Swift parrots are icons of Tasmania’s old-growth forests, but they’re also pretty tricky to find. These highly nomadic birds settle in a different place each year to breed, leaving nesting sites deserted for years between breeding events. This mobility makes them fascinating to study, but a nightmare to conserve.
Despite their elusive nature, we know enough about swift parrots to know they are under grave threat, particularly from Tasmania’s highly politicised logging industry.
In the context of ongoing habitat loss to logging, swift parrots were listed as critically endangered, because of the impact of another surprising factor: predatory sugar gliders, an introduced species to Tasmania.
About half of the female swift parrots that attempt to nest in Tasmania are eaten by sugar gliders each year. This alone could be enough to wipe out swift parrots within three generations. To try and combat this, we are aiming to install mechanical doors on swift parrots’ nest boxes, which close at night to stop the nocturnal sugar gliders getting in.
Ongoing logging makes the issue even more pressing. Nests seem to be more vulnerable to sugar glider predation if nearby areas have been logged. This means that the ongoing deforestation from logging is likely to make the parrots’ plight even worse by both reducing available habitat and worsening predation risk.
Protecting swift parrots is hard, because a truly effective strategy will require both large-scale habitat protection across Tasmania, and small-scale action such as our interventions against sugar glider predation.
The hot, dry Australian desert may not come to mind as an ideal location for waterbirds to breed, but some species wait years for the opportunity to do just that.
New research has shed light on one of Australia’s most enigmatic birds, the banded stilt. This pigeon-sized shorebird has long been a source of intrigue due to its bizarre and extreme breeding behaviour. They fly hundreds or thousands of kilometres from coastal wetlands to lay eggs that are 50-80% of their body mass in normally dry inland desert salt lakes, such as Lake Eyre, on the rare occasions they are inundated by flooding rain.
Such behaviour has been a mystery for decades; described for the first time in 1930, just 30 breeding events had been documented for the entire species in the following 80 years.
To investigate this behaviour, and to assess the stilts’ conservation status, we began a study in 2011, during which I was based in outback South Australia, ready to jump into a small plane after every large desert rainfall. We also satellite-tagged nearly 60 banded stilts, using miniature solar powered devices around half the size of a matchbox.
The research revealed that, on average, banded stilts respond within eight days to unpredictable distant flooding of outback salt lakes. They leave their more predictable coastal habitat to travel 1,000-2,000km in overnight flights to arrive at the newly flooded lakes and take advantage of freshly hatched brine shrimp.
Brine shrimp eggs lie dormant in the lakes’ dry salt crust for years or decades between floods, but upon wetting they hatch in their billions, creating a “brine shrimp soup” – a rich but short-lived banquet for the nesting stilts.
During the six-year study, we detected this nomadic movement and nesting behaviour seven times more often than it had been recorded in the previous 80 years. Although the banded stilts were previously thought to require large once-in-a-decade rains to initiate inland breeding, we found that small numbers of banded stilts respond to almost any salt lake inundation, arriving, mating and laying eggs equivalent of 50-80% of their body weight, despite high chances of the salt lake water drying before the eggs could hatch or chicks fledge.
Many times the eggs were abandoned as salt lake water dried. On other occasions some chicks survived long enough to learn to fly – although late-hatching chicks ran out of food or water and starved.
Once we found out that stilts needed much less rain to breed than previously thought, we used satellite imagery to reconstruct the past 30 years of flooding for ten salt lakes in South and Western Australia.
These models showed that conditions have been suitable for breeding more than twice as often as breeding events have actually been recorded. It seems that stilts’ nesting behaviour is so remote and hard to predict that scientists have been missing half the times it has happened.
Threats to banded stilt survival
Salt lakes in northwestern Australia are vital for banded stilts’ breeding. Our satellite tracking showed that birds from across the continent can reach these lakes after rain. Satellite images also suggested these lakes fill with water much more frequently than southern breeding sites.
These lakes are also largely free of native silver gulls (the common seagulls seen around our cities), which are predators of stilt chicks.
But other southern Australian breeding lakes are dramatically affected by gull predation. In one instance, a colony of 9,500 pairs (around 30,000 eggs) had less than 5% of its chicks survive, despite abundant water and brine shrimp on offer. Observations made near the colony suggested that a chick was being eaten by gulls every two minutes. Nearly 900 chicks and 350 eggs were eaten in the 30 hours we watched the colony.
Unfortunately, even the lakes that are relatively gull-free are now under threat from human development, despite being in one of the most remote parts of the world. Lakes Disappointment, Mackay, Dora, Auld and others surrounding them in the Little Sandy and Great Sandy Deserts are the subject of plans for potash mining.
The most advanced plans relate to Lake Disappointment, where Reward Minerals plans to construct a series of drainage trenches and 4,000 hectares of evaporation ponds on the lake bed to harvest potash for use in fertilisers.
This action will create permanent brine pools in some parts of the lake, and prevent other areas from receiving any water. As surface water drains into evaporation ponds, it’s likely the first rains after a long dry spell will no longer prompt mass brine shrimp hatching. Without this brine shrimp “soup”, banded stilts cannot breed at the site.
Meanwhile, the coastal habitat that supports banded stilt for the rest of the year is also changing. Sites that are home to thousands of birds, such as parts of the Dry Creek Saltfields and Bird Lake in South Australia, have been drained in the past two years.
If both the stilts’ inland breeding and coastal refuges are under threat, how can they survive?
Lessons for managing mobile species
This research offers insight into the conservation of highly mobile species, which may travel hundreds or thousands of kilometres in a year. Banded stilts are listed as vulnerable in South Australia, but have no conservation rating in the four other states in which they are found.
Individual banded stilts appear to operate over vast spatial scales, crossing between state jurisdictions in single overnight flights. Their episodic breeding events are hard to find and even more difficult to manage. Between breeding events, long-lived adults depend on refuges around the country which are being impacted by human activity, including potentially longer, harsher dry periods from climate change into the future.
These birds epitomise adaptation to unpredictable changes in their environment, but habitat loss and a warming climate may threaten them as much as any other species.
The authors would like to acknowledge L. Pedler, M. Christie, B. Parkhurst, R. West, C. Minton, I. Stewart, M. Weston, D. Paton, B. Buttemer and the South Australian Department for Environment, Water and Natural Resources, and Western Australian Department for Parks and Wildlife._
Cats kill more than a million birds every day across Australia, according to our new estimate – the first robust attempt to quantify the problem on a nationwide scale.
By combining data on the cat population, hunting rates and spatial distribution, we calculate that they kill 377 million birds a year. Rates are highest in Australia’s dry interior, suggesting that feral cats pose a serious and largely unseen threat to native bird species.
This has been a contentious issue for more than 100 years, since the spread of feral cats encompassed the entire Australian mainland. In 1906 the ornithologist A.J. Campbell noted that the arrival of feral cats in a location often immediately preceded the decline of many native bird species, and he campaigned vigorously for action:
Undoubtedly, if many of our highly interesting and beautiful birds, especially ground-loving species, are to be preserved from total extinction, we must as a bird-lovers’ union, at no distant date face squarely a wildcat destruction scheme.
His call produced little response, and there has been no successful and enduring reduction in cat numbers since. Nor, until now, has there been a concerted effort to find out exactly how many birds are being killed by cats.
Counting the cost
To provide a first national assessment of the toll taken by cats on Australian birds, we have compiled almost 100 studies detailing the diets of Australia’s feral cats. The results show that the average feral cat eats about two birds every five days.
We conclude that, on average, feral cats in Australia’s largely natural landscapes kill 272 million birds per year. Bird-kill rates are highest in arid Australia (up to 330 birds per square km per year) and on islands, where rates can vary greatly depending on size.
We also estimate (albeit with fewer data) that feral cats in human-modified landscapes, such as the areas surrounding cities, kill a further 44 million birds each year. Pet cats, meanwhile, kill about 61 million birds per year.
Overall, this amounts to more than 377 million birds killed by cats per year in Australia – more than a million every day.
Which species are suffering?
In a related study, we also compiled records of the bird species being killed by cats in Australia. We found records of cats killing more than 330 native bird species – about half of all Australia’s resident bird species. In natural and remote landscapes, 99% of the cat-killed birds are native species. Our results also show that cats are known to kill 71 of Australia’s 117 threatened bird species.
Birds that feed or nest on the ground, live on islands, and are medium-sized (60-300g) are most likely to be killed by cats.
It is difficult to put a million-plus daily bird deaths in context without a reliable estimate of the total number of birds in Australia. But our coarse assessment from many published estimates of local bird density suggests that there are about 11 billion land birds in Australia,
suggesting that cats kill about 3-4% of Australia’s birds each year.
However, particular species are hit much harder than others, and the population viability of some species (such as quail-thrushes, button-quails and ground-feeding pigeons and doves) is likely to be especially threatened.
In Australia, cats are likely to significantly increase the extinction risk faced by some bird species. In many locations, birds face a range of interacting threats, with cat abundance and hunting success shown to increase in fragmented bushland, in areas with high stocking rates, and in places with poorly managed fire regimes, so cat impacts compound these other threats.
The threatened species strategy also prioritised efforts to control feral cats more intensively, eradicate them from islands with important biodiversity values, and to expand a national network of fenced areas that excludes feral cats and foxes.
But while fences can create important havens for many threatened mammals, they are much less effective for protecting birds. To save birds, cats will need to be controlled on a much broader scale.
We acknowledge the contribution of Russell Palmer (WA Department of Biodiversity Conservation and Attractions), Chris Dickman (University of Sydney), David Paton (University of Adelaide), Alex Nankivell (Nature Foundation SA Inc.), Mike Lawes (University of KwaZulu-Natal), and Glenn Edwards (Department of Environment and Natural Resources) to this article.
The drone market is booming and it is changing the way we use airspace, with some unforeseen consequences.
The uptake of remotely piloted aircraft (RPAs) has been swift. But despite their obvious benefits, concerns are growing about impacts on wildlife.
In our research we investigate whether regulation is keeping pace with the speed of technological change. We argue that it doesn’t, and we suggest that threatened species might need extra protection to ensure they aren’t harmed by drones.
Drones are useful tools for conservation biologists. They allow them to survey inaccessible terrain and assist with many challenging tasks, from seeding forests to collecting whale snot.
But researchers are also discovering that RPAs have negative impacts on wildlife, ranging from temporary disturbances to fatal collisions.
Disturbance from vehicles and other human activity are known to affect wildlife, but with the speed that drones have entered widespread use, their effects are only just starting to be studied.
So far, the regulatory response has focused squarely on risks to human health, safety and privacy, with wildlife impacts only rarely taken into account, and even then usually in a limited way.
It is not uncommon for regulatory gaps to arise when new technology is introduced. The rapid growth of drone technology raises a series of questions for environmental law and management.
We have reviewed evidence for wildlife disturbance and current drone policies and found that the law is playing catch-up with emerging technology.
This is particularly important in New Zealand, where many threatened species live outside protected reserves. Coastal areas are of particular concern. They provide habitat for numerous threatened and migrating species but also experience high rates of urban development and recreational activity. Different species also respond very differently to the invasion of their airspace.
Where “flying for fun” and pizza delivery by drone combine with insufficient control, there is potential for unanticipated consequences to wildlife.
RPA and red tape
When competing interests collide, regulation requires particular care. Any rules on RPAs need to cater for a wide range of users, with varying skills and purposes, and enable beneficial applications while protecting wildlife.
There are strong social and economic drivers for the removal of red tape. Australia and the United States have introduced permissive regimes for lower-risk use, including recreational activity. In New Zealand, RPAs are considered as aircraft and controlled by civil aviation legislation.
Wildlife disturbance, or other impacts on the environment, are not specifically mentioned in these rules and control options depend on existing wildlife law.
The lack of consideration of wildlife impacts in civil aviation rules creates a gap, which is accompanied by an absence of policy guidance. As a consequence, the default position for limiting RPA operations comes from the general requirement for property owner consent.
RPA and spatial controls
RPA operators wanting to fly over conservation land have to get a permit from the Department of Conservation, which has recognised wildlife disturbance as a potential issue.
On other public land, we found that local authorities take a patchy and inconsistent approach to RPA activity, with limited consideration of effects on wildlife. On private land, efforts to control impacts to wildlife depend on the knowledge of property owners.
Protection of wildlife from RPA impacts is further confounded by limitations of legislation that governs the protection of wildlife and resource use and development. The Wildlife Act 1953 needs updating to provide more effective control of disturbance effects to species.
Marine mammals get some protection from aircraft disturbance under species-specific legislation. Other than that, aircraft are exempt from regulation under the Resource Management Act, which only requires noise control for airports. As a result, tools normally used to control spatial impacts, such as protective zoning, setbacks and buffers for habitat and species are not available.
This makes sense for aircraft flying at 8,000m or more, but drones use space differently, are controlled locally, and generate local effects. It is also clear that equipment choices and methods of RPA operation can reduce risks to wildlife.
Keeping drones out of sensitive spaces
Dunedin City Council in New Zealand recently approved a bylaw banning drones from ecologically sensitive areas. This is a good start but we think a more consistent and universal approach is required to protect threatened species.
As a starter, all RPA operations should be guided by specific policy and made available on civil aviation websites, addressing impacts to wildlife and RPA methods of operation. In addition, we advocate for research into regulatory measures requiring, where appropriate, distance setbacks of RPA operations from threatened and at risk species.
Distance setbacks are already used in the protection of marine mammals from people, aircraft and other sources of disturbance. Setbacks benefit species by acting as a mobile shield in contrast to a fixed area protection.
Congestion of space is a condition of modern life, and the forecast exponential growth of RPA in the environment indicates that space will become even more contested in future, both in the air and on the ground. We argue that stronger measures that recognise the potential impacts on wildlife, how this may differ from species to species, and how this may be concentrated in certain locations, are required to deliver better protection for threatened species.
With fewer than 160 birds alive, kākāpō are critically endangered. One reason for their dwindling numbers is that they only breed every few years, when native trees produce masses of edible fruit or seeds.
Our research suggests that the birds’ breeding success depends on oestrogen-like hormones (phytoestrogens) found in these native plants.
Hormone boost from plants
Our study included kākāpō (Strigops habroptilus) and two other New Zealand native parrots, the endangered kākā (Nestor meridionalis) and kea (Nestor notabilis). All three have infrequent breeding success.
Kākāpō in particular have a low reproductive rate and together with the kākā, only breed successfully every three or four years, during mast years, when mass fruiting of native trees occurs.
2016 was a mast year and a record breeding season for kākāpō – the best since New Zealand’s Department of Conservation began managing and monitoring the night parrots 25 years ago.
This link between the parrots’ successful breeding and high levels of fruiting in native plants has focused our investigations on potential stimulants present in their food plants that might activate or improve reproduction.
One hypothesis is that steroid-like compounds in the fruits of certain native plants provide a trigger for breeding. It proposes that kākāpō don’t produce enough of the hormone oestrogen to make a fertile egg, but by eating these fruits and the phytoestrogens they contain, the birds supplement their own hormone levels.
This increases the production of egg yolk protein, which in turn leads to eggs that have a better chance of being fertilised successfully.
We know from other studies that kākāpō seek out the fruit from the native rimu tree (Dacrycarpus cupressinum) during mast years. We believe that this is how kākāpō get extra oestrogen from their diet, and that rimu and other native plants provide a hormone boost that is key to kākāpō reproduction.
Parrots more sensitive to oestrogen
In our current study, conducted by PhD graduate Dr Catherine Davis, we examined the receptivity of New Zealand and Australian parrots to a range of steroid compounds, including oestrogens, and compared it to those of other birds.
We tested various native plant species for oestrogenic content and we found that indeed there is a high amount of phytoestrogens in some of New Zealand’s native plants.
We then looked at the receptivity of parrots to this plant hormone. We studied the genetic makeup of the receptor that is activated by oestrogens in kākāpō, kea, kākā, kākāriki, the Australian cockatiel, and compared this with those in the chicken.
We found that the parrots’ oestrogen receptor was different. All of the parrot species have a unique sequence in the receptor gene, which may make them more sensitive to oestrogen, compared to other bird species, or humans.
In parrots, this receptor contains an extra eight amino acids in the region that binds the hormone.
By adding this amino acid sequence to a computer modelling programme based on the human oestrogen receptor, we have shown that this difference in the parrot-specific receptor would change the strength with which it binds to the oestrogen hormone.
The down-stream effects of this may be an increased sensitivity to plant oestrogens in parrots. This research supports the notion that the parrots’ oestrogen receptor responds differently to oestrogenic compounds in native trees in New Zealand during mast years.
We have previously confirmed the presence of oestrogenic activity in key compounds present in rimu and tōtara (Podocarpus totara), as well as extracts from a number of New Zealand plant species that kākāpō are known to graze. However, the chemical structures of the oestrogenic materials of most New Zealand native plants are not known.
The question remains why the rate of successful breeding of kākāpō in mast years is lower than that of other parrot species. The identification of plant chemicals capable of binding to the parrot oestrogen receptor together with information about plant grazing behaviours of parrots may provide new insights into the conservation of the species that are in decline.
With further research, we are hoping to identify the specific compound in native plants that elicits these oestrogenic properties. This information may enable us to synthesise this compound in the lab. It could then be administered in some way to increase the fertility of our native parrots.
The word “pigeon” evokes thoughts of gentle cooing, fluttering in rafters, and poo-encrusted statues. The species responsible for the encrustation is deeply familiar to us, having ridden waves of European expansionism to inhabit every continent, including Australia. First domesticated thousands of years ago, urban pigeons have turned feral again.
Less familiar are the native species that are not your stereotypical pigeons: a posse of pointy-headed crested pigeons in a suburban park, or a flock of topknot pigeons feeding in a camphor laurel.
The future of Australia’s native pigeons however, may depend on our domestic pigeons. Australia’s domestic pigeon population — both feral and captive – is large and interconnected by frequent local and interstate movements. Pigeon racing, for example, involves releasing captive birds hundreds of kilometres from their homes only so they may find their way back. While most birds do navigate home, up to 20% will not return, of which some will join feral pigeon populations. Birds are also traded across the country and illegally from overseas. These movements, together with poor biosecurity practices, mean that captive pigeons can and do mingle with feral domestic pigeons.
And here’s a paradox. Could Australia’s feral domestic pigeons become the vector for a dramatic decline of columbids – native species on which Australian ecosystems rely?
Emerging viral epidemics
In recent years, two notable infectious diseases have been found to affect our captive domestic pigeons: the pigeon paramyxovirus type 1 (PPMV1) and a new strain of the pigeon rotavirus (G18P). These diseases are notable because in captive domestic flocks they are both spectacularly lethal and difficult to control.
PPMV1, although likely to have originated overseas, is now endemic in Australia. This virus has jumped from captive to feral domestic pigeon populations on several occasions, but fortunately has yet to establish in feral populations.
The movements of captive pigeons, and their contact with their feral counterparts, can be the route through which virulent and lethal diseases – such as the PPMV1 and the G18P – may spread to Australia’s native columbids.
What have we got to lose?
Fortunately, neither PPMV1 nor G18P has crossed over to Australia’s native columbids. We can’t say how likely this is, or how serious the consequences would be, because we have not previously observed such viral infections among our native pigeons.
If the viruses prove equally lethal to native columbids as they are to domestic pigeons, we could see catastrophic population declines across numerous columbid species in Australia over a short period of time.
Should these viruses spread (via feral domestic pigeons), the control and containment of losses among our native pigeon species would be near impossible. Such a nightmare scenario can only be avoided by predicting if and how these viruses might “spill over” into wild columbids so that we can prevent this in the first place.
Protecting our pigeons
Agricultural poultry is routinely screened to check their vulnerability to threats like the PPMV1 and G18P. Such screening is an appropriate response to protect our agricultural industry.
For our native pigeons and doves however, no such similar testing is planned. Based on progress in veterinary vaccine development and advancements in understanding of feral pigeon control, the knowledge and technology required to mitigate this threat should be relatively inexpensive. The threat for these species can be actively managed, now, by improving our biosecurity and vaccination programs for captive domestic pigeons, and eradicating feral domestic pigeons.
The protection of our native columbids however, ultimately relies on valuing their ecosystem functions in the first place.