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Subspecies Conservation Summary
Slender-billed Thornbill
(Gulf St Vincent)
Acanthiza iredalei rosinae Mathews, 1913
Acanthizidae
Conservation status
Vulnerable B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)
Reasons for listing
Extent of occurrence is <5000 km2 and birds occupy
<500 km2 but not severely fragmented and risk from
coastal development, with a consequent decline in EOO,
AOO, quality of habitat, and number of locations,
subpopulations and mature individuals, is spread across
at least 10 locations
Status 2000
Vulnerable B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)
Status 1990
Vulnerable B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)
Taxonomy
A. i. hedleyi (south-east South Australia and central
western Victoria) and A. i. iredalei (southern arid zone of
Western Australia and South Australia west to Spencer
Gulf) are Least Concern, as is the species
Taxonomic uniqueness: medium (14 genera/family, 12
species/genus, 3 subspecies/species)
Range
This subspecies is patchily distributed around the northern shores of the Gulf of St Vincent, South Australia
(Higgins and Peter 2002) from St Kilda to Ardrossan
with 3 population foci: Price, Clinton Conservation Park
to Sandy Point and Port Prime south to Torrens I.
(Matthew 1994). The Price and Clinton Conservation
Park regions are assumed to exchange birds occasionally
along the narrow coastal strip as there is a record from
between the 2 at Port Arthur (Matthew 1994). Specimens
were collected at Port Broughton, Spencer Gulf, in 1917,
but there have been no records since (Matthew 1994)
despite searching. This subpopulation is assumed to have
been lost, and may in case have been more closely related
to A. i. iredalei than A. i. rosinae (L. Pedler in litt.). The
bird has also probably disappeared from around Port
Adelaide (Matthew 1994). It is assumed that some of the
loss has occurred within the last 3 generations (37 years),
constituting a small but continuing decline. The AOO is
calculated from the approximate area of suitable habitat
around Gulf St Vincent. Given the number of tenures
within the AOO, there are at least 10 locations, though
many of the smaller ones would not hold viable populations on their own.
Abundance
There are probably about 4300 mature individuals. Based
on densities of about 5.6 birds/ha, and adjusting the esti-
mates of maximum numbers from Matthew (1994) to his
subsequent lower estimate of density (Matthew 2002),
there are likely to be no more than 600 mature individuals at Price, 2200 from Clinton Conservation Park to
Sandy Point, and about 1500 from Port Prime south to
Torrens I. (assuming lower densities than at Clinton Conservation Park; Matthew 1994). Matthew (1994) thought
there might still be 1000 birds on Spencer Gulf but, after
93 years, this assumption is not made here, especially
given the taxonomic uncertainty. The subspecies has also
disappeared from around Port Adelaide (Matthew 1994).
Ecology
Occupies chenopod shrublands, particularly samphire
dominated by Sclerostegia arbuscula, on narrow coastal
saline mudflats, usually within 20 m of a tidal channel or
saline lakes. It also occasionally feeds in Grey Mangrove
Avicennia marina and among other chenopod species
(Mathew 1994, 2002). They build globular nests in low
shrubs, laying 2–4 eggs (Higgins and Peter 2002). Densities of 2.9–8.4 birds/ha have been recorded in suitable
habitat at Clinton Conservation Park, but are thought to
be lower in the southern subpopulation (Matthew 1994).
A generation time of 12.3 years (BirdLife International
2011) is derived from an age at first breeding of 1.0 years
(extrapolated from congeners) and a maximum longevity
of 23.5 years (extrapolated from Striated Thornbill
A. striatus, Australian Bird and Bat Banding Scheme).
Threats
This subspecies has suffered from habitat loss, particularly cumulative minor developments in the southern
part of its range (Grady and Brook 2002), though its disappearance from Port Broughton is unexplained. Though
generally unattractive for rural or residential development, the fringes of some salt-flats have been reclaimed
for recreational and industrial use, such as for salt works.
Other coastal residential and commercial developments,
such as marinas, are proposed in parts of the subspecies’
range. Inappropriate water management and use also
© Birds Australia 2011
Published by CSIRO Publishing, http://www.publish.csiro.au/
Citation: Garnett ST, Szabo JK, Dutson G (2011) The Action Plan for Australian Birds 2010. CSIRO Publishing, Melbourne.
Current eligibility against IUCN Red List Criteria
IUCN
category
A
Criteria eligibility
Not applicable: past, current or future population
declines are thought unlikely to exceed 20% in any
3-generation period
B
Vulnerable: EOO <20 000 km2, AOO <2000 km2,
population at ≤10 locations, inferred continuing decline
in EOO, AOO, area, extent and quality of habitat, no.
locations, no. subpopulations, no. mature individuals
C
Not applicable: population 2500–10 000 mature
individuals, continuing decline not observed or
estimated, largest subpopulation >1000 mature
individuals, >1 subpopulation
D
Not applicable: population >1000 mature individuals,
>5 locations
E
Not applicable: no population viability analysis
undertaken
IUCN Red List assessment data
Estimate
Reliability
Extent of occurrence
trend
1600 km2
decreasing
high
medium
Area of occupancy
trend
60 km2
decreasing
medium
medium
No. of mature individuals
trend
4300
decreasing
low
medium
No. subpopulations
2
medium
No. locations
10
medium
2200
low
Largest subpopulation
Generation time
Global population share
12.3 years
low
100%
high
threaten their habitat. Other threats include recreational
activities and site disturbance, grazing and disturbance
by rabbits Oryctolagus cuniculus and predation by foxes
Vulpes vulpes and feral and uncontrolled cats Felis catus
(Willson and Bignall 2009).
Grady M, Brook J (2000) ‘Submission by The Conservation
Council of South Australia Inc. to the Senate Inquiry into
Gulf St Vincent’. The Conservation Council of South Australia Inc., Adelaide. Retrieved 10 May, 2011 from <http://
www.ccsa.asn.au/submissions/gulfstvincent.htm>.
Conservation objectives
1. Existing subpopulations retained and viable
Higgins PJ, Peter JM (Eds) (2002) Handbook of Australian, New
Zealand and Antarctic Birds. Volume 6: Pardalotes to Spangled Drongo. Oxford University Press, Melbourne.
Information required
1. Population trends, particularly near developed areas
2. Impacts of proposed threats
3. Extent of movement between subpopulations/regions
Management actions required
1. Establish annual monitoring sites, particularly at
fringes of range
2. Determine genetic connectivity between
subpopulations/regions
3. Work with local government and the Coast
Protection Board to secure all remaining habitat
Bibliography
Matthew J (1994) The status, distribution and habitat of the
Slender-billed Thornbill Acanthiza iredalei in South Australia. South Australian Ornithologist 32, 1–23.
Matthew JS (2002) Notes on the ecology of the Slender-Billed
Thornbill Acanthiza iredalei rosinae. South Australian Ornithologist 34, 15–22.
Willson A, Bignall J (2009) ‘Regional recovery plan for threatened species and ecological communities of Adelaide and
the Mount Lofty Ranges, South Australia’. Department for
Environment and Heritage, South Australia.
Comments received from
Graham Carpenter, Jamie Matthew, Lynn Pedler
BirdLife International (2011) ‘Species factsheet: Acanthiza iredalei’. Retrieved 17 January, 2011 from <http://www.birdlife.org/>.
© Birds Australia 2011
Published by CSIRO Publishing, http://www.publish.csiro.au/
Citation: Garnett ST, Szabo JK, Dutson G (2011) The Action Plan for Australian Birds 2010. CSIRO Publishing, Melbourne.