Site context: This is the relative importance of a site in terms of its position in the
landscape, taking into account the connectivity needs of a threatened species. This
includes considerations such as movement patterns of the species, the proximity of the
site in relation to other areas of suitable habitat, and the role of the site in relation to the
overall population or extent of a species
Species stocking rate: This is the usage and/or density of a species at a particular site.
The principle acknowledges that a particular site may have a high value for a particular
threatened species, despite appearing to have poor condition and/or context. It includes
GHD | Report for Main Roads Western Australia - Hill River Offset Property, 61/34834 | 57
considerations such as survey data for a site in regards to a particular species population.
It also includes consideration of the role of the site population in regards to the overall
species population viability.
These three components contribute to the final habitat quality score, however the weighting
given to each component is dependent on the ecological requirements of the impacted species
(DotEE 2014c). When determining the suitability of a proposed offset using the guide, the
minimum requirement is that the quality score of the offset site must at least reach the same
value as the quality score of the impact site (i.e. for Stage 1 of the project).
Start quality input value
Input – 9
Based on the assessment below of the three components that contribute to the final habitat
quality score, a strong weighting was given to all three components. Therefore, the survey area
has been assigned a habitat quality score of 9.
An assessment of the quality of the habitat types available to Carnaby’s Black Cockatoo within
the survey area is provided below.
The survey area provides remnant vegetation and habitat
in excellent condition for Carnaby’s
Black Cockatoo. This habitat of the survey area comprises valuable breeding and foraging
resources for the species.
A detractor to the survey area value is the presence of feral species which also use large
hollows suitable for Carnaby’s Black Cockatoo. This includes the Feral Bee and Laughing
Kookaburra. During the tree plot assessment feral bees were recorded in at least one hollow per
Ten actual breeding events were recorded during the survey, which included visual
observations of female birds exiting large hollows. In addition to the 10 confirmed active
hollows, a further eight were consider highly likely to be currently used based on the size of the
hollow, chew marks present and clipped leaves at the base suggesting nest preparation.
Feeding habitat is presented throughout the survey area and feeding evidence was recorded on
Banksia attenuata twice, Marri, Lambertia multiflora and Hakea neurophylla. The feeding habitat
present in the survey area was dense. The observations made were from visible nuts and cones
discarded on the tracks or visual observation of feeding events. Due to the amount of feeding
habitat available it is likely that area is heavily utilised by the species.
Roosting was recorded once during nocturnal surveys and consisted of at least two individuals
perched in a large Wandoo above a running minor drainage line on the southern boundary on
the survey area along Jurien Road. Due to the numbers observed in the survey area it is likely
multiple roosting sites are present.
58 | GHD | Report for Main Roads Western Australia - Hill River Offset Property, 61/34834
Proximity to known breeding sites and larger areas of foraging vegetation. The survey area
is located within the known breeding range of Carnaby’s Black Cockatoo, and
within a region where the vegetation typically contains suitable foraging habitat. The survey area
lies alongside Coomallo Nature Reserve a known Carnaby’s Cockatoo breeding site
recognised under the IBAs as a site for bird conservation (Dutson et al. 2009). The Coomallo
site is known to support 40 breeding pairs of Carnaby’s Black Cockatoo with the main breeding
location only approximately 6 km from the survey area. Carnaby
’s Black Cockatoos are largely
dependent on an abundance of suitable feeding habitat adjacent to breeding sites to provide the
necessary food for the survival of the chick. While breeding, Carnaby’s Black Cockatoos will
generally forage within a 10
15 km radius of their nesting site.
Therefore, the survey area provides a significant area of suitable high quality foraging habitat
within close proximity to known breeding sites in the region. Additionally, from this preliminary
survey at least 10 known breeding sites were recorded within the survey area.
Proximity to Important Bird Areas Thirteen Bird IBA’s have been identified as significant to Carnaby Bla
ck Cockatoo (Dutson et al 2009)
. The criteria used for the designation of IBAs for Carnaby’s black Cockat
oo are sites
supporting at least 20 breeding pairs, or 1% of the population regularly utilising an area in the
non-breeding part of the range. There are four IBAs within close proximity to the survey area,
Coomallo IBA - known to support at least 40 pairs in nesting and associated feeding
habitat. This IBA is located next to on the eastern boundary of the survey area
The Cataby IBA - known to support at least 24 pairs in nesting and associated feeding
habitat. This IBA is located approximately 55 km south of the survey area
The Moora IBA - known to support up to 60 breeding pairs which nest in woodland
remnants and isolated paddock trees and feed in native shrublands in the town of Moora.
This IBA is located approximately 80 km south-east of the survey area
The Koobabie IBA
known to support up to 32 breeding pairs which nest in woodland
remnants and feed in native shrublands. This IBA is located approximately 110 km east of
Species stocking rate
Numerous observations of
Carnaby’s Black Cockatoos were observed using the habitat within
the survey area for foraging, roosting and breeding during the field survey, in total 89 birds were
It is difficult to determine the specific density and usage of the survey area
by Carnaby’s Black
Cockatoo. Coomallo Nature Reserve to the east of the survey area is 2,078 ha in size and
supports approximately 40 breeding pairs of Carnaby’s Black Cockatoo. This survey area is only
85 ha smaller and in the same area therefore is likely to hold similar numbers. The reporting of
89 birds within the survey area supports this assessment.
There is currently little information known on the home range of Carnaby’s Black Cockatoo,
however the species will generally forage within a 10
15 km radius of its nesting site. Given that
breeding has been recording within Coomallo Nature Reserve, located within 10 km of the
survey area and within the survey area, the habitats present provide foraging habitat within
close proximity these breeding birds. T
herefore, it is highly likely that Carnaby’s Black
Cockatoos would utilise the survey area for foraging during the breeding season.
GHD | Report for Main Roads Western Australia - Hill River Offset Property, 61/34834 | 59
Future area and quality with and without offset
The risk of loss is a percentage figure that describes the chance that the habitat on the
proposed offset site will be completely lost (i.e. no longer hold any value for the protected
matter) over the foreseeable future (either the life of the offset or 20 years, whichever is
shorter). An estimated risk of loss is entered in the guide for both the business as usual (i.e.
without offset) and with offset scenarios. The difference between these figures is the level of
averted loss provided by the proposed offset.
There are a number of factors that could influence the risk of loss of a site, including:
Presence and strength of formal protection mechanisms currently in place on the
proposed site (e.g. zoning, restrictive covenants or state vegetation clearing laws)
Presence of pending development applications, mining leases or other activities on the
proposed offset site that indicate development intent and likelihood
Average risk of loss for similar sites.
Risk of loss (%) without offset
Input – 15%
The value of 15% was assigned as the property prior to Main Roads purchase was privately
owned for agriculture. The exponential population growth of Western Australia in the past
decade has put increasing pressure on Western Australia to increase horticultural production
and with this increase the need for extra land has also increased.
The value of 15% is the standard risk of loss for the Gin Gin region area used by DotEE during
the previous assessment of other offset sites, in the absence of any specific threats to a parcel
of land (Nikki Ward DotE, pers comm. April 2014). Therefore, the value of 15% has been
applied based on previous corespondance with DoTEE.
Future quality without offset (scale 1-10)
Input – 8
The value of 8 was assigned as without the proposed offset the quality of the habitat for
Carnaby’s Black Cockatoo is likely to slightly decrease given the proximity to cleared and
degraded land and the increased likelihood of disturbance, such as weed encroachment and
feral species increases. During the field survey a number of hollows were observed with bees
present, at a rate of approximately one hollow per hectare. There is the potential the rate of
infestation could increase further reducing the number of large hollows available. In addition,
there is the potential for fire to pass from the remnant vegetation surrounding the survey area,
into the survey area which could result in the complete loss of the habitat for Carnaby’s Black
Cockatoo. Without management by DPaW the quality of the habitat is likely to be reduced in the
absence of active management of these issues, i.e. weed, feral bee and fire management.
Risk of loss (%) with offset
Input – 2%
The value of 2% was assigned as the transfer of 564 ha of the total 1993 ha survey area
(including 1771.5 ha of Carnaby’s Black Cockatoo foraging habitat and 560 ha of known
breeding habitat) into conservation estate is unlikely to completely remove all risks to the
proposed offset site, as there will still be a small amount of residual risk the vegetation could be
lost. This risk incorporates rare events, such as a catastrophic wildfire destroying all of the
vegetation within the survey area.
60 | GHD | Report for Main Roads Western Australia - Hill River Offset Property, 61/34834
Future quality with offset (scale 1-10)
Input – 9
The value of 9 was
assigned as with the proposed offset, the quality of the habitat for Carnaby’s
Black Cockatoo is likely to remain the same. The quality of the habitat within the survey area for
Carnaby’s Black Cockatoo is already high, given the excellent site condition,
context for the
species and stocking rate. Therefore, the habitat does not currently require rehabilitation or
revegetation to improve the site condition, and the context and stocking rate are likely to remain
relatively static. The management of the survey area by DPaW will also allow the area to be
actively managed to maintain the viability of Carnaby’s Black Cockatoo habitat.
Confidence in result (%)
The confidence in result is a percentage figure that describes the level of certainty about the
success of the proposed offset. Proposed offset actions that are designed to have a lower risk
of failure should have a higher confidence in result score.
Averted loss component input – 80%
Change in habitat quality component input –
The value of 80% was assigned to the adverted loss component as there is a very high level of
confidence in the strength and effectiveness of the proposed conservation covenant.
For the change in habitat quality component, a value of 80% is assigned as there is a high level
of certainty that management of the survey area by DPaW (including management measures
such as weed control, feral bee control, maintenance of firebreaks and fencing) will maintain
and improve the quality of the Carnaby’s Black Cockatoo habitat.
It should be noted that Main Roads have not currently allocated funds to the future management
or improvement of the proposed offset site (i.e. for land management measures such as feral
bee control, fencing and weed control).
Net present value (adjusted hectares)
The calculation of the net present value is a form of discounting that incorporates the annual
probability of extinction and the relevant time horizons (time over which loss is averted and time
until ecological benefit). It is used to reflect the fact that a given benefit (i.e. improving habitat
quality or averting loss) today holds more value for a protected matter than the same benefit
realised in the future.
Output – 75.63 ha
The outcome meets accounts for greater than 100% (106.57%) direct offset for the impact of
ha of Carnaby’s Black Cockatoo habitat for Stage 1 of the project.
Summary of inputs
A summary of the inputs into the Offsets Calculator for the proposed offset site (the survey area)
is provided in Table 13. The Offsets Calculator is presented in Appendix F.
GHD | Report for Main Roads Western Australia - Hill River Offset Property, 61/34834 | 61
Table 13 Summary of inputs into Offset Calculator
Offset calculator attribute
Proposed offset Portion of Lot 1, 1395 Banovich Road,
Area: 1993 ha including 1771.5 ha
native vegetation and 27.5 ha of highly
Time horizon (years) Time over which loss is averted
Time until ecological benefit
Start area (ha) 564 ha
Start quality (scale of 1-10) 9
Future area and quality with and without offset (%) Risk of loss (%) without offset
Future quality without offset (scale 1-10)
Risk of loss (%) with offset
Future quality with offset (scale 1-10)
Confidence in result (%) Averted loss component input
Change in habitat quality component input
Net present value (adjusted hectares) 75.63
62 | GHD | Report for Main Roads Western Australia - Hill River Offset Property, 61/34834
Vegetation and Flora
Fourteen vegetation types were identified and described from the survey area. The three
woodland vegetation types (VT05, VT09 and VT10) accounted for the majority of the vegetation
within the survey area (69.62%). VT03 and VT07 are associated with Melaleuca species along
drainage lines. The remaining eight native vegetation types are all heathlands with the
vegetation rarely exceeding 150 cm in height and comprised of a range of species at varying
densities in a range of soil types and landforms. As this was not an intensive survey, not all of
the vegetation types may have been accurately assessed or mapped.
Four vegetation types are considered to be conservation significant ecological communities,
VT01 is associated with the Lesueur-Coomallo Floristic Community D1 TEC, listed as
Critically Endangered under the WC Act
VT03 is associated with the Lesueur-Coomallo Floristic Community M2 (Melaleuca preissiana woodland) Priority 1 PEC
VT04 is associated with the Lesueur-Coomallo Floristic Community DFGH Priority 1 PEC,
in particular ‘D’ heath and woodlands on gravelly hills and slopes
VT02 is associated with the Petrophile chrysantha low heath on Lesueur dissected
uplands (Gp200-170) Priority 2 PEC.
All of the native vegetation within the survey area is considered significant vegetation as defined
by the EPA and DPaW (2015). The majority of the survey area is in a Pristine condition that
contains different combinations of taxa associated with a variety of heathlands and provides a
linkage between Lesueur National Park and Coomallo Nature Reserve. In addition, the
vegetation is a refuge for a number of conservation significant flora that occur throughout the
survey area in a variety of vegetation types.
Nine conservation significant flora were recorded from the survey area during the field survey
Hakea megalosperma (listed as Vulnerable under both the EPBC Act and WC Act)
Acaciaretrorsa (Priority 2)
Grevilleadelta (Priority 2)
Thelymitravariegata (Priority 2)
Hensmaniastoniella (Priority 3)
Lepidobolusquadratus (Priority 3)
Stylidium ?hymenocraspedum (Priority 3)
Stylidium ?torticarpum (Priority 3)
Hakeaneurophylla (Priority 4).
The locations and counts of conservation significant flora within the survey area are likely to
increase if the survey effort was to increase to a Level 2 survey during the correct season (mid-
September to October).
The majority of the survey area is in a Pristine condition with the presence of introduced species
generally restricted to the cleared paddock area, along creeklines and the borders of vegetation
GHD | Report for Main Roads Western Australia - Hill River Offset Property, 61/34834 | 63
to previously cleared areas (see Section 4.1.3). Thirteen introduced taxa were recorded within
the survey area during the field survey. The most commonly recorded weed species in the
survey area include *Arctotheca calendula, *Hypochaeris glabra and *Romulea rosea. No
introduced species listed as a Declared Pest plant under Section 22 of the BAM Act or a WoNS
(DotE 2016d), was recorded within the survey area.
Seven main fauna habitat types were recorded during the field survey, which broadly aligned
with the vegetation associations and include, Wandoo Woodlands (560 ha), Marri Woodland
(640 ha), Eucalyptus todtiana, Banksia attenuata/ menziesii low Open Woodland (219 ha),
minor drainage lines and seasonally inundated areas and dams (35 ha), Low Heathlands on
sandy soils (128 ha), Low Heathlands on lateritic soils (164 ha) and scattered trees of Wandoo
and Marri in paddock (248 ha of which 27.5 ha is scattered Wandoo and Marri).
One hundred and seven fauna species were recorded within the survey area during the survey,
these included, 72 birds, 18 mammals (6 introduced), 12 reptiles and five frogs. Off these
species two were identified as conservation significant
and consisted of Carnaby’s Black
Cockatoo listed as endangered under both EPBC and WC Acts and Brush Wallaby listed as
priority 4 under DPAW.
Carnaby’s Black Cockatoo were recorded via observations of birds (89 individuals), actual
breeding events (10 birds recorded in hollows) with an additional 8 records of hollows highly
likely used or being used (but not confirmed), five records of feeding behaviour and one location
The EPBC Act Offsets Assessment Guide has been used to determine the required offsets for
impacts to Carnaby’s Black Cockatoo for Stage 1 of
the Mitchell Freeway Extension.
The outcome based on an offset area of 564 ha accounts for greater than 100% (106.57%)
direct offset for the impact of clearing 88.7 ha of
Carnaby’s Black Cockatoo habitat for Stage 1
of the project.
64 | GHD | Report for Main Roads Western Australia - Hill River Offset Property, 61/34834
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JS Beard (eds) Kwongan - Plant Life of the Sandplain. University of Western Australia
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retrieved May 2016, from http://www.environment.gov.au/cgi-
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