Quoll populations reveal grim news as cane toads
Northern Quoll at the Mary River
study site, February 2002.
This Quoll population is now
Photo: Katrina Reid
rabbit-sized marsupial carnivores,
found only in Australia and New
Guinea. There are four Australian
species, and two species restricted
to New Guinea. All Australian
species have declined considerably,
and three (the eastern Quoll D.
viverrinus, the Western Quoll
D. geoffroii and the
spotted-tailed Quoll D. maculatus)
are listed as nationally threatened
Northern Quoll is the smallest of
Quolls, with a maximum weight of 1.2
kg. It shelters during the day in
rock crevices, tree hollows, logs or
termite mounds and forages at night,
both in trees and on the ground, for
invertebrates, vertebrates and
fruit. Northern Quolls have an
annual highly synchronised mating
season; shortly after mating, all
the males in the population die off.
Home range sizes vary from 35 ha (in
females) to over 1 km2
for males in savanna woodland.
Woinarski & Meri Oakwood
As their range
has expanded into the Northern Territory, there
has been considerable debate over what impact
cane toads will have on the native fauna (See:
‘The cane toad dialogues: disaster or
disruption’, Savanna Links, 16, p. 1).
Some experts, such as Professor Mike Tyler
from the University of Adelaide, forecast an
ecological disaster affecting a range of
Other scientists, such as Dr Bill Freeland,
former head of the NT Parks and Wildlife
Commission, believe that although species may
suffer massive declines initially, they will
bounce back within a few seasons. Unfortunately,
in the areas of Queensland that experienced toad
invasion years ago, no methodical scientific
monitoring was conducted. We only have a couple
of field studies in the Gulf
country 1, 2 and anecdotal stories
from Queensland on which to base predictions.
Click on thumbnail to enlarge
View with Quoll
den in foreground, Mary
River district, Northern
frequently den in rocky
boulder piles, often at
the highest points of
hills or outliers.
toads reached Kakadu in 2001, and were first
recorded in the south-east at the junction of
Gimbat Creek and a creek from Mt Evelyn in April
of that year. Since then they have spread
northwards and westwards across the Park with
sightings now occurring in Jabiru.
There have been several projects instigated in
the Park to monitor the effect of cane toads on
the native fauna. Professor Gordon Grigg
(University of Qld), Dr Andrew Taylor (UNSW) and
Hamish McCallum (UQ) installed audio monitors at
six sites to determine whether the composition
of the native frog community changes. Dr Dan
Holland has radio-tracked the two largest
species of woodland goannas, Varanus panoptes
and V. gouldii. Michelle Watson (Charles
Darwin University) has been conducting
broad-scale fauna surveys before and after toad
invasion. I have been monitoring two populations
of northern Quolls, Dasyurus hallucatus,
considered to be a high-risk species of
Profile of the Northern Quoll
Northern Quolls are opportunistic predators,
consuming anything that moves that is within a
size range that they can manage. They eat
several species of native frogs 3 and
cane toads are easy prey. Unfortunately, all
the Quoll has to do is mouth the toad to cause
it to exude poison from its parotoid glands (the
swellings on each shoulder behind the eardrum).
The poison is then ingested by the Quoll. An
individual of a closely related species of Quoll
was observed mouthing a toad and dying ten
minutes later 4. Some social native
species, such as crows, have been reported to be
able to consume toads safely by turning them
over and only devouring the stomach region.
Unfortunately, northern Quolls are solitary
hunters 5, so there is little chance
that they will learn safe toad-consuming
behaviour by observation of other individuals.
Quoll/cane toad project has two study sites: one
in southern Kakadu (Mary River District) and one
in northern Kakadu (East Alligator District)
6. Trapping, radio-tracking and
post-mortem examinations are being used to
monitor the Quolls and road surveys are
conducted to monitor the progress of the toads.
The cane toads reached the Mary River
District in December 2001 and were first
recorded at the study site in February 2002.
Immediately some of the radio-tracked Quolls
were found dead of apparent toad-poisoning.
However, the wet season is normally a time of
high Quoll abundance and high mortality as the
juveniles become independent and compete for the
limited number of territories, so these deaths
had little impact on the population as a whole.
dry season arrived, the toads became less
obvious as they retreated to shelter sites near
water and the Quoll population followed the
usual pattern of slight decline as the dry
season progressed. The mating season was
normal, all of the females had pouch young and
by October, the young were kept in nursery dens.
In October the population was similar to that
of the previous year, at its lowest abundance
for the year. But then the rains began, the
toads began dispersing again and it appears that
as mothers died from poisoning, whole litters of
young starved to death. By December, the
population had crashed with only three
individuals detected during trapping. In
January 2003, there were still only three. In
March, there were none. No Quolls were caught
in May and July. Toads are still increasing
toads the cause?
can we be sure that this sudden decline is due
to toads? To begin with, Quolls that appeared
to have been poisoned by toads began dying the
same month and in the same area that toads were
first observed at the site. These individual
Quolls had been monitored intensively, being
trapped every two weeks, and they were healthy
with no disease and no heavy parasite
infestations. At death, they had no signs of
predator damage or accidental injury, the only
unusual sign being red irritation on the lips in
some animals. There were no obvious changes
in the habitat at the time except for the
arrival of the toads. The most compelling
evidence is that the toad-free East Alligator
area still has a super-abundant Quoll
Quolls at East Alligator are currently being
intensively monitored in preparation for the
cane toad invasion, which may occur this coming
wet season. We expect that the pattern of
decline will probably be similar. This is
very sad as East Alligator has the highest
density of Quolls that I have ever observed in
12 years of working on this species.
massive decline of Quolls to the point of local
extinction was also observed in Michelle
Watson’s study in Kakadu which found that Quolls
were not recorded at all in quadrats invaded by
toads, though they had been present the year
before7. So, it certainly appears
that in the short-term at least, the arrival of
the toads has been disastrous for the northern
Quoll. Quolls were already declining
throughout the Top End and the toad has
certainly hastened the process. So, will
numbers bounce back as predicted by Dr Freeland?
Only time will tell.
will re-trap at Mary River at least once more
this year, and hope to continue to monitor the
site (and East Alligator) throughout 2004.
The only way to address the question of
long-term impact, is to conduct methodical
long-term monitoring, so hopefully we will be
able to revisit these sites at least once a year
until about 2010.
1. Freeland, WJ, & Kerin, S H 1988,
‘Within-habitat relationships between invading
Bufo marinus and Australian species of
frog during the tropical dry season’,
Australian Wildlife Research 15, 293–305.
2. Catling, PC, Hertog, A, Burt, RJ, Wombey, JC,
& Forrester, R ‘The short-term effect of cane
toads (Bufo marinus) on native fauna in
the Gulf Country of the Northern Territory’,
Wildlife Research 26, 161–185.
3. Oakwood, M 1997, The ecology of the Northern
Quoll, Dasyurus hallucatus, PhD thesis,
Australian National University.
4. Prof. M Archer, Director of the Australian
Museum, pers. comm.
5. Oakwood, M, ‘Spatial and social organisation
of a carnivorous marsupial, Dasyurus
hallucatus (Marsupialia: Dasyuridae)’,
Journal of Zoology, London 257, 237–248.
6. Oakwood, M 2003, ‘The effect of cane toads on
a marsupial carnivore, the northern Quoll,
Dasyurus hallucatus’, Report to Parks
7. Watson, M., and Woinarski, J. 2003.
Vertebrate monitoring and re-sampling in Kakadu
National Park, 2002. Report to Parks Australia
This article has
been reproduced with the kind permission of Dr
Meri Oakwood and Savanna Links Newsletter.
Dr Meri Oakwood
Envirotek Research, Survey and Education
Phone: 02 6656 9079