Before we knew it, autumn rolled in bringing more rain. Tragically, it led to widespread flooding across New South Wales, but elsewhere it helped to create more puddles. In our urban environments puddles are inconvenient: they can damage property and block our paths. But from a biological perspective, puddles are very important components of microhabitats and biodiversity.
We know for many animals — including birds and pets — puddles are a ready source of drinking water and provide a much-needed bath after a hot and dusty day. They’re also well known for providing water-reliant species such as mosquitoes with opportunities for breeding, and many of us may remember watching tadpoles developing in puddles as children.
But puddles make more nuanced and subtle contributions to the natural world than you may have realised. So with more rain soon to arrive, let’s explore why they’re so valuable.
Puddles are a diverse lot. They can be small or large, shallow or deep, long lasting or gone in a matter of hours. If you look closely at a puddle you will often find it is not even, especially on a slope.
Puddles consist of small, naturally formed ridges (berms) and depressions (swales). The berms form from silt and organic matter like leaf litter, which act as mini dams holding back the water in the swales behind them.
Berms and swales can be hard to see, but if you look closely they’re everywhere and contribute to the retention of water, affecting the depth, spread and the very existence of the puddle.
All of this means they meet the needs of different species.
On rainy days you may have seen birds such as magpies feeding on worms that wriggle to the surface. Worm burrows can be two to three metres deep and many species might come to the surface to feed on leaf litter.
Worms emerge during and after heavy rain when water floods their burrows and soil becomes saturated. The worms won’t drown but they do need oxygen, which is low in very wet soils.
Often in drier weather, getting a worm is not as easy as you might think — not even for the legendary early bird. So when heavy rain drives worms to the surface, it’s party time for birds that feed on them, and they make the most of the opportunity.
Swales in puddles often persist for days, which allows water-dependent insects to breed. Mosquito larvae, for instance, live in water for between four and 14 days, depending on temperature (so if you’re worried about mozzies, then remember puddles have to persist for days before the pesky pests emerge).
Tadpoles take between four and 12 weeks to develop into frogs, and requires a deeper, long-lasting puddle. But these puddles are becoming rarer in urban areas, and so it’s not often you see tadpoles or frogs in our suburbs.
Puddles also provide small, but important, reservoirs where seeds of many plant species germinate. In some cases, the seeds have chemical inhibitors in them, which prevent the seeds from germinating until after a period of heavy rainfall.
Then, the inhibitors are leeched from or diluted within the seeds, allowing them to germinate. Many desert species have this adaptation, including Australian eremophilas (emu bush).
In other cases, plants that grow all year round (annoyingly, weeds among them) need the dose of water puddles provide to kick start their very rapid growth and reproduction.
Easily germinated plants (such as tomatoes and cabbages) and ornamental flowering plants (such as hollyhocks and delphiniums) often require just a little extra water to trigger the whole germination process.
Puddles also provide more subtle opportunities for wildlife. Take Australia’s iconic river red gums (Eucalyptus camaldulensis) as an example. River red gums are water-loving trees that can withstand up to nine months of inundation without getting stressed.
What’s not so well known, however, is river red gums produce chemicals that rain washes from their leaves, accumulating beneath the tree. These chemicals can inhibit the growth of plants, such as weeds, under the canopies.
This effect — where chemicals produced by one plant have an effect on other plants — is called “allelopathy”. Many wattle species produce allelopathic chemicals and so do some important food plants, such as walnuts, rice and the common pea.
River red gum allelopathic chemicals can prevent the trees’ own seedlings from growing near them. So river red gums require floods to wash the chemicals from the soil away. This mechanism allows river red gums to germinate and regenerate when the soil is wet, and in places away from the competition of mature trees.
Puddles can do the same thing, on a small scale, ensuring trees have plenty of opportunities to persist in the wild. This pattern of regeneration is important to provide a mosaic of species and trees of different ages, making up a diverse range of habitats for other wildlife.
As property developers iron the creases from our created landscapes with much less open space and more paved surfaces, puddles are becoming harder to find close to home.
Taking away puddles removes a whole range of microhabitats, jeopardising the chances of a diverse range of species to breed and persist, especially in urban areas. These days, any loss of biodiversity is worrying.
So when you’re next out and about after or during heavy rain, keep an eye out for puddles.
Remember the life that depends on them and, if you can, try not to disturb them. Perhaps capture the joy of jumping over — rather than in — them. They are not just a nuisance, but a key to a nuanced and biodiverse local community.
Ross Crates, Australian National University; Dejan Stojanovic, Australian National University; Naomi Langmore, Australian National University, and Rob Heinsohn, Australian National UniversityJust as humans learn languages, animals learn behaviours crucial for survival and reproduction from older, experienced individuals of the same species. In this way, important “cultures” such as bird songs are passed from one generation to the next.
But global biodiversity loss means many animal populations are becoming small and sparsely distributed. This jeopardises the ability of young animals to learn important behaviours.
Nowhere is this more true than in the case of regent honeyeaters. In a paper published today, we describe how a population crash to fewer than 300 has caused the species’ song culture to break down.
In healthy populations, the song of adult male honeyeaters is complex and long. But where the population is very small, the song is diminished and, in many cases, the birds have adopted the song of other species. Sadly, this makes the males less attractive to females, which may increase the chance the regent honeyeater will become extinct.
Since 2015, we have monitored the regent honeyeater – a critically endangered, nectar-feeding songbird. The birds once roamed in huge flocks between Adelaide and Queensland’s central coast, tracking eucalyptus blossom.
As recently as the 1950s, regent honeyeaters were a common sight in suburban Melbourne and Sydney but are now extremely rare in both cities.
Extensive postwar land clearing has destroyed regent honeyeater habitat and caused the population to plummet. Most breeding activity is now restricted to the Blue Mountains and Northern Tablelands in New South Wales.
Regent honeyeaters are most vocal during the early stages of their breeding season. Before the population decline, the birds were known for their soft, warbling song produced with characteristic head-bobbing. But with few birds left in the wild, their song is changing – with potentially tragic consequences.
Song-learning is often completed in first year of life, after which a birds’ song is “fixed”.
Despite the increasing number of endangered bird species, there is surprisingly little research into how declines in population size and density might damage song culture in wild birds. We sought to explore whether this link existed in regent honeyeater populations.
Male regent honeyeaters sing to secure breeding territories and attract mates. We classified the songs of 146 male regent honeyeaters between 2015 and 2019. We made or obtained high-quality recordings of 47 of these in the wild, and more in captivity. This included wild birds found by the general public and reported to BirdLife Australia. We quickly chased up these public sightings to record the birds’ songs before they moved on.
Our research showed the songs of remaining wild males vary remarkably across regions. For example, listen to the “proper” song of regent honeyeaters occurring in the Blue Mountains west of Sydney, where most of the remaining population occur:
You’ll notice they sound noticeably different to the small number of males hanging on 400km to the north, near Glen Innes. Although these males still sound like a regent honeyeater, their songs are slower and have a different melody:
Across the species’ entire range, we found 18 males whose songs sounded nothing like a regent honeyeater. Instead, they closely resembled those of other bird species. Five male regent honeyeaters had learned the song of the little wattlebird:
Four males had learned songs of the noisy friarbird. Others sounded like pied currawongs, eastern rosellas or little friarbirds:
There are isolated cases of individual songbirds mistakenly learning the song of a different species. But to find 12% of males singing only other species’ songs is unprecedented in wild animal populations.
We believe regent honeyeaters are now so rare in the landscape, some young males are unable to locate adult males from which to learn their song. Instead, the young males mistakenly learn the songs of different bird species they’ve associated with when developing their repertoires.
Evidence suggests this song behaviour is distinct from the mimicry common in some Australian birds. Mimicry involves a bird adding the songs of other birds to its own repertoire – and so, not losing its original song. But the regent honeyeaters we recorded never sang songs that resembled that of their species.
Also, mimicry in other species has typically evolved because it increases breeding success. However in regent honeyeaters, we found the opposite. Even among males that sounded like a regent honeyeater, those whose songs were unusual for the local area were less likely to impress, and be paired with, a female. Females that did couple up to males with unusual songs were less likely to lay eggs.
These data suggest the loss of song culture is associated with lower breeding success, which could be exacerbating regent honeyeater population decline.
A captive-breeding program is a key component of the regent honeyeater recovery plan. However our research showed the songs of captive-bred regent honeyeaters were shorter and less complex than their wild counterparts:
This may affect the breeding success of captive-bred males once they’re released to the wild. Consequently, we’re teaching captive juveniles to sing correctly by playing them our recordings of “proper” songs from wild birds in the Blue Mountains.
Maintaining animal cultures in both wild and captive populations is increasingly recognised as crucial to preventing extinctions. These cultures include not just song, but also other important behaviours such as migration routes and feeding strategies.
The loss of the regent honeyeater song culture may be a final warning the species is headed for extinction. This is an aspect of species conservation we can’t ignore.
We must urgently restore and protect breeding habitats, protect nests from predators and teach captive-bred birds to sing. We must also address climate change, which threatens the species’ habitat. Otherwise, future generations may never hear the regent honeyeater’s dulcet tones in the wild.
Ross Crates, Postdoctoral fellow, Australian National University; Dejan Stojanovic, Postdoctoral Fellow, Australian National University; Naomi Langmore, Research Fellow, Australian National University, and Rob Heinsohn, Professor of Evolutionary and Conservation Biology, Australian National University
Environmental scientists see flora, fauna and phenomena the rest of us rarely do. In this new series, we’ve invited them to share their unique photos from the field.
Each year, oystercatchers, plovers and terns flock to beaches all over Australia’s coastline to lay eggs in a shallow scrape in the sand. They typically nest through spring and summer until the chicks are ready to take flight.
Spring and summer, however, are also when most people visit the beach. And human disturbances have increased breeding failure, contributing to the local contraction and decline of many beach-nesting bird populations.
Take Australian fairy terns (Sternula nereis nereis) in Western Australia, the primary focus of my research and photography, as an example. Their 2020-21 breeding season is coming to an end, and has been relatively poor.
Fox predation and flooding from tidal inundation wiped out several colonies. Unfathomably, a colony was also lost after a four-wheel drive performed bog-laps in a sign-posted nesting area. Unleashed dogs chased incubating adults from their nests, and photographers entered restricted access sites and climbed fragile dunes to photograph nesting birds.
These human-related disturbances highlight the need for ongoing education. So let’s take a closer look at the issue, and how communities and individuals can make a big difference.
Beach-nesting birds typically breed, feed and rest in coastal habitats all year round. During the breeding season, which varies between species, they establish their nests above the high-water mark (high tide), just 20 to 30 millimetres deep in the sand.
Some species, such as the fairy tern, incorporate beach shells, small stones and organic material like seaweed in and around the nest to help camouflage their eggs and chicks so predators, such as gulls and ravens, don’t detect them easily.
While nests are exposed and vulnerable on the open beach, it allows the birds to spot predators early and to remain close to productive foraging areas.
Still, beach-nesting birds live a harsh lifestyle. Breeding efforts are often characterised by low reproductive success and multiple nesting attempts may be undertaken each season.
Many historically important sites are now so heavily disturbed they’re unable to support a successful breeding attempt. This includes the Leschenault Inlet in Bunbury, Western Australia, where fairy tern colonies regularly fail from disturbance and destruction by four-wheel drives.
Birds see people and dogs as predators. When they approach, nesting adult birds distance themselves from the nest and chicks. For example, terns typically take flight, while plovers run ahead of the threat, “leading” it away from the area.
When eggs and chicks are left unattended, they’re vulnerable to predation by other birds, they can suffer thermal stress (overheating or cooling) or be trampled as their cryptic colouration makes them difficult to spot.
Unlike plovers and oystercatchers, fairy terns nest in groups, or “colonies”, which may contain up to several hundred breeding pairs. Breeding in colonies has its advantages. For example, collective group defence behaviour can drive off predatory birds such as silver gulls (Chroicocephalus novaehollandiae).
However, this breeding strategy can also result in mass nesting failure. For example, in 2018, a cat visiting a colony at night in Mandurah, about 70 km south of Perth, killed six adults, at least 40 chicks and led to 220 adult birds abandoning the site. In other instances, entire colonies have been lost during storm surges.
Land and wildlife managers are becoming increasingly aware of fairy terns and the threats they face. Proactive and adaptive management combined with a good understanding of early breeding behaviour is helping to improve outcomes for these vulnerable birds.
Point Walter, in Bicton, WA, provides an excellent example of how recreational users and beach-nesting birds can coexist.
Point Walter, 18 km from Perth city, is a popular spot for picnicking, fishing, kite surfing, boating and kayaking. It’s also an important site for coastal birds, including three beach-nesting species: fairy terns, red-capped plovers and Australian pied oystercatchers (Haematopus longirostris).
The end of the sand bar is fenced off seasonally, and as a result the past six years has seen the number of terns increase steadily. For the 2020-2021 season, the sand bar supported at least 150 pairs.
The closure also benefits the local population of red-capped plovers and Australian pied oystercatchers, who nest at the site each year.
What’s more, strong community stewardship and management interventions by the City of Mandurah to protect a fairy tern colony meant this season saw the most successful breeding event in more than a decade — around 110 pairs at its peak.
Interventions included temporary fencing, signs, community education and increased ranger patrols. Several pairs of red-capped plovers also managed to raise chicks, adding to the success.
These examples highlight the potential for positive outcomes across their breeding range. But intervention during the early colony formation stage is critical. Temporary fencing, signage and community support are some of our most important tools to protect tern colonies.
share the space and be respectful of signage and fencing. These temporary measures help protect birds and increase their chance of breeding success
keep dogs leashed and away from known feeding and breeding areas
avoid driving four-wheel drive vehicles on the beach, particularly at high tide
keep cats indoors or in a cat run (enclosure)
if you see a bird nesting on the beach, report it to local authorities and maintain your distance
avoid walking through flocks of birds or causing them to take flight. Disturbance burns energy, which could have implications for breeding and migration.
Picture this: you’re in your backyard gardening when you get that strange, ominous feeling of being watched. You find a grey oval-shaped ball about the size of a thumb, filled with bones and fur — a pellet, or “owl vomit”.
You look up and see the bright “surprised” eyes of a powerful owl staring back at you, with half a possum in its talons.
This may be becoming a familiar story for many Australians. We strapped tracking devices to 20 powerful owls in Melbourne for our new research, and learned these apex predators are increasingly choosing to sleep in urban areas, from backyard trees to city parks.
These respite areas are critical for species to survive in challenging urban environments because, just like for humans, rest is an essential behaviour to conserve energy for the day (or night) ahead.
Our research highlights the importance of trees on both public and private land for wild animals. Without an understanding of where urban wildlife rests, we risk damaging these urban habitats with encroaching development.
Powerful owls are Australia’s largest, measuring 65 centimetres from head to tail and weighing a hefty 1.6 kilograms. They’re found in Australia’s eastern states, except for Tasmania.
These owls have traditionally been thought to live only in large old-growth forested areas. However, Victoria has lost over 65% of forest cover since European settlement, and because of this habitat loss, the owls are listed as threatened in Victoria.
Their remaining habitat is extremely fragmented. This means we’re finding owls in interesting places — from dry, open woodland to our major east coast cities. This is likely due to the high numbers of prey, such as possums, that thrive alongside exotic garden trees and house roofs.
Powerful owls usually eat one possum per night, or 250-300 possums per year — mostly common ringtail and brushtail possums in Melbourne. They’re often seen holding prey at their roosting spots, where they’ll finish eating in the evening for breakfast.
This has ecosystem-wide benefits, as powerful owls can help keep overabundant possums in check. Too many possums can strip away vegetation, causing it to die back, which stops other wildlife from nesting or finding shelter.
But powerful owls are extremely elusive. With low populations, locating owls and researching their requirements is very difficult.
Over five years, we deployed GPS devices on 20 Melburnian owls to find how they use urban environments. These devices automatically record where the owls move at night and rest during the day.
We learned they fly, on average, 4.4 kilometers per night through golf courses, farms, reserves and backyards looking for dinner and defending their territory. One owl along the Mornington Peninsula travelled 47 km over two nights (possibly in search of a mate). Another urban owl called several golf courses in the Melbourne suburb of Alphington home.
After their nightly adventures, the owls usually return to a number of regular roosting (resting) spots, sometimes on the exact same branch. The powerful owl chooses roosts that protect them against being mobbed by aggressive daytime birds, such as the noisy miner and pied currawong.
We found the owls used 32 different tree species to roost in: 23 were native, and nine were exotic, including pine and willow trees. This shows powerful owls can adapt to use a range of species to fit their roosting requirements, such as thick foliage to hide in during the day.
Owls will generally roost in damp, dark areas during summer, and in open roosts in full or dappled sunlight during winter to help regulate their body temperature.
Our research also shows rivers in urban environments are just as important as trees for roosting habitat.
Rivers are naturally home to a diverse range of wildlife. Using trees near rivers to rest in may be a strategic decision to reduce time and energy when travelling at night to find other resources, such as prey, mates and nests.
Rivers that constantly flow, such as the Yarra River, are a particular favourite for the owls.
These resting habitats, however, are under constant pressure by urban expansion and agriculture. Suitable roosting habitat is either removed, or degraded in quality and converted to housing, roads, grass cover or bare soil.
We found potentially suitable roosting habitat in Melbourne is extremely fragmented, covering just 10% of the landscape because owls are very selective about where they sleep.
Although there might be the odd suitable patch (or tree) to roost in urban environments, what’s often lacking is natural connectivity between patches. While owls are nocturnal, they still need places to rest in the night before they settle down in another spot to sleep for the day.
Supplementing habitat with more trees on private property and enhancing the quality of habitat along river systems may encourage owls to roost in other areas of Melbourne.
Powerful owls don’t discriminate between private land and reserves for roosting. So conserving and enhancing resting habitats on public and private land will enable urban wildlife to persist alongside expanding and intensifying urbanisation.
If you want powerful owls to roost in your backyard, visit your local indigenous nursery and ask about trees local to your area.
Several favourite roost trees in Melbourne include many Eucalyptus species and wattles. If you don’t have the space for a large tree, they will also roost in the shorter, dense Kunzea and swamp paperbark (Melaleuca ericifolia).
Planting them will provide additional habitat and, if you are lucky, your neighbourhood owls may even decide to settle in for the day and have a snooze.
Australians have a love-hate relationship with sulphur-crested cockatoos, Cacatua galerita. For some, the noisy parrots are pests that destroy crops or the garden, damage homes and pull up turf at sports ovals.
For others, they’re a bunch of larrikins who love to play and are quintessentially Australian.
Along with other scientists, I had a unique opportunity during the COVID-19 lockdowns to study things that had intrigued me closer to home, perhaps for years. While isolating in the suburbs of Melbourne, I wanted to find out why cockatoos return to the same places, and what they’re after.
The answer? Onion grass, reams of it.
Onion grass is a significant weed, and I estimated in a recent paper that one bird gorges on about 200 plants per hour. A flock of about 50 birds can consume 20,000 plants in a couple of hours.
This significantly reduces the weed level and may make expensive herbicide use unnecessary. So if you have a large amount of onion grass on your property and are regularly visited by sulphur-crested cockatoos, it would be wise to let them do their weeding first.
Most of us see cockies whether we live in rural communities or major cities, but how much do you really know about them?
In late winter and early spring in many parts of Australia, flocks of sulphur–crested cockatoos can be seen grazing on the ground. They’re usually found close to water, nesting in woodlands with old hollow trees, such as river red gums, Eucalyptus camaldulensis.
Where these forests and trees are being cleared, the number of cockies falls. But they are resilient and adaptable birds, and have spread their range to cities and the urban fringe, where numbers are increasing.
The birds are known to play with fruits, hang upside down on branches or perform flying cartwheels by holding a small branch or powerline with their feet, flapping their wings as they do loop after loop.
Sometimes their play verges on vandalism as they follow tree planters, deftly pulling up just-planted trees and laying them neatly beside the hole.
While cockatoos feed on the fruits and seed of native species, they’ve adapted very quickly to the introduction of exotic species, such as onion grass from South Africa, which is plentiful and easy to harvest.
I observed flocks ranging from nine to 63 cockatoos at seven sites along the Maribyrnong River in Keilor last July and August. Onion grass was the only item on their menu.
Onion grass (Romulea rosea) is small and usually inconspicuous with grass-like leaves. It’s typically only noticed when it flowers in spring, producing pretty, pink and yellow-throated flowers.
Onion grass can be a serious weed that’s very difficult to control. It’s not only a problem for agricultural land, but also for recreational turf and native grasslands.
In some areas, there are nearly 5,000 onion grass plants per square metre. This is a massive number requiring costly control measures, such as spraying or scraping away the upper layer of top soil.
Onion grass gets its name from its onion-like leaves. At the base is a small bulb, which works as a modified underground stem called a “corm”. The corm is what cockatoos will travel many kilometres for, to dig up and return to for days on end.
Like other native parrots, sulphur-crested cockatoos are famously left-footed. So it was interesting to observe them primarily use their powerful beaks to pull onion grass plants from the ground and dig up corms, using their left foot only occasionally to manipulate the plant.
The cockatoos fed for between 30 minutes and two and a half hours. At each feed, one or two sentry (or sentinel) birds, depending on the flock size, would keep watch and give raucous warning should danger threaten.
The cockies could remove a plant and corm from the ground in as little as six seconds, but sometimes it could take up to 30 seconds. They then removed and consumed a corm every 14 seconds on average in wet soil and every 18 seconds from harder, dry soil.
This means a flock of 63 birds could remove more than 35,400 onion grass plants in a feeding session lasting two and half hours. This is a super weeding effort by any standard!
My further investigation revealed most of the corms were within 20 millimetres of the soil surface, so the holes left in the soil by the birds extracting the onion grass were shallow and quite small. This shouldn’t give seeds from onion grass any great advantage.
And they’re very efficient: the birds eat over 87% of the corms they lift, which then won’t get a chance to generate in future years. So, if we’re going to try to eradicate onion grass, it may be better to let the cockies do their work first before we humans take a turn.
We have a lot to learn about how our native species interact with introduced weeds, and more research might reveal some very useful future partnerships. They might be birdbrains, but sulphur-crested cockatoos really know their onions when it comes to, well, onion grass.
Plastic in the ocean can be deadly for marine wildlife and seabirds around the globe, but our latest study shows single-use plastics are a bigger threat to endangered albatrosses in the southern hemisphere than we previously thought.
We examined the causes of death of 107 albatrosses received by wildlife hospitals and pathology services in Australia and New Zealand and found ocean plastic is an underestimated threat.
Plastic drink bottles, disposable utensils and balloons are among the most deadly items.
Albatrosses are some the world’s most imperiled seabirds, with 73% of species threatened with extinction. Most species live in the southern hemisphere.
We estimate plastic ingestion causes up to 17.5% of near-shore albatross deaths in the southern hemisphere and should be considered a substantial threat to albatross populations.
Each year, thousands of albatrosses are caught as unintended bycatch and killed by fishing boats. Introduced rats and mice eat their chicks alive on remote islands and the ocean where they spend their lives is becoming increasingly warmer and filled with plastic.
Young Laysan albatrosses with their bellies full of plastic are not just a tragic tale from the remote northern Pacific. Albatrosses are dying from plastic in the southern oceans, too.
Eighteen of the world’s 22 albatross species live in the southern hemisphere, where plastic is currently considered a lesser threat. But the amount of discarded plastic is increasing every year, mostly leaked from towns and cities and accumulating near the shore.
When albatrosses are found struggling near the shore in New Zealand, they are delivered to wildlife hospitals such as Wildbase Hospital and The Nest Te Kōhanga. A recent spate of plastic-linked deaths spurred us to dig a little deeper into the risk of plastic pollution to these magnificent ocean wanderers.
Of the 107 albatrosses of 12 species we examined, plastic was the cause of death in half of the birds that had ingested it. In the cases we examined, plastic deaths were more common than fisheries-related deaths or oiling.
We compared these cases with data on plastic ingestion and fishery interaction rates from other studies. Based on our findings, we used statistical methods to estimate how many albatrosses were likely to eat plastic and might die from ingesting it, and how these figures compared to other major threats such as fisheries bycatch.
We found that in the near-shore areas of Australia and New Zealand, the ingestion of plastic is likely to cause about 3.4% of albatross deaths. In more polluted near-shore areas, such as those off Brazil, we estimate plastic ingestion causes 17.5% of all albatross deaths.
Because albatrosses are highly migratory, even those birds that live in less polluted areas are at risk as they wander the global ocean, travelling to polluted waters. Our results suggest the ingestion of plastic is at least of equivalent concern as long-line fishing in near-shore areas.
For threatened and declining albatross species, these rates of additional mortality are a serious concern and could result in further population losses.
Not all types of plastic are equally deadly when eaten. Albatrosses can regurgitate many of the indigestible items they eat.
Soft plastic and rubber items (such as latex balloons), in particular, can be deadly for marine animals because they often become trapped in the gut and cause fatal blockages, leading to a long, slow death by starvation. Plastic is difficult to see with common scanning techniques, and gut blockages often remain undetected.
We recommend that wildlife hospitals, carers and biologists consider gastric obstruction when sick albatrosses are presented. Our publication includes a checklist to help in the detection of gastric blockages.
Global cooperation to reduce leakage of plastic items into the ocean — such as the Basel Convention and the recommendations by the High Level Panel for a Sustainable Ocean Economy — are first steps towards preventing unnecessary deaths of marine animals.
Stronger adherence to multilateral agreements, such as the Agreement on the Conservation of Albatrosses and Petrels which aims to reduce the impact of activities known to kill albatrosses, would help prevent the decline of breeding populations to unsustainably low levels.
If populations fall to critically endangered levels, intensive remediation including the expansion of chick and nest protection programmes, invasive species eradication and seabird translocations, may be required to prevent species extinction.
We would like to acknowledge our New Zealand and Australian colleagues who contributed to this research project. Veterinarians Baukje Lenting and Phil Kowalski care for injured seabirds and other wildlife at The Nest Te Kōhanga at Wellington Zoo. Veterinarian Megan Jolly cares for injured wildlife at Wildbase Hospital and vet pathologist Stuart Hunter provides a nationwide wildlife pathology service at Wildbase pathology at Massey University. David Stewart conducts threatened species research and monitoring at the Queensland state government’s Department of Environment and Science.
Richelle Butcher, Veterinary Resident at Wildbase, Massey University; Britta Denise Hardesty, Principal Research Scientist, Oceans and Atmosphere Flagship, CSIRO, and Lauren Roman, Postdoctoral Researcher, Oceans and Atmosphere, CSIRO
Have you ever seen magpies play-fighting with one another, or rolling around in high spirits? Or an apostlebird running at full speed with a stick in its beak, chased by a troop of other apostlebirds? Well, such play behaviour may be associated with a larger brain and a longer life.
For the past 50 years, international animal cognition research has often related the use of tools such as rocks and sticks to cognitive abilities in animals. But my research on Australian native birds, published in Scientific Reports, casts doubt on long-held assumptions about the links between large brains and tool use.
My study found no significant association between tool use and brain mass. However, very clear differences in relative brain mass emerged when birds showing play behaviour were compared to those that didn’t play. In particular, birds that played with others (known as social play) had the largest brain mass, relative to body size, and even the longest lifespans.
The results suggest play behaviour may be an important driver in the evolution of large brains in a number of species, including humans.
Tool use has been studied in a wider range of species than play behaviour. Some internationally famous Australian examples include:
the black-breasted buzzard releasing rocks from their beaks to crack emu eggs
the black kite picking up burning embers and twigs and dropping them on dry grass areas to start a fire. The bird then feasts on fleeing or injured insects and vertebrates
palm cockatoos that drum with a stick.
According to a classic theory known as the “technical intelligence hypothesis”, humans and other animals developed large brains because circumstances forced them into ever more sophisticated tool use.
Play behaviour usually occurs in juveniles but in some species, such as little corellas or galahs, it extends into adulthood. Play behaviour occurs in species which tend to have long juvenile periods, long-term support from parents and which grow up in stable social groups.
Play behaviour is usually subdivided into three categories: solo play, object play and social play.
Solo play: this may involve a single bird running, skipping, jumping, ducking, rolling, hanging, swinging, dancing, sliding and snow-romping. Solo play is the most widespread form of play, common among honeyeaters, parrots, magpies, currawongs, butcherbirds, riflebirds and some pigeon species.
The best acrobat among the pigeons is probably the topknot pigeon, but rainbow lorikeets are also known to love swinging.
Object play: this involves objects of any kind, including sticks, stones and small household items. Object players might carry a stick or stone or even just a leaf around, drop it, then pick it up again and run with it.
Object players are not as numerous as solo players but still widespread across species. Click here to read a lovely description of a kookaburra absorbed in playing with a stone.
Social play: involves two or more individuals. Social play is so far the rarest category. It might involve one bird holding an object in its beak and the others chasing it. Published cases are largely limited to parrots and corvids, and are known in magpies and ravens.
White-winged choughs are known to play a game in which two youngsters simultaneously grab a small stick or a bunch of grass, then each tries to wrest it from the other.
It’s important to note that social players are also solo and object players, but solo or object players may not be social players. The latter is considered a more complex form of play.
It turns out these categories are meaningful when used to analyse a potential link to brain mass. Information on brain weight/mass in Australian birds has been available only since an important study in 2014. It identified brain volumes and body sizes of all Australian bird species, enabling researchers to link these biological data to behavioural data.
My study involved 77 native Australian bird species for which full data sets were available. The results were more than surprising. In the samples used, tool use seems to confer no advantage whatsoever in terms of brain size or life expectancy: no matter whether a species showed tool using or not, relative brain masses were not different. However the results showed, rather dramatically, that brain size and forms of play are associated.
Social players, versus other players and versus non-players showed significantly different average brain sizes in each category:
non players have the lowest average brain size
solo players had slightly larger brains than non-players
object players had larger brains again
social players had by far the largest average brain size relative to body weight.
These results are by no means confined to parrots, but are found in songbirds and other orders. Whether this holds for birds globally is not yet known. However, since parrots and songbirds first evolved in Australia, then spread to the rest of the world, the results may indeed hold for birds outside Australia. More research will be needed.
Which came first – play resulting in large brains or large brains triggering play behaviour – is not known. But whichever way one looks at it, playing socially or even just playing at all, is related to a bigger brain and a long life.
So what does all this mean for human brain evolution? It may be a long shot, but the stages of development in humans and birds seem to have some similarities and this may be significant.
Offspring in humans, as in great apes and other primates, also develop slowly, have protracted childhoods and play extensively as do a surprising number of Australian native birds. It may mean playing together offers more than just passing the time. It could be an evolutionary driver for intelligence, and even for a long life.