PhD student Annemarie van Doorn has studied one of
northern Australia's endemic bird species—the Purple-crowned
Fairy-wren—along the Victoria River for the past five
Her findings will underpin a new managment plan
for the bird in the Northern Territory, and one that coincides with
good land management practice: controlling erosion and weeds in
The Male Purple-crowned Fairy-wren. Some significant threats
to the wren’s survival were identified by Annemarie’s
study and included weeds, erosion, fire and grazing.
Above, an eroded area along the Victoria River, ripe for invasion
by weeds such as noogoora burr and castor oil plant.
Above, this healthy stand of river grass is needed by the wren and
will also help stablise river banks, which in turn will help
prevent weed incursion and provide habitat for other birds such as
the Yellow-rumped Mannakin
All photos Annemarie van Doorn
The western sub-species of the Purple-crowned Fairy-wren
(Malurus c. coronatus) lives in riverside vegetation in northern
Australia from the Kimberley in Western Australia east to the
Victoria River District in the Northern Territory.
However, its presence is patchy, and it is currently listed as a
vulnerable species. This patchy distribution has been attributed to
both habitat degradation and alteration (Garnett & Crowley
2000, Rowley & Russell 1993).
As the wren is restricted to riparian habitat it is a good
candidate for studying the impacts of some of the primary threats
to biodiversity in northern Australia. There has already been one
previous study, however, in habitat decidedly different from the
one it occupies along the Victoria River (Rowley & Russell
Purple-crowned Fairy-wren habitat
In the Victoria River District the wren occupies river grass
(Chionachne cyathopoda) sometimes in conjunction with
northern cane grass (Mnesithea rottboelioides).
River grass forms dense stands along the Victoria River and its
tributaries and is often referred to as cane grass, however this
term has been used for a multitude of riverine grasses causing some
confusion in the past. The Purple-crowned Fairy-wren depends
heavily on this grass for breeding, foraging and cover; it was not
found in areas without river grass coverage.
Because so many areas along the Victoria River are difficult to
access, in the past the extent of river grass coverage could only
be estimated. However, a helicopter survey conducted during this
study found that river grass does not occur in a continuous stretch
but is highly fragmented consisting of multiple patches of varied
This poses a major problem to the long-term viability of the
wren, as it has limited abilities to disperse. However, the largest
and healthiest patch of river grass occurs within Gregory National
Park where park staff are working to preserve this species and its
Threats to the population
The primary threats to populations of wrens include grazing,
weeds, erosion and fire. These threats are confounding and often
have cumulative effects. In particular, intense grazing at unfenced
sites was identified as the primary threat to the population. The
effects of grazing were most noticeable during the end of the dry
season when cattle tended to congregate along the riparian corridor
and caused significant damage to river grass stands. During
Annemarie’s study where two previously ungrazed sites were
subjected to intense grazing, there was at least a 50% reduction in
the abundance of Purple-crowned Fairy-wrens. This decrease can be
attributed to a lack of cover which ultimately reduced forage and
breeding opportunities as well as increasing predation rates.
Weeds were abundant in the river grass habitat, in particular
Noogoorra burr (Xanthium strumarium) and castor oil plant
(Ricinus communis) were present at all research sites.
Although the Purple-crowned Fairy-wren did forage among these
species, in particular Noogoorra burr, it only did so during the
short period that the plant was green (at the beginning of the dry
season). However, once this species dries it provides no cover or
foraging opportunities and at no time of the year was it an
adequate nesting substrate.
Both these weeds are more prolific in open and disturbed areas
and especially in areas where intense grazing has led to an
increase in the percentage of bare ground.
In addition to weeds, erosion is widespread in the Victoria
River District and has no doubt been exacerbated by the large
floods in recent years. River grass regenerated quickly after
flooding, however once the root base has disappeared
re-colonisation—based on seed propagation
alone—takes much longer.
Only one fire was witnessed during this project which resulted
in low adult mortality, mainly due to the small area affected.
River grass regenerated very quickly after the fire and the area
was re-colonised within one breeding season. For the majority of
the year, river grass does not burn easily but a fire at the end of
the dry season can result in a widespread burn, particularly in an
area of dense river grass with high connectivity such as in Gregory
Conservation of river grass will have widespread positive
outcomes in the Victoria River District in addition to conserving
Purple-crowned Fairy-wrens and providing habitat for other species,
such as the Yellow-rumped Mannakin (Lonchura flaviprymna).
In addition to species-specific effects, river grass can also help
stabilise riverbanks as well as reduce the amount of bare ground
available for weeds to establish.
Greening Australia is currently investigating propagation
techniques for river grass that will further enhance any future
Changing land practices (i.e. fencing and erosion control) in
combination with an increased interest in this species on
properties in the district indicate that there is a possibility of
reducing and possibly reversing some of the threatening processes.
A comprehensive and multi-faceted management plan is being
developed using the findings of this study. This management plan
will provide valuable management options to conserve River Grass
and Purple-crowned Fairy-wren habitat in the Victoria River
Garnett, S.T. & Crowley, G.M. 2000, ‘The Action Plan
for Australian Birds’, Environment Australia, Canberra.
Rowley, I. & Russell, E. 1993, ‘The Purple-crowned
Fairy-wren Malurus coronatus. I. History, distribution and present
status’, Emu, 93:220–234.
This collaborative project was funded by the Victoria River
District Conservation Association, TS–CRC, and the
School for Environmental Research, CDU. Additional assistance by
Gregory National Park and Biodiversity Conservation Unit of NT
Dept. Natural Resources, Environment and The Arts. Research was
conducted in partial fulfilment of the PhD through the University
of Florida (Supervisors: Dr Patricia Werner, Dr John Woinarski and
Dr Barry Brook).