling woody shrubs. But these methods are laborious and often hard to implement on large scales.

Removing shrubs is also contentious because these are typically native species that provide important habitat for wildlife. The New South Wales parliament’s controversial relaxation in November of regulations governing vegetation clearing were designed partly to allow farmers to remove invasive native vegetation.

What’s going on?

The causes for the spread are complex and poorly understood. Shrub encroachment is often attributed to overgrazing by livestock, which favours the growth of shrubs over grasses. It has also been linked to a reduction in bushfires that wipe out the shrubs and an increase in atmospheric carbon dioxide, which can promote their growth.

However, we suspected another important factor could be at play. And it was those little desert mice that provided us with a big clue – and a possible solution.

Since European settlement, livestock grazing and the introduction of foxes, feral cats and rabbits have decimated Australia’s native mammals, especially in arid and semi-arid areas.

The bilbies, bettongs, native rodents and other small mammals that became rare or extinct across much of the continent in the early 20th century once played essential roles in Australian ecosystems, by shifting vast amounts of soil and consuming vegetation and seeds.

Historical accounts suggest that shrub encroachment quickly followed European settlement and mammal extinctions in many areas. This coincidence led us to ask: could the loss of native mammals be making Australia’s drylands woodier?

Hopping to it

To answer this question, we went to the northwest corner of NSW. Here the Dingo Fence marks the border with Queensland and South Australia.

The Dingo Fence. Ben Moore

We wanted to know whether the local extinction of a native mammal, the dusky hopping mouse, which eats shrub seeds and seedlings, would allow more shrubs to grow. The Dingo Fence was the perfect study site because dusky hopping mice are common on the northwest side, “outside” the fence, where dingoes are present.

Dingoes keep fox numbers down, which are the mouse’s major predator. However, dusky hopping mice are rare on the “inside” of the fence (the NSW side), where dingoes are less common and foxes roam.

We first used historical aerial photographs to show that shrub cover was consistently higher inside the dingo fence (rodents rare) than outside (rodents common). We then did field surveys, which showed that the numbers of shrubs, their seedlings and their seeds were greater where rodents were rare.

We also showed that dusky hopping mice were major consumers of shrub seeds and capable of keeping the numbers of shrub seeds in the soil down.

Fieldwork in the Strzelecki Desert. Dr Ben Moore Going wild again

These results are exciting because they suggest that the loss of native mammals such as the dusky hopping mouse may be an important and overlooked driver of shrub encroachment, not only in arid Australia but also globally.

Perhaps more exciting, however, is how we can apply our work. Our research suggests that “rewilding” drylands by re-establishing rodents and other native mammal species that eat shrub seeds and seedlings, such as bettongs and bilbies, could curb the shrub invasion.

Although an abstract and even controversial idea, rewilding of native mammals would provide a long-term solution to a problem that has affected pastoralists for more than a century.

Further, it would represent a natural and cost-effective strategy with enormous benefits for the conservation of imperilled native mammals.

Before we can do so, we have to control foxes and feral cats across vast areas, which is no small feat. However, the economic and conservation potential make it an approach that is well worth taking seriously.

Mike Letnic has received funding from the Hermon Slade Foundation and Australian Research Council.

Christopher Edward Gordon does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

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Sulphur-crested cockatoos form long-term pair bonds, perhaps explaining their emotional intelligence. Ian Sanderson/Flickr, CC BY-NC

July on the Northern Tableland, near Armidale in New South Wales, is usually the beginning of the breeding season and field observations start early.

I sat and watched in freezing temperatures. The sun was just rising above the horizon of this 1000m-high plateau when through binoculars I saw a young lone magpie, walking gingerly, literally tip-toeing, occasionally interrupted by little bouts of running and, unusually, heading straight for its territorial boundary.

In the last stretch to the border, the bird edged along a row of pine trees, staying low, and kept looking over its shoulder, especially when crossing the neighbour’s border. Shortly afterwards, a female was seen in his company.

Later, the male backtracked and, when far enough into his own territory, started foraging rather aimlessly as if nothing had happened.

The magpie who snuck over the border. Gisela Kaplan

What had I witnessed? Did this young male magpie understand that he was breaking several important magpie social rules and could face punishment for this transgression if caught? Did he have a sense of morality?

Science has traditionally shunned the idea of emotions in animals, not just for fear of anthropomorphism or over-interpretation, but also because there is a very long cultural history that played out a divide between mind and body and reason and emotions.

Reason, thinking and making judgements were stubbornly thought to be outside the capacity of animals. For a long time it was not believed that animals were even capable of feeling pain, let alone complex emotions. We now know that is far from the truth.

Birds with feelings

Pet owners have always known that their pets can be affectionate, sulky, jealous, sad, excited and deliberately naughty, as well as doing extraordinary things for their owners. The animals we know best in this regard are obviously dogs and cats.

Charles Darwin was the first to discuss emotions in animals in the mid-19th century. A century later, Niko Tinbergen addressed the vexing question of emotions.

Following on from Darwin, he identified “four Fs” as part of survival: fight, flee, fornicate and feed. These translate into basic feelings of fear, hunger and sexual drive – now called motivational states.

Tawny frogmouths are monogamous. cskk/Flickr, CC BY-NC-ND

But there is a lot more to bird emotions. Dangerous and horrible experiences are usually remembered. Memory helps survival. Modern urban birds have been shown to remember faces of people considered dangerous and threatening.

We now know that the bird brain is lateralised (each side of the brain controls a different set of functions) as in humans and other vertebrates. The right hemisphere expresses intense emotions (such as fear and attack). The left hemisphere has routine, considered responses and may inhibit some of the strong responses of the right hemisphere.

So birds are more similar to humans than had ever been thought, but with an important difference: birds are generally not aggressive without cause. Technically, aggression is an emotion that is dysfunctional, has no purpose and often even harms the individual displaying it.

Birds can certainly get very angry – and the owner of a galah or corella would be well advised not to get near this bird when the head feathers are raised — but birds can be joyful and playful, can get depressed and, as studies have shown, a neglectful or bare environment can even make them pessimistic.

Birds may feel for others (have empathy) and even console them, may have a sense of justice, may show deep affection for their partner and grieve for their loss. I witnessed the mate of a fatally injured tawny frogmouth not moving from the spot next to its dead partner for three days, and then dying on the fourth.

Social smarts

Australian native birds have an unusually high percentage of pair-bonding (over 90% of species) and the highest concentrations of cooperative species (relatives or siblings helping at the nest) anywhere in the world. Cockatoos bonding for life often have intense close partnerships, which are nurtured by constant grooming and attention to each other’s needs.

Such intense cohabitation of individuals, often for many years (how about 60 years of “marriage” in sulphur-crested cockatoos?), may also create frictions and dissatisfactions that require solutions to keep the pair or group together.

For instance, the lazy helper at the nest who only pretends to help in feeding, as happens among white-winged choughs, may get scolded by an adult. A group of apostlebirds building a mud nest together, transporting mud to the nest in relays, may spot an individual that is not pulling its weight.

I have witnessed on several occasions near Copeton Dam (in Inverell, NSW) apostlebirds become so outraged that they approach the individual with heightened calling and may even peck it until the intimidated individual falls back into line and does its share.

Empathy, altruism and consoling the injured or vanquished have all been observed in birds, thought to be the ultimate in consideration for another individual’s state of mind.

For instance, there are observations of dusky wood-swallows (belonging to the same family of birds as butcherbirds and magpies) in Western Australia’s Wheatbelt hassling a restless flycatcher with a larva in his beak, perched on a branch. One wood-swallow flew above the flycatcher, while the other simultaneously flew directly at it, snatched the larva from its beak while it was distracted by the other bird hovering overhead, and took it away. So who got the prize?

If all behaviour in animals is selfish, then the one who caught it should have gulped it down, but it did not. It gave it to the bird that had distracted the flycatcher. Perhaps the two birds reversed roles in the next, similar, situation. But it still meant overcoming the temptation to eat.

A noisy miner, one of the cooperative honeyeaters, I had hand-raised grew up over several weeks in the company of very young ridgeback pups near the edge of a nature reserve in a NSW coastal area.

One pup was sleeping on the porch in the sun and I was some distance away. I was alerted by the alarm calls of the noisy miner and turned around to see it swooping right down to a lace monitor’s head – doing so over and over again. I ran as quickly as I could, by now also shouting once the risk to the pup was more than apparent.

When the monitor spotted me, it turned and fled. The noisy minor had risked its life to save the pup. At no other occasion did the bird attempt to swoop a lace monitor. Its response was very specific to this situation.

And, as I have been asked often, could birds have a sense of humour? Perhaps.

Our galah, Philip, deeply affectionate (and jealous!) had learned the names of all our dogs and was such a good mimic of our voices that he could easily and effectively call the dogs to attention.

Imagine the picture: a bird less than a foot tall, standing on the floor and calling four massive Rhodesian ridgebacks to attention. Then, when he got them all in line in front of him, he walked away, swaying his head and even making little chuckling sounds.

The degree to which emotions and complex feelings for others were developed may well depend on social organisation. It may be that birds with long-term social bonds show more complex behaviour and brains than those whose associations are only fleeting.

What they get out of it is perhaps not debatable — more joy, more grief, but also a greater degree of safety and usually a longer life. There are clear benefits of sticking together in a difficult and fickle continent.

Gisela is speaking at the Mornington Peninsula Regional Gallery on Tuesday, December 6, and Wednesday, December 7.

Professor Gisela Kaplan received funding from the ARC and bequests from private benefactors She is at the School of Science and Technology at the University of New England, Armidale, NSW and there are no conflicts of interests or personal benefits derived from writing this article.