Protected land, including national parks, are a cornerstone of conservation. Once an area is legally protected, it is tempting to assume that it is shielded from further degradation.
However, our research, published in the journal Global Ecology and Conservation, has found Australia’s national parks are under serious threat of overgrazing. Significantly, native kangaroos are major contributors to the problem.
In some places we looked at, the effect of overgrazing in protected areas was just as pronounced as on private land with no legal protection at all.
In the public debate over culling and otherwise managing kangaroo populations, attention is typically divided between their economic impact on people versus welfare concerns. But there’s a third unwilling participant in this dilemma: the thousands of other native species affected when native grazer populations grow out of control.
Protected from what?
National parks and other protected areas can be safeguarded in a variety of legal ways. Activities such as grazing of domestic stock, building, cropping and some recreational activities (hunting, fishing, dogs) are usually restricted in protected areas. However, previous research has found protected areas continue to face intense pressure from agriculture, urbanisation, mining, road construction, and climate change.
Less conspicuously, the loss of predators from many Australian ecosystems has let herbivore populations grow wildly. Overgrazing, or grazing that leads to changes in habitat, is now a key threat to biodiversity.
Overgrazing by herbivores affects native species such as the diamond firetail, which is declining in southeastern Australia due to loss of habitat and the replacement of native grasses with exotic species after overgrazing and fire. Overgrazing has also been shown to reduce the abundance and diversity of ground-dwelling reptiles.
In the face of a global extinction crisis, we need good evidence that national parks and reserves are serving their purpose.
To determine whether protected areas are being overgrazed, we assessed grazing impact on native vegetation at 1,192 sites across the entire agricultural region of South Australia. We looked at more than 600 plant species in woodlands, forests, shrublands, and grasslands.
The data were collected by monitoring programs, some of which included citizen scientists, aimed at tracking change in the condition of native vegetation.
We found that grazing pressure was already high on unprotected land when we began monitoring around 2005, and grazing impact has grown since then. On protected land, three things are happening as a consequence of inadequate management of grazing by native and introduced animals:
grazing impact in protected areas has substantially increased,
protected areas in some regions now show equally severe effects from grazing as seen on private land without any conservation protections, and
the character of our landscapes, including national parks, is set to change as the next generation of edible seedlings is lost from protected and unprotected ecosystems.
The increased severity of grazing in protected areas paints a dire picture. This threat adds to the rising pressure on protected areas for recreational access (and other uses).
The grass is not greener
It’s well accepted that introduced species such as deer, goats, horses, camels and rabbits badly affect Australia’s native vegetation. There are a variety of control measures to keep their populations in check, including culls and strong incentives for control on farmland. Control of feral animals is normally less contentious than control of endemic species like kangaroos, because we feel a custodial responsibility for native species.
But the numbers of native kangaroos and wallabies has also increased dramatically since 2011 as populations across Australia responded to an increase in feed at the end of the Millennium drought and reduced culling in settled areas due to changes in regulation and growing opposition to culls on animal welfare grounds.
Managing kangaroo populations, on the other hand, is a polarising issue. Arguments about culling kangaroos can be bitter and personal, and create perceptions of an urban-rural divide.
However, a few species – even if they are native – should not be allowed to compromise the existence of other native plants and animals, especially not where we have dedicated the land to holistic protection of biodiversity.
Extinction rates in Australia are extremely high, especially among plants. Research has also found conservation funding is disproportionately aimed at individual species rather than crucial ecosystems. We must address our reluctance to manage threats to biodiversity at the scale on which they operate.
Protected areas must be managed to meet clear biodiversity targets and control overgrazing, including from native species.
Welfare concerns for conspicuous native species need to be weighed against the concern for the many other less obvious native plant and animal species. If our national parks and reserves are not managed properly, they will fail to meet the conservation need for which they were established.
Patrick O’Connor, Associate Professor, University of Adelaide; Stuart Collard, Research Fellow, The Centre for Global Food and Resources, University of Adelaide, and Thomas Prowse, Postdoctoral research fellow, School of Mathematical Sciences, University of Adelaide
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Which is smarter: blue whales or orcas? – Prasaad, age 6.
There’s no simple answer. We don’t know for sure which one is smarter, because not everyone agrees on what “intelligence” means.
It’s true that blue whales and orcas (also called killer whales) are both smart. They both have very large brains. Orcas have particularly large brains compared to their overall body size.
But it’s not just about brain size. When it comes to measuring intelligence, we might also consider things like:
- the number of nerve cells in the brain;
- ability to navigate the deep, wide oceans;
- solving difficult problems;
- working in teams.
Let’s look at which animal is good at which skill.
What can a blue whale do?
There’s no doubt a blue whale is a very intelligent animal.
Blue whales eat krill, which are very tiny prawn-shaped animals that gather in huge swarms that are often far away from where blue whales give birth to their children. Despite the distance, blue whales are masters of finding krill. They are very good at navigating along coasts and across the deep, wide oceans.
In fact, blue whales are so smart they can work out if a swarm of krill is worth chasing. Blue whales are very good at finding krill that are fat and in big swarms so they do not waste their energy catching smaller swarms. Blue whales catch krill by rolling on their side and opening their mouths. It is a lot of work and they have to use a lot of energy to do it.
Blue whales also have excellent systems for communicating with each other.
What can an orca do?
Orcas are a kind of large dolphin and they have different strengths.
They are very good at working together. They form groups and hunt together for fish or other sea mammals – including whales. This is why they are called “killer whales”.
They are also expert communicators and have their own language – even certain noises that are used by a particular group of orcas to show they are in the group.
They both are very intelligent in their own way
Some scientists have wondered if you could measure intelligence by looking at how well animals teach their children how to behave – for example, how to find food, fight or stay safe.
Orcas are masters at teaching their children exactly what to do. This involves things like hunting in groups or sneaking up on a seal and grabbing it before sliding back into the water.
However, blue whales are also good at teaching their offspring skills such as long-distance navigation – in other words, finding their way around the vast oceans.
Both blue whales and killer whales have their own special behaviours and skills. We really can’t say which one is more intelligent because both are very intelligent in their own way.
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Australia’s water rats, or Rakali, are one of Australia’s beautiful but lesser-known native rodents. And these intelligent, semi-aquatic rats have revealed another talent: they are one of the only Australian mammals to safely eat toxic cane toads.
Our research, published today in Australian Mammalogy, found water rats in Western Australia adapted to hunt the highly poisonous toads less than two years after the toads moved into the rats’ territory.
The rats, which can grow to over 1kg, are the only mammal found to specifically target large toads, neatly dissecting the toads to eat their hearts and livers while avoiding the poisonous skin and glands.
Water rats are nocturnal and specially adapted to live in waterways, with webbed feet and soft water-resistant fur. Their fur is so impressive there was once a thriving water rat fur industry in Australia.
They can be found in lakes, rivers and estuaries, often living alongside people, in New South Wales, Queensland, Tasmania, South Australia, far north and southwest Western Australia, the Northern Territory, and Victoria, where they can even be seen along St Kilda Pier.
Water rats are also highly intelligent, as shown by their rapid adaptation to hunting and eating one of Australia’s most toxic introduced species – the invasive cane toad.
Cane toads were introduced to Australia in 1935 in an ill-fated attempt to control the cane beetle. They have spread across the north of the country at up to 60km per year, leaving devastation in their wake. Many native species, such as northern quolls, yellow-spotted monitors, and crocodiles, have suffered widespread declines, and in some cases local extinctions, as a result of eating cane toads.
The toads secrete a toxin in their parotoid glands (on the back, neck and shoulders) that can be fatal even in very small doses.
Eat your heart out
Cane toads arrived at our field site in the Kimberley, Western Australia, in 2011-12, leading to a crash in the populations of predators including numerous lizards and northern quolls.
However, in 2014 we found a creek dotted with the bodies of cane toads that had clearly been attacked. Every morning we discovered up to five new dead toads with small, near-identical incisions down their chest in just a five-metre stretch of creek. What was using almost surgical precision to attack these toads?
Post-mortem analysis showed that in larger toads the heart and liver had been removed, and the gall bladder (which contains toxic bile salts) neatly moved outside the chest cavity. In medium-sized toads, besides the removal of the heart and liver, one or both back legs had been stripped of their toxic skin and the muscle also eaten.
The finding intrigued us enough to dissect waterlogged and rotting toad bodies in 40℃ heat. Using remote infrared camera footage and analysis of the bites left on the muscle, we found our clever attacker – the native water rat!
What kind of toads are rats eating?
While there have been anecdotal reports of water rats eating toads in Queensland and the Northern Territory, there were no published reports of this in Western Australia, where the toad was a more recent arrival.
We also didn’t know whether rats could tolerate the toad toxins, or were targeting non-toxic parts of the body. And we wanted to find out whether the rats were targeting small (and less toxic) toads, as some other rodent species do, or were deliberately going after larger toads which are a better source of food.
During our study we captured and measured more than 1,800 cane toads in just 15 days in the vicinity of the water rats’ creek. The vast majority, 94%, were medium-sized; 3.5% were small (less than 4cm long); and just 2.5% were large (greater than 10cm long).
But despite medium toads being far more common, three quarters of the dead toads we found were large, and the remainder were medium. No small toad bodies were found or observed being attacked.
While some species, such as keelback snakes and several birds (including black and whistling kites, and crows) can eat cane toads, there has been less evidence of mammals hunting this new type of prey and living to tell the tale.
Some rodents can eat small juvenile toads, but no rodents have been documented specifically targeting large toads. In our case, water rats preferred to eat large toads, despite medium-sized toads outnumbering them by 27 to 1.
We’re not sure whether water rats have very rapidly learned how to safely attack and eat cane toads, or if they are adapting a similar long-term hunting strategy that they may use to eat toxic native frogs.
Water rats are very well placed to pass on hunting strategies, as they care for their offspring for at least four weeks after they finish producing milk. This could help spread the knowledge of toad hunting across streams and creeks over time.
While this behaviour seems to be confined to local populations, if these tactics spread, water rats may be able to suppress toad populations when they reach water bodies – another small line of defence against this toxic killer.
Marissa Parrott, Reproductive Biologist, Wildlife Conservation & Science, Zoos Victoria, and Honorary Research Associate, BioSciences, University of Melbourne; Sean Doody, Conjoint Fellow, University of Newcastle, and Simon Clulow, MQ Research Fellow, Macquarie University
Each year, from September to mid-October, the tiny and very precious mountain pygmy-possums arise from their months of hibernation under the snow and begin feasting on billions of bogong moths that migrate from Queensland to Victoria’s alpine region.
But for the past two springs, moth numbers have collapsed from around 4.4 billion in alpine areas to an almost undetectable number of individuals. And the mountain pygmy-possums went hungry, dramatically affecting breeding success among the last remaining 2,000 that live in the wild.
This year’s migration of bogong moths to the possums’ alpine home is crucial for the critically endangered mountain pygmy-possums. That’s why we’re asking you to do two simple things: turn off your lights at night, and if you see a bogong moth, take a picture.
What’s happened to the moths?
We don’t know exactly why the moths are not making it to their summer alpine destination. It’s likely extreme drought, pesticides and changes in agricultural practices are all major factors. However, scientists believe that because moths use both the Earth’s magnetic field and visual cues on the horizon to navigate, light pollution from urban centres can confuse the moths and stall their journey.
Some of the greatest beacons on their path are Parliament House and Canberra’s bright surrounds. Both parliamentarians and the general public are being asked to turn unnecessary outdoor lights off from September 1 to October 31, as part of the Lights Off for Moths campaign.
Artificial night lighting has dramatically changed the nocturnal environment. In urban environments, the soft glow of moonlight is overpowered by bright streetlights, security lights and car headlamps. These light sources can be more than 1,000 times as bright as moonlight, and their biological impact is increasingly visible and widespread.
One of the most obvious impacts of artificial light at night is that it can attract animals (sometimes fatally). While a “moth to a flame” may be somewhat poetic, when one moth becomes hundreds, or potentially thousands, the ecological impact may be catastrophic. Current global lighting practices may be creating this very scenario.
Recent evidence links the presence of artificial light at night with large-scale deaths and shifts in nocturnal migration patterns in birds. In insects, artificial night lighting disrupts nocturnal pollination networks and is strongly linked with observed mass declines in insect (and particularly moth) populations.
No moths means hungry possums
When a species like bogong moths decline, it has huge ramifications. Insects in particular are vital pillars supporting whole ecosystems – without bees and other insect pollinators, for example, we risk the extinction of our flowering plants. Many birds, reptiles and mammals depend on insects as part of their diet.
For mountain pygmy possums, the fatty, nutrient-rich bounty of bogong moths arrives right as they are waking up in the spring. They are one of the only Australian mammals that hibernate, and can spend up to seven months sleeping under the alpine snow.
The possums awake ravenously hungry, and devour the bogong moths to regain crucial fat stores. Without the moths there at the right time, the possums struggle to secure enough energy to breed successfully.
Snap that moth
Alongside the Lights Off for Moths campaign, Zoos Victoria has launched Moth Tracker, an app that allows Australians to photograph and log any potential sightings of migrating bogong moths.
Moth Tracker, which can be accessed through any laptop or smartphone, is adapted from the popular Southern Right Whale watching app in collaboration with Federation University and Victorian conversation network SWIFFT.
Bogong moths migrate from their winter breeding grounds throughout Queensland, New South Wales and western Victoria in search of cooler climates for the spring and summer in the Victorian and NSW Alpine regions where the mountain pygmy-possums live.
Before they become moths, the larvae look like tiny, shiny brown capsules and are commonly referred to as cutworm. Migratory bogong moths are dark brown, with two lighter spots on each wing. They are small, only about the length of a paper clip. During the day they’re often seen grouped together like roof tiles. At night, they are more active and flying around.
If you see a bogong moth (or something you think might be a bogong month), we need you to take a photograph and log the location, day and time with Moth Tracker. Scientists will use the data to determine whether any moths are making their way to the precious, and very hungry, possums that are just starting to wake from their winter hibernation.
The Victorian Mountain Pygmy-possum Recovery Team, together with partner organisations, is also investigating options for interventions in the wild if needed. These may include a world-first airdropping of “bogong balls” to feed the hungry possums, as well as improving habitat connectivity and captive measures to support populations through the breeding season.
But with unnecessary outdoor lights switched off and citizen scientists looking out for bogong moths, there is still hope for the mountain pygmy-possums.