For more than a decade, sugar gliders have been regarded as one of the greatest threats to the survival of Tasmania’s critically endangered swift parrot.
Since 2014, a series of influential studies has linked the introduced marsupial to high rates of nest failure and breeding female mortality, shaping conservation policy and efforts to manage predation across the swift parrot’s breeding range. Now, new field research is prompting researchers to re-examine parts of that long accepted understanding, suggesting the story may be more complex than first believed.
But the emerging debate is not simply a question of old research being right or new research proving it wrong. The evidence tells a far more interesting story, one that has developed over more than a decade and continues to change as new questions are asked and new findings emerge.
How Sugar Gliders Came to Tasmania
Sugar gliders (Petaurus breviceps) were deliberately introduced to Tasmania during the early nineteenth century, with historical records indicating they arrived near Launceston around 1835. Native to mainland Australia, New Guinea and parts of Indonesia, they had never naturally occurred on the island. Historical accounts suggest they were brought from the Port Phillip region as pets, although the precise circumstances surrounding their release into the wild remain uncertain.
There is also a small taxonomic twist to the story. While the Tasmanian population has traditionally been identified as the sugar glider (Petaurus breviceps), more recent taxonomic research has separated some Australian populations previously grouped under that name. As a result, some contemporary sources now identify Tasmania’s introduced gliders as Krefft’s glider (Petaurus notatus). The name sugar glider remains widely used in Tasmania and throughout much of the swift parrot research discussed in this article, so it is retained here for consistency.
The introduced population established successfully. Over the following decades, sugar gliders gradually expanded throughout much of eastern and northern Tasmania. Today, they occupy a wide range of eucalypt forests and woodlands where tree hollows provide shelter and breeding sites. Although they remain largely absent from western Tasmania, their distribution overlaps extensively with that of many native hollow dependent species, including the critically endangered swift parrot.
For more than 150 years, sugar gliders attracted relatively little attention as a major conservation threat in Tasmania. They were recognised as an introduced species, but there was little evidence to suggest they were having a significant ecological impact. That changed dramatically when researchers studying the breeding success of the critically endangered swift parrot made an unexpected discovery inside the birds’ nesting hollows.
How Did Sugar Gliders Become Linked to Swift Parrots?
The unexpected discovery emerged from research into swift parrot breeding success across Tasmania. Using motion activated cameras and regular nest inspections, ecologist Dejan Stojanovic and colleagues from The Australian National University documented sugar gliders entering occupied nest hollows, with subsequent inspections revealing that eggs and, in many cases, the adult female had been killed and eaten.
The observations challenged existing understanding of why swift parrot nests were failing. The cameras recorded several other species investigating swift parrot nests, but sugar gliders were the only animals documented successfully overcoming the physical protection provided by the hollows and causing predation during the study.
For the first time, researchers had documented sugar gliders preying on adult swift parrots, revealing a threat that had previously gone unrecognised. The discovery was particularly significant because female swift parrots spend extended periods inside tree hollows while incubating eggs and caring for newly hatched chicks. Predation therefore had the potential to result not only in the loss of eggs or nestlings, but also the breeding female herself.
The findings fundamentally changed the direction of swift parrot research. They suggested that breeding females, rather than just their eggs or chicks, could be lost during the nesting season, raising an important new question: how much of the species’ long term decline could be attributed to predation by introduced sugar gliders?
What Did the Original Research Actually Find?
The discovery of sugar glider predation in 2014 became a major new focus within an already growing body of research into the swift parrot’s decline. Over the years that followed, a broader evidence base emerged through field observations, habitat modelling, population genetics and management trials, with each study adding another piece to the conservation picture.
The foundational study was Discovery of a Novel Predator Reveals Extreme but Highly Variable Mortality for an Endangered Migratory Bird, by Dejan Stojanovic, Matthew Webb, Robert Heinsohn and colleagues. Over three breeding seasons, researchers monitored 70 nests across Tasmania using motion activated cameras and nest inspections. They recorded 24 predation events, with breeding females killed in more than 80 per cent of those attacks. The study also found that nest survival was dramatically lower in areas where sugar gliders occurred, while no nest failures were recorded on Bruny Island, where sugar gliders were absent.
Other work from the same research program was also building a clearer picture of the swift parrot’s unusual breeding ecology. In 2014, Location Matters: Using Spatially Explicit Occupancy Models to Predict the Distribution of the Highly Mobile, Endangered Swift Parrot showed that swift parrots shift their breeding distribution across Tasmania in response to the changing availability of flowering eucalypts. This meant the proportion of birds breeding within the sugar glider’s range could vary substantially from one season to the next.
In 2015, A Severe Predator-Induced Population Decline Predicted for Endangered, Migratory Swift Parrots used population viability modelling to estimate the possible consequences of that exposure. Across the mainland Tasmanian sites included in the study, 50.9 per cent of nesting females were killed by sugar gliders, compared with no recorded sugar glider predation on offshore islands. Its models predicted a population decline of between 78.8 and 94.7 per cent over three generations if the measured demographic conditions continued.
That modelling relied on the assumption that swift parrots formed a single interbreeding population rather than separate populations associated with different breeding areas. In 2018, Genetic Evidence Confirms Severe Extinction Risk for Critically Endangered Swift Parrots: Implications for Conservation Management tested that assumption and found no meaningful genetic subdivision across the breeding range. This strengthened the case that losses in areas experiencing high predation could have consequences for the species as a whole.
The research also began to test potential management responses. In 2021, Dejan Stojanovic and colleagues tested whether targeted sugar glider control could reduce nest predation. Their pilot field experiment, published as Evaluation of Lethal Control of Introduced Sugar Gliders as a Tool to Relieve Bird Nest Predation, found that reducing local predator numbers did not produce a measurable improvement in nest survival during the trial. Instead, the study highlighted the difficulty of translating ecological theory into practical conservation management and reinforced the importance of protecting and restoring suitable breeding habitat alongside any predator management.
Taken together, the research substantially changed scientific understanding of the threats facing the swift parrot. Habitat loss remained an important conservation concern, but sugar glider predation was now implicated not only in nest failure, but in the mortality of breeding females and potentially severe population decline. Those findings would go on to influence conservation policy and become incorporated into Australia’s National Recovery Plan for the Swift Parrot.
Why Are Scientists Re-examining the Evidence?
More than a decade after the original studies were published, researchers have continued to examine what is driving the swift parrot’s decline and how the different threats facing the species should be weighed against one another. Sugar glider predation has been directly documented, but questions remain about how predation, habitat loss and other pressures interact across a breeding range that can change considerably from one year to the next.
Those questions were examined in detail in 2026, when Tasmanian ecologist Simon Grove published What Is Driving the Continued Decline of Critically Endangered Swift Parrots? A Re-examination of the Research Papers. Rather than presenting new field data, Grove critically reviewed more than a decade of published research relevant to the swift parrot’s decline.
Grove compared two competing explanations within the conservation debate. One places greater emphasis on habitat loss, particularly the loss of nesting and foraging habitat associated with native forest harvesting, while the other identifies predation of nesting females, eggs and nestlings by introduced sugar gliders as the principal driver of decline. After reviewing the available research, Grove concluded that the evidence more strongly supported the predation explanation.
His conclusions were unequivocal. Grove argued that protecting existing breeding habitat alone would make little difference to the swift parrot’s immediate trajectory if birds continued to be killed while nesting. He instead called for much greater emphasis on finding practical ways to reduce sugar glider predation at scale, describing predation mitigation as the only strategy with the potential to prevent the species from becoming extinct.
What Does the New Research Add?
The latest research, led by landscape ecologist Matt Webb and veterinary ecologist Leanne Wicker, approaches the question from a different perspective. Rather than re-examining previously published studies, the team returned to the field to investigate contemporary interactions between swift parrots, sugar gliders and other species across the 2024/25 and 2025/26 breeding seasons.
The project combined large scale population monitoring with passive acoustic monitoring, motion activated cameras, glider surveys and investigations into the health and diet of both swift parrots and sugar gliders. This allowed the researchers to examine nesting outcomes within a broader ecological context rather than treating the presence of sugar gliders alone as an indicator of predation.
Across the two breeding seasons, sugar gliders were repeatedly detected visiting and entering occupied swift parrot nests, including nests that went on to successfully fledge young. Despite this activity, the researchers recorded no confirmed cases of sugar gliders preying on swift parrots during the intensive monitoring period. Their investigations of dead parrots and glider diets also found no evidence linking sugar gliders to the swift parrot deaths examined during the project.
Other species were documented interacting with nesting parrots. Black currawongs were observed taking chicks, while introduced European starlings attacked swift parrots and competed for nesting hollows. Yet no single species consistently determined whether a nest ultimately succeeded or failed. Instead, nest outcomes varied across sites and seasons, reinforcing the difficulty of attributing breeding failure to the presence of any one predator or competitor.
The findings do not show that sugar gliders pose no threat to swift parrots. Earlier predation events remain directly documented, including the deaths of adult breeding females. What the new research adds is evidence that sugar glider presence at a nest does not necessarily result in predation or nest failure, and that breeding success needs to be considered within a broader set of interacting ecological pressures.
Webb and Wicker place particular emphasis on habitat. Their findings consider predator and competitor interactions alongside the availability and condition of breeding habitat, food resources and suitable nesting hollows. Rather than treating habitat loss and predation as competing explanations for the swift parrot’s decline, the research points to the importance of understanding how these pressures interact and how their influence may change between landscapes and breeding seasons.
What Questions Still Need Answers?
Perhaps the most obvious question is also the most difficult to answer. Why did earlier studies document severe sugar glider predation at some swift parrot breeding sites, while the latest intensive field monitoring recorded no confirmed attacks across two breeding seasons despite gliders regularly visiting occupied nests?
Part of the answer may lie in the enormous variation between years and breeding locations. Swift parrots move their breeding activity around Tasmania in response to flowering conditions, meaning the birds, their predators and the habitats in which they interact are not necessarily the same from one season to the next. Longer term monitoring across a wider range of breeding sites will be important for establishing when, where and under what conditions sugar glider predation poses the greatest risk.
There are also important questions about what determines whether an individual nest succeeds or fails. Habitat condition, food availability, competition for suitable hollows and the abundance and behaviour of predators may all influence breeding success. Understanding how these pressures interact may help explain why outcomes can differ so substantially between nests, landscapes and breeding seasons.
And there remains a practical conservation question. If sugar glider predation is severe in particular places or under particular conditions, what is the most effective way to reduce it? The 2021 pilot trial of lethal sugar glider control did not produce a measurable improvement in swift parrot nest survival at the scale tested. Identifying interventions that genuinely improve breeding success, while continuing to address habitat loss and the other pressures facing the species, remains an important challenge.
What Does This Mean for the Swift Parrot?
The evidence leaves little doubt that sugar gliders can prey on swift parrots, including adult breeding females. More than a decade of research has shown how serious that predation can become under some conditions, and those findings have rightly influenced conservation planning for one of Australia’s most endangered birds.
The latest research does not erase that evidence. Instead, it adds observations that challenge us to understand why the relationship between sugar gliders and swift parrots can look so different between studies, landscapes and breeding seasons. Answering that question matters because conservation measures need to respond not simply to whether a threat exists, but to when, where and under what conditions it has the greatest impact.
There may ultimately be no single explanation that accounts for swift parrot breeding success across every landscape and every season. Habitat availability and condition, food resources, competition, predators and the movements of the parrots themselves can all shape the circumstances in which breeding takes place. Understanding how those pressures interact will be central to deciding where conservation effort can make the greatest difference.
Whatever the next studies reveal, the objective remains the same. Swift parrots need safe places to breed, sufficient habitat and food, and conservation measures that respond to the best available evidence about the threats they face.
Editorial Note: Wild Island is committed to publishing accurate, evidence based wildlife information. This article has been researched using authoritative sources, including government agencies, scientific institutions and peer reviewed literature. The information in this article was verified at the time of publication and will be updated if significant new evidence or guidance becomes available.
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