Science for Saving Species - Research findings factsheet Project 2.2.2
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Science for Saving Species
Research findings factsheet
Project 2.2.2
Sex ratio bias in swift parrots due to sugar glider
predation and implications for population viability
In brief
The swift parrot is listed as Critically The swift parrot is naturally socially Other key threats to the species
Endangered under the EPBC Act monogamous, but as there are include deforestation, habitat
and is in rapid decline. now estimated to be roughly three degradation from altered fire
males for every female, harassment regimes, timber harvesting, and
While swift parrot females are sitting
of already paired females by single climate change. Urgent and targeted
on eggs or chicks within nesting tree
males has become substantial. We management is needed to prevent
hollows they are highly vulnerable to
found that half (50.5%) of nests now the extinction of the species and will
predation by sugar-gliders where
have multiple fathers and this shared require coordinated protection of
the ranges of these two species
paternity is associated with reduced the species breeding and foraging
overlap. Intense predation of nesting
reproductive fitness in the species. habitat and management, where
females in these areas has led to
Interference of nesting females by possible, of introduced
biased sex ratios. It is estimated that
unpaired male swift parrots appears nest predators.
fewer than 1000 individual swift
to be reducing the number of chicks
parrots remain, and overall 73%
that successfully fledge per nest.
are estimated to be male.
Swift parrots. Image: Dejan Stojanovic
predict.
Swift parrots have highly specialised requirements for breeding: the co-occurrence of
eucalypts for food, and tree hollows suitable for nesting. Substantial areas of the swi
range overlap with areas used by the timber industry, and have been lost or disturbed
harvesting,
BELOW: Figureclearance and conversion,
1: Forest loss/disturbance and fire.
in Tasmania Population
between 1996 anddeclines
2016 (red)due
and to habitat los
potential swift parrot breeding range (yellow line). Forest loss was estimated from the
habitat can substantially exacerbate the impact of other threats, such as sugar gliders
Global Forest Cover change layer.
Background
The swift parrot (Lathamus discolor)
is listed as Critically Endangered
under the Environment Protection
and Biodiversity Conservation
(EPBC) Act 1999. The swift parrot
has been a species of conservation
concern since the 1980s. A national
recovery plan for the species was
prepared in 2002, which was
adopted under the EPBC Act.
The extinction risk for this species is
currently very high. An assessment
in 2018 found that there was a
one in three (31%) probability
that swift parrots would be
extinct within 20 years.
The species is in rapid decline due
to a range of factors, including
ongoing clearing of high-quality
breeding and foraging habitat, nest
predation by sugar gliders (Petaurus
breviceps), and habitat degradation
Figure 1: Forest
Substantial areasloss/disturbance
of the swift parrotin Tasmania
therebetween 1996 and 2016
was no predation, while (red)
44% and poten
from altered fire regimes, timber
breeding range (yellow line).
breeding range overlap with areas Forest loss was estimated from the Global
of mainland nests were predated Forest Cover c
harvesting and climate change.
used by the timber industry, and by sugar gliders, and in 83% of
Swift parrots breed in Tasmania in Predation by sugar gliders, which were introduced to Tasmania from the Australian m
have been lost or disturbed due to these cases the mother parrot
summer, and migrate to woodlands 19th century,
timber is a key
harvesting, threat to
clearance andthe swift was
parrot.
alsoWe monitored
killed 70 nests in seven regio
and eaten.
across south-eastern mainland breeding seasons (2011–12)
conversion, and fire. Population and found that sugar gliders eat eggs and young nestling
states for the rest of the year. The actual predation rate at
the female
declines dueparrot.
to habitat loss,
They feed mostly on the nectar mainland breeding sites varied
and degradation of habitat can
of eucalypt flowers. Across their substantially and was influenced
However, theexacerbate
substantially actual predation
the rate varies greatly depending on which region the swif
range, swift parrots follow flowering by the level of mature forest cover.
Bruny and
impact Mariathreats,
of other Islands,such
where sugar gliders arewith
At sites absent,
low there
forest was no 100%
cover, predation, whi
pulses in their favourite food trees. as sugar gliders.
Climatic variations can result in wide of monitored nests were predated,
variations in blue gum flowering Predation by sugar gliders, which while at sites with higher forest
from year to year. This means that were introduced to Tasmania from cover survival was much higher.
an area that is suitable one year may the Australian mainland as early as
Due to intense predation of nesting
not be suitable for several future the 19th century, is a key threat to
females by introduced sugar gliders,
years, and that swift parrots require the swift parrot. We monitored 70
swift parrots have a strongly male-
large amounts of habitat over the nests in seven regions across three
biased population. Skewed sex
long term. As variations in blue breeding seasons (2011–12) and
ratios can lead to harassment of
gum flowering are hard to predict, found that sugar gliders eat
the rarer sex which can in turn lead
the movements of swift parrots eggs and young nestlings, and
to their reduced fitness. It can also
are also hard to predict. commonly kill the female parrot.
lead to changes in mating patterns.
Swift parrots have highly specialised However, the actual predation rate This can have potentially severe
requirements for breeding: the varies greatly depending on which impacts for population viability
co-occurrence of preferred region the swift parrots nest in. and stability of a species but had
flowering eucalypts for food, and On Bruny and Maria Islands, not been previously examined
tree hollows suitable for nesting. where sugar gliders are absent, for swift parrots.
Research aims
We aimed to investigate factors affecting reproductive success in swift parrots and the implications of these for
the long-term conservation of the species, including population viability.
In particular, we examined whether the male-biased population of swift parrots has led to greater competition
for females and, consequently, changes in the mating system of the species.
This is part of a broader program of research aimed at reducing the very high extinction risk for swift parrots.
Figure 2. Map of the study area
What we did in Tasmania. Genetic samples
were collected from North
Over six years (2010–16) we
(BN) and South Bruny Islands
collected genetic samples of 371 (BS), Buckland (BU), Eastern
nestlings from 85 nests across a Tiers (ET), Meehan Range (ME),
range of forest types over most of Rheban (RH), Southern Forests
(SF) and Wielangta (WI).
the breeding range. We undertook
DNA extraction and genetic analysis
to classify genetic relatedness
and used two techniques for
detection of multiple paternity.
We compiled the mortality rates of
nesting females due to predation by
sugar gliders across the Tasmanian
breeding range of swift parrots.
We measured fledging success for
all monitored nests as the number
of nestlings expected to fledge.
We undertook population viability
analyses to examine the relationship
between predation, sex ratio bias
and extinction risk in the swift parrot.
Figure 2. Map of the study area in Tasmania. Genetic samples were collected from North (BN) and So
Key findings Bruny Islands (BS), Buckland (BU), Eastern Tiers (ET), Meehan Range (ME), Rheban (RH), Southern For
The predation of nesting females by (SF) and Wielangtato
according (WI).
the rate of • Shared paternity is associated
introduced sugar gliders has led to predation of breeding females, with reduced reproductive
changes in the mating patterns of Key findings
suggesting that rates of shared success in the species.
the swift parrot. These changes in paternity increased when the • Nests
turn have implications for individual The predation of nesting females by introduced sugar glidersthat hadtoshared
has led changespaternity
in the mating patter
adult sex ratio became more produced fewerfitness,
fledglings. This popula
the swift parrot. These changes in turn have implications for individual and long-term
fitness, and long-term population male-biased – i.e., on mainland
viability of swift parrots. could be a result of interference
viability of swift parrots. Tasmania. during the nesting period by
The main findings are: The
• main
This findings
rate ofare:
shared paternity is unpaired male swift parrots.
• Less than 1000 individual swift unusually high compared to • Modelling predicted that the
• Less than 1000 individual swift parrots remain, and overall 73% of these are male.
parrots remain, and overall most parrot species. Although population would decline by
• 50.5% of swift parrot nests had shared paternity overall, although the birds remained socially
73% of these are male. we do not know the extent 89.4% over three generations if
monogamous. Shared paternity increased significantly according to the rate of predation of bree
of shared paternity before the the birds maintained the lowest
• 50.5% of swift parrot nests females, suggesting that rates of shared paternity increased when the adult sex ratio became mo
introduction of the sugar glider,
male-biased – i.e., on mainland Tasmania. observed rate of shared paternity
had shared paternity overall,
it is likely that the consistently
• This rate of shared paternity is unusually high compared and byto92.1–94.9%
most parrot under
species.higher
Although we do
although the birds remained
male-biased
know the extent of adult sexpaternity
shared ratio before the introduction of the paternity.
rates of shared sugar glider, it is likely that th
socially monogamous. Shared
further promotes
consistently male-biased this form
adult sex ratio further promotes this form of mating in swift parrots.
paternity increased significantly
of mating in swift parrots.
• Shared paternity is associated with reduced reproductive success in the species.
• Nests that had shared paternity produced fewer fledglings. This could be a result of interferenceSwift parrot chicks. Image: Dejan Stojanovic
Implications and recommendations
The swift parrot is one of management actions required key mainland breeding sites
Australia’s most imperilled birds to halt swift parrot declines and (but this may be impossible)
and is experiencing ongoing rapid reduce extinction risk are to: • ensure that islands remain
decline. It is listed as one of the • protect breeding and foraging sugar glider–free.
20 Australian birds most at risk habitat in Tasmania
Measures to limit the impact
of extinction in the next 20 years. • protect woodland foraging sites of sugar gliders will reduce
In contrast to other threatened on the mainland, particularly female mortality and increase
species, the swift parrot is well- spotted gum forests in the reproductive rates via higher rates
studied, and the relative contribution New South Wales south coast of monogamy, and are considered
of key threats is also well • investigate measures to reduce an important conservation
understood. The most important impacts from sugar gliders at action for swift parrots.
Cited material
Heinsohn, R., Olah, G., Webb, M., Peakall, R. & Stojanovic, D. 2018 Sex ratio bias and shared paternity reduce individual
fitness and population viability in a critically endangered parrot. Journal of Animal Ecology 88, 502–510.
Further Information
Dejan Stojanovic - dejan.stojanovic@anu.edu.au
Cite this publication as NESP Threatened Species Recovery Hub. 2021. Sex ratio bias in swift parrots due to
sugar glider predation and implications for population viability, Project 2.2.2 Research findings factsheet.
This project is supported through funding from the Australian Government’s National Environmental Science Program.You can also read
