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The Growling Grass Frog and the Late-
Spring and Summer Breeding Frogs of
North-Western Victoria
Status, Distribution, and Habitat Requirements in the Kerang and
Mildura regions
Michael J. Smith, Michael P. Scroggie, and Ruth Lennie
2008
Arthur Rylah Institute for Environmental Research
Technical Report Series No. 171

Arthur Rylah Institute for Environmental Research Technical Report Series No. 171
The Growling Grass Frog and the Late-
Spring and Summer Breeding Frogs of
North-Western Victoria
Status, Distribution, and Habitat Requirements in the Kerang and
Mildura regions
Michael J. Smith, Michael P. Scroggie, and Ruth Lennie
Arthur Rylah Institute for Environmental Research
123 Brown Street, Heidelberg, Victoria 3084
February 2008
Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment.
Heidelberg, Victoria.

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Citation
Smith, M. J., Scroggie, M. P., and Lennie, R. (2008) The Growling Grass Frog and the Late-Spring and Summer
Breeding Frogs of North-Western Victoria: Status, Distribution, and Habitat Requirements in the Kerang and
Mildura regions. Arthur Rylah Institute for Environmental Research Technical Report Series No. 171.
Department of Sustainability and Environment, Heidelberg, Victoria.
ISBN (print) 978-1-74208-260-8
ISBN (online) 978-1-74208-261-5
ISSN (print) 1835 3827
ISSN (online) 1835 3835
Disclaimer
This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that
the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore
disclaims all liability for any error, loss or other consequence which may arise from you relying on any
information in this publication.
Front cover photo: Growling Grass Frog Litoria raniformis (Michael Smith). All other photographs taken by
Michael Smith
Authorised by the Victorian Government, Melbourne.
Printed by: NMIT Printroom, 77-91 St Georges Road, Preston 3072

Contents
List of tables and figures .........................................................................................................................ii
Acknowledgements ................................................................................................................................ iii
Summary................................................................................................................................................... iv
1 Introduction.......................................................................................................................................1
1.1 Objectives............................................................................................................................................... 3
2 Methods ..............................................................................................................................................4
2.1 General Design ............................................................................................................................... 4
2.2 Statistical Analyses........................................................................................................................ 6
3 Results ................................................................................................................................................7
3.1 Occupancy and Detectability ...................................................................................................... 7
3.2 Habitat Requirements................................................................................................................. 15
4 Discussion....................................................................................................................................... 19
4.1 Recommendations.............................................................................................................. 21
5 References....................................................................................................................................... 23
6 Appendix 1. Sample data sheet................................................................................................... 25
i

List of tables and figures
Table 1: General description and conservation status of species expected to breed in the
study regions from late spring and summer. Conservation status for secure species is
based upon a classification by the Department of Sustainability and Environment
(Department of Sustainability and Environment 2003)................................................................3
Table 2: The number of sites in each water body category that frog species were detected in.
.......................................................................................................................................................................7
Figure 1: Map showing the historical records for the Growling Grass Frog in Victoria and the
two study areas, Kerang region (right) and the Mildura region (left).......................................2
Figure 2: Distribution of study sites in the Kerang and Mildura regions. Sites where both
physical and chemical measurements were made are indicated. Axes markers are UTM. 5
Figure 3: Location of study sites in the Kerang and Mildura regions, including those where
the Growling Grass Frog was detected. Axes are in UTM. ...........................................................8
Figure 4: Location of study sites in the Kerang and Mildura regions, including those where
Peron’s Tree Frogs were detected. Axes are in UTM......................................................................9
Figure 5: Location of study sites in the Kerang and Mildura regions, including those where
the Barking Marsh Frog was detected. Axes are in UTM. ...........................................................10
Figure 6: Location of study sites in the Kerang and Mildura regions, including those where
the Spotted Marsh Frog was detected. Axes are in UTM...........................................................11
Figure 7: Location of study sites in the Kerang region, including those where Pobblebonk
Frogs (Top) and the Common Froglet (Bottom) were detected. Axes are in UTM. .............12
Figure 8: Location of study sites in the Kerang and Mildura regions, including those where
the Plains Froglet was detected. Axes are in UTM........................................................................13
Figure 9: Estimates of detection probability and occupancy for each species conditional on
covariate values. Solid circle represents median occupancy or detectability and lines
indicate 95% credible intervals...........................................................................................................14
Figure 10: Posterior means (solid circle) and their 95% credible intervals of the model
parameters explaining the relationship between expected occupancy of each species
and region (Kerang or Mildura), percentage aquatic vegetation cover, and conductivity.
A vertical line has been included to show distributions relative to zero. ............................15
Figure 11: Changes in expected occupancy of the Growling Grass Frog (top) and the Barking
Marsh Frog (bottom) with percentage aquatic vegetation cover. Conductivity was held
constant at a mean value. Solid line indicates posterior median and dashed lines 95%
credible intervals....................................................................................................................................16
Figure 12: Changes in expected occupancy of each species with wetland conductivity, while
holding percentage aquatic vegetation at a mean value. Solid line indicates posterior
median and dashed lines 95% credible intervals. Dashed red vertical lines indicate 8%
seawater. ...................................................................................................................................................17
Figure 13: Changes in predicted species number with wetland conductivity, while holding
percentage aquatic vegetation at a mean level. The solid line indicates the posterior
median expected number of species. Dashed lines are 95% credible intervals on the
inferred relationship. Dashed red vertical line indicates 8% seawater. .................................18
ii

Acknowledgements
This project was funded by the National Heritage Trust and the Department of Sustainability
and Environment, Biodiversity Group North West Region. We especially thank Peter Johnson,
Derek Turnbull, Keely Ough, Michele Kohout, Shar Ramamurthy and Nick Clemann for their
contributions to the project.
iii

Summary
An intensive survey of amphibians in the Kerang and Mildura regions during late spring and
summer of 2006/2007 resulted in the detection of seven species. The distribution of the
focal species, the Growling Grass Frog, varied amongst regions. In the Kerang area, we only
detected the species in irrigation channels and farm dams. In the Mildura area, the Growling
Grass Frog was only detected in wetlands that had received environmental flows , located
within the Mulcra Island State Forrest. In contrast to the other frog species, the Growling
Grass Frog had a low rate of occupancy, and occupied sites tended to be close to each other,
indicating a restricted, clustered distribution within the study regions. This observation is
important from a management perspective as it suggests that habitat creation, conservation,
and/or restoration should focus on areas where the frogs are known to occur and perhaps
be designed to make habitat links between known sites where possible.
We surveyed sites on a maximum of three occasions each, and found varying detection
probabilities among the species encountered. Due to imperfect probabilities of detection,
effective monitoring of even the most detectable species will require repeated surveys
during appropriate times to assign likelihoods of presence when the species is not detected,
and to provide valid inferences regarding the relationships between habitat attributes and
probability of occupancy.
Occurrences of the Growling Grass Frog and the Barking Marsh Frog were positively
associated with the extent of aquatic vegetation (emergent and/or submerged).
Supplementation of aquatic vegetation may be an effective management action for habitat
restoration and enhancement for these species. For each individual species and for the
overall number of species present, we found a low likelihood of occupancy when water
conductivities were greater than 4000 EC (equivalent to approximately 8% seawater). We did
not detect a strong relationship between salinity and occupancy for the Growling Grass
Frog, probably due to high uncertainties associated with the low occupancy rate of this
species and spatially restricted distributions. Collection of further distribution data will
reduce uncertainty regarding the salinity tolerance of this species, and provide better
resolution for that relationship. However, we would expect that the salinity tolerance of this
species would not be much higher than that of the other frog species considered in the
study.
The frog species present in the study regions made use of a variety of freshwater habitats
ranging from still sections of creeks through to farm dams. In the Kerang region, irrigation
channels were commonly utilised, highlighting the potential importance of these water
bodies as refuge habitat during times of drought. We encourage continued efforts to engage
community support and training for frog conservation efforts in the region, as much of the
extant amphibian diversity and habitat in the study regions occurs on private property, and
will require the cooperation of landholders. Adaptive management of habitat, as part of an
experimental program of habitat alteration and enhancement may provide a mechanism for
managing habitats for the persistence of frog populations, whilst providing necessary
information to ensure that management activities are of maximal effectiveness.
.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
1 Introduction
The frog fauna of Victoria vary considerably in their conservation status, ranging
from widespread, secure species (e.g., Common Froglet Crinia signifera) through to
geographically restricted, critically endangered taxa ( e.g., Spotted Tree Frog Litoria
spenceri, Department of Sustainability and Environment 2003). Knowledge gaps exist
for even well-studied species, and typically we have limited understanding of the
current distribution and abundance of most frog species within the state. It is
reasonable to expect that populations will experience a range of demographic
responses to environmental stimuli that include both natural events (e.g., drought)
and human-induced threats like climate change, introduced pathogens, habitat
modification, and introduced predators (Alford and Richards 1999). Monitoring of
the frog fauna, allows declining populations to be detected and persisting or
recolonising populations to be identified.
There are a number of threatening processes currently acting upon Victoria’s frog
fauna, including climate change, drought, introduced pathogens, and habitat
modification (e.g., Alford and Richards 1999). Drier climates are predicted for parts
of Victoria (National Resource Management Ministerial Council 2004) which, together
with various forms of habitat modification and degradation, may pose a threat to the
persistence of components of the frog fauna in many areas. Processes like secondary
salinisation lead to degradation of habitat (Smith et al. 2007), and additional natural
and anthropogenic processes, like drought and wetland draining, can place further
stresses upon remaining habitat (e.g., Beebee and Griffiths 2005). In many of
Victoria’s modified environments, large areas of freshwater habitat are available in
irrigation channels and farm dams and these waterways may be an important source
of fresh surface water during periods of drought. Understanding how the frog fauna
utilises a range of different habitat types and assessing their response to various
habitat gradients (e.g., changes in water chemistry and vegetation) will be critical for
management of habitat.
The concept of the “best 50% of habitat” has emerged as a process for determining
the conservation significance of habitat for Victoria’s flora and fauna (Department of
Natural Resources and Environment 2002; Department of Sustainability and
Environment 2007). There are a number of difficulties in applying this concept to
amphibians, foremost being a limited capacity to determine two important criteria;
relevant vegetation condition with respect to the target species and the average
vegetation condition of each Ecological Vegetation Class (EVC). The Department of
Sustainability and Environment is developing a condition assessment map, but this
will have limited applicability for most amphibian species as non-native vegetation is
given a condition score of zero; many amphibians readily utilise highly modified
habitats in rural settings. Further, applying the best 50% habitat concept requires an
understanding of the metapopulation structure of the target species at local and
regional scales and an ability to discriminate between the importance of different
populations. These data are rarely available for frogs. Finally, frogs are almost
always surveyed during their breeding phase and consequently, there is virtually no
knowledge of their habitat requirements during non-breeding phases. We therefore
are not in a position to apply the best 50% habitat concept in its current form to
frogs species in the study area. However, we do make note of the bioregions and
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
EVCs that the focal species of this study, the Growling Grass Frog, was detected in
for future reference.
The study is centred on the Kerang and Mildura regions (Figure 1) and focuses on
the late spring-summer breeding and threatened Growling Grass Frog (Litoria
raniformis). We also opportunistically surveyed for other late spring-summer
breeding frog species (Table 1).
The Growling Grass Frog is a member of the Bell Frog species group (Thomson et al.
1996) that historically, was known to occur throughout substantial areas of south
eastern Australia. In Victoria the species was formerly widespread and common
(Figure 1), but in recent decades range contractions have been observed (Clemann
and Gillespie In prep.). The Growling Grass Frog is often associated with aquatic
habitats that feature large areas of vegetation within and around the water body. The
Growling Grass Frog is usually associated with still or slow flowing water bodies and
has the capacity to inhabit disturbed areas that include artificial water bodies (e.g.,
farm dams and irrigation channels). Larval period can vary dramatically, from as
short as a few months to as long as fifteen months. With the exception of the
Barking Marsh Frog (Limnodynastes fletcheri), the other species that are thought to
breed in the area during the survey period are not currently of conservation concern
(Table 1).
Figure 1: Map showing the historical records for the Growling Grass Frog in
Victoria and the two study areas, Kerang region (right) and the Mildura region
(left).
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
1.1 Objectives
The main objective of this study was to provide the Department of Sustainability and
Environment Biodiversity Group North West Region with distribution and habitat
information for the Threatened Growling Grass Frog and for other late-spring and
summer breeding species that are known to occur (or are likely to occur) within the
Kerang and Mildura regions (Table 1). The study aimed to improve our
understanding of habitat requirements for these species and to develop sampling
protocols for more future frog surveys in the region.
Table 1: General description and conservation status of species expected to breed
in the study regions from late spring and summer. Conservation status for secure
species is based upon a classification by the Department of Sustainability and
Environment (Department of Sustainability and Environment 2003).
Common name Species Family Conservation
status
Common Froglet Crinia signifera Myobatrachidae secure
Plains Froglet Crinia parinsignifera Myobatrachidae Secure
Barking Marsh Frog Limnodynastes fletcheri Myobatrachidae Data deficient
Pobblebonk Limnodynastes dumerilii Myobatrachidae Secure
Spotted Marsh Frog Limnodynates
tasmaniensis
Myobatrachidae Secure
Common Spadefoot Neobatrachus sudelli Myobatrachidae Secure
Toad
Peron’s Tree Frog Litoria peronii Hylidae Secure
Growling Grass Frog Litoria raniformis Hylidae Endangered
(EPBC:Vulnerab
le and listed in
FFG)
Peron’s Tree Frog (Litoria peronii)
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
2 Methods
2.1 General Design
The study was conducted in the Kerang and Mildura regions of Victoria (Figure 2) in
areas where the Growling Grass Frog has been recorded. In the Kerang region, roads
within the historical distribution of the Growling Grass Frog were haphazardly
selected and driven during the day. Groups of potential sites (wetlands, dams, lakes,
and still sections of streams and irrigation channels) were identified and their
locations recorded with a Global Positioning System (GPS) receiver. The sites were
then surveyed for the presence of frogs at night. Heard et al. (2006) found that
multiple night-time surveys were necessary to ensure an adequate probability of
detection for adults of the Growling Grass Frog, and accordingly, we conducted
repeated nocturnal surveys for frog calls. Sites were surveyed in October, November
and December. Some sites were not sampled on all three occasions (mean number of
surveys = 2) due to factors like drying of some water bodies. A similar sampling
process was followed in the Mildura region, but the sites were sampled twice each
and the entire sampling was completed within one week in December 2006. We
surveyed 61 sites in Kerang and 16 in Mildura. In the Kerang region, we also
opportunistically surveyed a further 50 sites (hereafter referred to as extra sites), but
no chemical or physical measures of habitat were made at these sites (see below) due
to access difficulties.
At each site, for each survey, we listened for 10 minutes (cf. Scott and Woodward
1994) and documented all calling frog species. In most of the study sites (n = 77), we
measured water conductivity (EC: μS/cm@25°C) using a TPS 90FL multi-parameter
meter. Electrical conductivity was used as a proxy for salinity, and measurements
were made within 15 cm of the water surface. This is an important measure, as
secondary salinisation is an on-going issue in both regions (Walker and Salt 2006),
and high salinities are known to be detrimental to many frog species (Smith et al.
2007). At most sites (n = 61) we estimated the extent of aquatic vegetation (emergent
and submerged) by approximating the proportion of the water body that contained
aquatic plants, which are considered to be important habitat feature for the Growling
Grass Frog and for other species (Heard pers. com). Where the site was linear in
nature (e.g., a section of a stream or irrigation channel), we estimated the extent of
aquatic vegetation along a 100 metre section centred on the survey point. A sample
data sheet is included in Appendix 1.
The Barking Marsh Frog (Limnodynastes fletcheri).
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 2: Distribution of study sites in the Kerang and Mildura regions. Sites
where both physical and chemical measurements were made are indicated. Axes
markers are UTM.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
2.2 Statistical Analyses
As it could not be assumed that each species actually present at a site would
definitely be detected on each visit, it was necessary to account for imperfect
detectability in the statistical analysis of the data. We used the approach to
estimation of occupancy rates under imperfect detection devised by MacKenzie et al.
(2006). In simple terms, this approach treats the sites under consideration as being
drawn from two discrete categories: occupied sites, where on each visit the species
will be detected with an unknown probability, p, and unoccupied sites where the
species will not be detected as it is absent. By carrying out repeated surveys at some
or all sample of sites, it is possible to make statistical inferences regarding the actual
rate of occupancy, allowing for the fact that the species in question may not have
been detected at some sites which are actually occupied. The full statistical theory of
this methodology is beyond the scope of this report – details of the motivation and
derivation of the methods can be found in MacKenzie et al. (2006). In simple terms it
can be appreciated that if detection of the species at a single survey was certain,
then over the course of a set of repeated surveys, sites would either always record
detections (in the case of occupied sites) or always record absences (unoccupied
sites). However, if the probability of detection is less than one, then it would be
expected that a mixture of detections and non-detections would be recorded during
the course of a set of surveys at an occupied site. Using Bayesian statistical
techniques, it is possible to use a statistical model for the processes of occupancy
and detection to make inferences from repeated survey data regarding the
underlying rate of occupancy, as well as the probability of detection at occupied
sites.
The basic form of the occupancy model, where all sites have a common probability
of occupancy, and all surveys have a common probability of detecting the species at
occupied sites, can be readily extended to allow for the effects of covariates on either
the occupancy or detection probabilities associated with sites and surveys. This is
typically done through the use of logistic regression equations within the statistical
model, which relate the probabilities of occupancy or detection to the covariates
values. In the present case, we related the probabilities of occupancy of the various
frog species to habitat variables measured at the sites, including conductivity and
cover of aquatic vegetation. We included up to three predictor terms in each model
as the moderate number of sites (77) from which we sampled, precluded the fitting
of more complex models to the data (see Burnham and Anderson 2002).
We used Bayesian Markov Chain Monte Carlo (MCMC) statistical techniques to fit the
models to the data using the freely-available Bayesian statistics package OpenBugs
2.2.0 (Thomas et al. 2006). Use of a Bayesian formulation of the model had several
advantages in this case; in particular, it was possible to consistently deal with
missing covariate values from several sites, by inferring these values from the data
as a part of the estimation procedure. In addition, Bayesian methods allowed the
straightforward generation of model predictions and related parameters with correct
propagation of uncertainty in the model parameters (see below for further details).
Vague (uninformative) priors were used for all model parameters, including missing
predictor values, leading to inferences that would be expected to match the results
which would be obtained using conventional maximum likelihood inferences. The
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
covariates were centred on their means prior to analysis to aid convergence of the
algorithm used to fit the model to the data. Convergence of the MCMC algorithm was
checked by examining the output of three replicate Markov chains with differing
starting values, both by visual inspection of the outputs and by computing the
Brooks-Gelman-Rubin convergence statistic (Brooks and Gelman 1998). Convergence
was rapid and final inferences were made by discarding the first 10000 iterations
from a single chain and retaining the next 90000 iterations for further inference.
Inferences regarding derived quantities, which are functions of model parameters,
were readily estimated from the data by generating large samples from their
sampling distributions using MCMC methods. This technique allowed us to correctly
propagate uncertainty in the model’s parameters into our inferences regarding the
derived quantities. Using this approach, we inferred the probabilities of individual
species occupancy and the likely total number of species that would be expected to
occur under representative sets of covariate values for each important predictor
variable (cf. Smith et al. 2007).
3 Results
3.1 Occupancy and Detectability
A range of different water bodies were surveyed that included still or slow moving
sections of streams (n=17), natural but modified wetlands (n=6), large lakes (n=10),
irrigation channels (n=31), farm dams (n=2) and ox-bow lakes (n=11). Interestingly,
no frog species were actually heard calling in the Murray River, but instead they were
utilising habitats near to the River, such as oxbow lakes, irrigation channels and
smaller creeks and streams. We detected seven species during the study (Figures 3
to 8), whose rates of occupancy and probabilities of detection varied considerably
(Figure 9). With the exception of the Growling Grass Frog, all species were commonly
detected in all water body types which were surveyed (Table 2). We did not detect
the Growling Grass Frog in lake and stream habitats.
Table 2: The number of sites in each water body category that frog species were
detected in.
Species Dam Irrig. Chan. Lake Ox. Lake Stream Wet. Total
Growling Grass Frog 1 11 0 5 0 0 17
Peron’s Tree Frog 0 10 5 7 8 4 34
Common Froglet 0 9 5 11 6 5 36
Plains Froglet 1 20 1 7 6 3 38
Barking Marsh Frog 1 18 5 6 8 5 43
Spotted Marsh Frog 1 19 3 4 3 4 34
Not only was the Growling Grass Frog not detected in many sites (≈40%; Figure 9),
but the sites where they were detected tended to be geographically close to each
other (Figure 3). We did not detect Pobblebonks at any of the main study sites and in
only three of the extra sites. The study period probably did not encompass optimal
breeding conditions for this species, and accordingly we removed this species from
further analyses. The other five species were quite common and widely detected
throughout the study region when compared to the Growling Grass Frog.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 3: Location of study sites in the Kerang and Mildura regions, including
those where the Growling Grass Frog was detected. Axes are in UTM.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 4: Location of study sites in the Kerang and Mildura regions, including
those where Peron’s Tree Frogs were detected. Axes are in UTM.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 5: Location of study sites in the Kerang and Mildura regions, including
those where the Barking Marsh Frog was detected. Axes are in UTM.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 6: Location of study sites in the Kerang and Mildura regions, including
those where the Spotted Marsh Frog was detected. Axes are in UTM.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 7: Location of study sites in the Kerang region, including those where
Pobblebonk Frogs (Top) and the Common Froglet (Bottom) were detected. Axes
are in UTM.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 8: Location of study sites in the Kerang and Mildura regions, including
those where the Plains Froglet was detected. Axes are in UTM.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 9: Estimates of detection probability and occupancy for each species
conditional on covariate values. Solid circle represents median occupancy or
detectability and lines indicate 95% credible intervals.
The Common Froglet (Crinia signifera).
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
3.2 Habitat Requirements
The Growling Grass Frog was recorded in two bioregions, Murray Scroll Belt (Kerang)
and Murray Fans (Mildura). In the Kerang region, the populations were all found
within habitat classified as EVC 99; Non Vegetation. This is an EVC that does not fit
into any recognised category of native vegetation. Accordingly, Victoria’s Native
Vegetation Management Framework, and other related conservation plans (e.g.,
Department of Natural Resources and Environment 2002; Department of
Sustainability and Environment 2007) and proscriptions do not apply to these
habitats. However, these habitats appear to be critically important for the
persistence of the Growling Grass Frog in the study region.
In the Mildura region the Growling Grass Frog populations were detected in
Intermittent Swampy Habitat (EVC: 813), Lignum Shrubland (EVC: 808), Lignum
Swampy Woodland (EVC: 823), Lignum Swamp (EVC: 104) and Shrubby Riverine
Woodland (EVC: 818). Only the Lignum Swamp is considered to be Vulnerable, while
Intermittent Swampy Habitat and Lignum Swampy Woodland are classified as
Depleted.
Occupancy by the Growling Grass Frog and the Barking Marsh Frog were both
positively correlated with the percentage aquatic vegetation cover (Figure 10). Both
these species were more likely to be present in habitat with higher levels of aquatic
plant cover (Figure 11). With the exception of the Common Froglet, all other species
had a positive, albeit weak, relationship with aquatic vegetation.
Figure 10: Posterior means (solid circle) and their 95% credible intervals of the
model parameters explaining the relationship between expected occupancy of
each species and region (Kerang or Mildura), percentage aquatic vegetation cover,
and conductivity. A vertical line has been included to show distributions relative
to zero.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 11: Changes in expected occupancy of the Growling Grass Frog (top) and
the Barking Marsh Frog (bottom) with percentage aquatic vegetation cover.
Conductivity was held constant at a mean value. Solid line indicates posterior
median and dashed lines 95% credible intervals.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 12: Changes in expected occupancy of each species with wetland
conductivity, while holding percentage aquatic vegetation at a mean value. Solid
line indicates posterior median and dashed lines 95% credible intervals. Dashed
red vertical lines indicate 8% seawater.
With the exception of the Growling Grass Frog, all species had strongly negative
relationships with wetland salinity (Figure 10 and Figure 12) and consistent with
that observation, the overall species number was predicted to decline strongly with
increasing salinity (Figure 13). None of the study species were likely to inhabit water
bodies with salinities in excess of approximately 8% seawater or about 4000 EC. The
poor predictive power of conductivity for Growling Grass Frogs probably relates to
their low rates of occupancy in the study area, and their restricted spatial
distributions. Collection of additional data would improve the precision of our
understanding of the relationship between salinity and the probability of occupancy
for this species.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Figure 13: Changes in predicted species number with wetland conductivity, while holding
percentage aquatic vegetation at a mean level. The solid line indicates the posterior
median expected number of species. Dashed lines are 95% credible intervals on the
inferred relationship. Dashed red vertical line indicates 8% seawater.
Example of oxbow lake habitat that supports calling Growling Grass Frog
populations
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
4 Discussion
The Growling Grass Frog and the other late-spring and summer breeding frog fauna of
the Kerang and Mildura regions were surveyed to provide habitat information to support
management of frog habitat within the region. Including the Growling Grass Frog, we
detected seven species, two Hylids and five Myobatrachids. In comparison to the other
species, the Growling Grass Frog was restricted to a few sites within a comparatively
small geographic area and, in the Kerang region, was mostly found in irrigation channels
and farm dams. In the Mildura region, the Growling Grass Frog was only detected in
oxbow lakes and related habitats that had been allocated environmental water. A
previous survey in the Kerang region by Scroggie and Clemann (2003) detected the
Growling Grass Frog in areas that were also surveyed during the present study, but no
Growling Grass Frogs were recorded at these sites during this survey. This result
highlights the notion that Growling Grass Frog populations will vary in their location
over successive breeding seasons, possibly as a consequence of variation in seasonal
conditions. For the management of this species, a clear understanding of the spatial and
temporal dynamics of habitat use are essential as populations of the Growling Grass
Frog typically exists within a spatial mosaic of habitats where particular habitat patches
may be used at different times according to environmental conditions and stochastic
colonisation and extinction events.
Our analysis shows a negative relationship between amphibian richness and water
conductivity (salinity). This finding is consistent with laboratory and field studies of a
number of other frog species which have demonstrated a limited tolerance to salinity
(e.g., Christy and Dickman 2002; Smith et al. 2007). In contrast to our findings, Harley
(2006) detected Growling Grass Frogs and some tadpoles, probably Brown Tree Frog (L.
ewingii), at a wetland with water salinity of around 20% seawater, which is higher than
previously recorded for any Australian species. Clearly, more work is needed to gain a
precise understanding of the salinity tolerance of the Growling Grass Frog. Nonetheless,
our results suggest that management of salinities in frog habitat areas to less than 8% of
seawater levels are desirable for the conservation of the Growling Grass Frog, and for the
persistence of other amphibian species.
Aquatic vegetation has previously been reported as important for a variety of frog
species (Jansen and Healey 2003) and has been associated with the Growling Grass Frog
in particular. We found that two species, the Growling Grass Frog and the Barking Marsh
Frog, were positively associated with the extent of aquatic vegetation, consistent with the
findings of previous studies of this species (for a review, see Clemann and Gillespie In
prep.). We do note, however, that apparently large and healthy populations of both
species were detected in several water bodies that had little or no aquatic vegetation,
suggesting that these habitat conditions are not essential under some circumstances,
and that aquatic vegetation cover may correlate with other, unmeasured, but important
habitat variables. Nonetheless, aquatic vegetation will create structure and habitat within
the water body (Keddy 2002) and is likely to provide cover and refuge from predation.
Aquatic vegetation may also attract insect prey. Accordingly, aquatic vegetation
supplementation is likely to be a positive management action for the Growling Grass
Frog, but needs to be better understood as it is possible that intermediate levels of
vegetation cover may be optimal (Heard pers. comm.). Experimental manipulation of
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
vegetation cover may allow for a better understanding its relationship with habitat
quality.
From an amphibian community perspective, our study highlights the use of a range of
different habitats by the various species. The Barking Marsh Frog was common in most
habitats, with the number of detections generally declining with distance from the
Murray River and decreasing percentage of aquatic vegetation. With the exception of the
Pobblebonk Frog, the other species surveyed during the study were all detected
throughout the various fresh water habitats in the region and were all common and
widespread; suggesting that these species were secure in the study areas at time of
sampling. For most species we did detect a positive, but weak relationship between
occupancy and the extent of aquatic vegetation, indicating that this may be an important
factor in general in determining the distribution of amphibians in the study regions.
The low rates of occupancy for the Growling Grass Frog may be a response to a number
of environmental issues such as drought and habitat availability, but may also be a
feature of the species’ life history. For example, research by Geoff Heard (pers. comm.)
indicates that the species is more likely to occupy habitat within 1 km of a core
population. If this is the case, then the species would be less likely to be detected more
than 1 km from core populations. We suggest that habitat creation, conservation, and/or
restoration may be most likely to be successful if undertaken close to locations where
the Growling Grass Frogs are currently present. A reasonable approach may be to link
isolated populations by creating and/or restoring habitat between areas of known
occupancy. An adaptive management approach (see Schreiber et al. 2004 for a discussion
of the merits and requirements of this approach) may be appropriate if it experimentally
manipulated a range of management actions like changing the extent of aquatic
vegetation and reducing salinity to find optimal levels for the species. Other potential
management actions should be explored such as removal of exotic fish and regulation of
flooding.
A particularly important finding of this project is that the Growling Grass Frog and the
other study species were commonly detected in irrigation channels and farm dams in the
Kerang region. This has clear management implications, as these water bodies are
typically located on private properties, and are primarily managed for purposes other
than conservation of biodiversity. We suggest that management of the Growling Grass
Frog will require continued community support in addition to a detailed understanding
of the specific attributes of these water bodies that are important to the species. Because
the majority of Growling Grass Frog records in the Kerang region were in irrigation
channels, it is likely that there are particular factors that determine the suitability of
these habitats for breeding, such as the extent of aquatic vegetation cover. Other habitat
attributes are also likely be important and may relate to the current dry conditions. In a
period of drought and climate change, these of water bodies may provide critical refuge
habitat (cf. Semlitsch and Bodie 1998).
The survey technique that we used proved to be particularly effective as demonstrated
by the moderate to high detection probabilities for most species. Accordingly, we
confirm a monitoring protocol that can be employed over larger areas. Of critical
importance is repeat surveying the sites over the breeding period, even if the species is
recorded on several previous visits. This allows a probability of presence to be assigned
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
to a “no detection” site. We typically managed to survey between ten and fifteen sites per
night, and little equipment was needed beyond an ability to identify the advertisement
calls of different species. However, continued collection of water chemistry
measurements would help to better determine thresholds for factors like conductivity, if
they exist, but does require specialised equipment. With more sampling sites, other
environmental variables (e.g., turbidity, pH, water permanence, presence of fish) could be
incorporated into the statistical models, helping to refine our understanding of the
environmental requirements of the species. This has clear management benefits as the
quality of habitat creation and restoration efforts will benefit from improved knowledge
of habitat requirements. Inclusion of landscape scale variables (e.g., inter-connectivity of
water bodies) in updated models may also be valuable.
We only collected presence/absence data. Abundance data is often seen as a preferred
value that, if collected properly, could provide better information. However, meaningful
abundance estimates are extremely difficult to obtain for amphibian populations and
would require considerable effort in time and resources (Anderson 2001). Simply
counting the number of individuals that one can find at a site is not a meaningful
estimate of abundance and such values are of extremely limited utility as indices of
abundance for most wildlife populations (Anderson 2001).
4.1 Recommendations
Based upon the survey data collected during this project, we recommend:
• Where possible, the survey effort for the Growling Grass Frog should be include
repeat visits to each site over the breeding season. Depending upon objectives,
simple acoustic surveys (listening for advertisement calls) may provide adequate
distribution and occupancy data. However, visual surveys for the frog may also
be beneficial, and enhance the likelihood of detection (Heard et al. 2006). If
possible, salinity and other physical data should be recorded for inclusion in
statistical habitat models.
• It is unlikely that Growling Grass Frog, or any amphibian species, will inhabit
water bodies with high salinities. Our field data and other published work
suggest that amphibian diversity will decrease drastically beyond salinities of
around 8% seawater (≈ 4000 EC). However, there is limited evidence that some
species may be able to persist under some conditions at up to about 20%
seawater. More information on distribution and salinity will help tighten up
credible intervals, particularly for the Growling Grass Frog.
• More work is needed to better understand the importance of aquatic vegetation.
There is now a growing body of evidence that suggests that the Growling Grass
Frog prefers vegetated water bodies (also refer to Clemann and Gillespie In prep.).
However, large and apparently healthy populations of Growling Grass Frogs do
inhabit water bodies that have little to no aquatic vegetation suggesting that the
presence of aquatic vegetation is not always essential for occupancy. Other
characteristics of water bodies like water depth and seasonality, presence of
exotic predators (e.g., fish, Werner et al. 2007), in addition to broader landscape
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
issues (e.g., inter-connectivity of water bodies, Drielsma et al. 2007) are also likely
to be important.
• The physical properties of irrigation channels and farm dams that allow them to
support populations of Growling Grass Frogs needs to be better understood and
managed. Irrigation channels may provide important habitat for the Growling
Grass Frog (and amphibian biodiversity in general), and if so, must be managed
appropriately. Because the Growling Grass Frog was only detected in a small
percentage of the irrigation channels surveyed, these channels could be managed
to maximize their capacity to provide habitat for the species. Appropriate
management of irrigation channels could have massive on-ground benefits for
the species.
• Habitat construction, conservation and/or restoration efforts in the study regions
should focus within areas where the frog is known to exist and, aim at linking
areas of known occupancy where possible. Utilising adaptive management
techniques (Schreiber et al. 2004), where habitats that surround current
populations are managed in an experimental manner, could be positive way to
not only bolster current populations, but to gain critical information for habitat
management. In addition to systematically varying aquatic vegetation and
salinity, if possible, determining the importance of other habitat components,
such as introduced fish, habitat linkages, and water seasonality would be a
positive outcome of such a project.
• Because much of the habitat that is utilised by the Growling Grass Frog (and
other species) is on private property, conservation of amphibian diversity is likely
to rely upon appropriate and continued public engagement (e.g., brochures, fact
sheets, websites, information sessions) to ensure suitable stewardship of
important habitats by the community and ongoing cooperation between
landholders and resource managers.
The Spotted Marsh Frog (Limnodynastes tasmaniensis).
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
5 References
Alford, R. A., and Richards, S. J. (1999). Global amphibian declines: a problem in applied
ecology. Annual Review of Ecology and Systematics 30, 133-165.
Anderson, D. R. (2001). The need to get the basics right in wildlife field studies. Wildlife
Society Bulletin 29, 1294-1297.
Beebee, T. J. C., and Griffiths, R. A. (2005). The amphibian decline crisis: A watershed for
conservation biology? Biological Conservation 125, 271-285.
Brooks, S. P., and Gelman, A. (1998). General methods for monitoring convergence of
iterative simulations. Journal of Computational and Graphical Statistics 7, 434-
455.
Burnham, K. P., and Anderson, D. R. (2002). 'Model selection and multimodel inference'.
(Springer: New York).
Christy, M. T., and Dickman, C. R. (2002). Effects of salinity on tadpoles of the Green and
Golden Bell Frog (Litoria aurea). Amphibia-Reptilia 23, 1-11.
Clemann, N., and Gillespie, G. R. (In prep.). 'Recovery plan for Litoria raniformis 2004 -
2008'. (Arthur Rylah Institute: Melbourne).
Department of Natural Resources and Environment (2002). 'Victoria's native vegetation
management: A framework for action'. (Department of Natural Resources and
Environment, Victorian Government: Melbourne).
Department of Sustainability and Environment (2003). 'Advisory list of threatened
vertebrate fauna in Victoria'. (Department of Sustainability and Environment:
Melbourne).
Department of Sustainability and Environment (2007). 'Native vegetation guide for
assessment of referred planning permit applications'. (Department of
Sustainability and Environment; Victorian Government: Melbourne).
Drielsma, M., Manion, G., and Ferrier, S. (2007). The spatial links tool: automated
mapping of habitat linkages in variegated landscapes. Ecological modelling 200,
403-411.
Harley, D. (2006). 'An assessment of the Southern Bell Frog (Litoria raniformis)
population at Rocky Swamp in the south east of South Australia'. (Department of
Environment and Heritage: Adelaide).
Heard, G. W., Robertson, P., and Scroggie, M. P. (2006). Assessing detection probabilities
for the endangered growling grass frog (Litoria raniformis) in southern Victoria.
Wildlife Research 33, 557-564.
Jansen, A., and Healey, M. (2003). Frog communities and wetland condition: relationships
with grazing by domestic livestock along an Australian floodplain river. Biological
Conservation 109, 207-219.
Keddy, P. A. (2002). 'Wetland ecology principles and conservation'. (Cambridge University
Press: Cambridge, UK).
MacKenzie, D. I., Nichols, J. D., Royle, J. A., Pollock, K. H., Bailey, L. L., and Hines, J. E.
(2006). 'Occupancy estimation and modelling, inferring patterns and dynamics of
species occurrence'. (Academic Press: London).
National Resource Management Ministerial Council (2004). 'National biodiversity and
climate change action plan'. (Department of Environment and Heritage,
Australian Government: Canberra, ACT).
Schreiber, E. S. G., Bearlin, A. R., Nicol, S. J., and Todd, C. R. (2004). Adaptive
management: a synthesis of current understanding and effective application.
Ecological Management & Restoration 5, 177-182.
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Scott, N. J., and Woodward, B. D. (1994). Surveys at breeding sites. In 'Measuring and
monitoring biological diversity. Standard methods for amphibians' pp 118-125.
(Smithsonian Institution Press: Washington).
Scroggie, M. P., and Clemann, N. (2003). 'Habitat assessment and ecological requirements
of the Growling Grass Frog Litoria raniformis in the area of proposed drainage
works, Benwell-Koondrook Region'. (Arthur Rylah Institute: Melbourne).
Semlitsch, R. D., and Bodie, J. R. (1998). Are small, isolated wetlands expendable?
Conservation Biology 12, 1129-1133.
Smith, M. J., Schreiber, E. S. G., Scroggie, M. P., Kohout, M., Ough, K., Potts, J., Lennie, R.,
Turnbull, D., Jin, C., and Clancy, T. I. M. (2007). Associations between anuran
tadpoles and salinity in a landscape mosaic of wetlands impacted by secondary
salinisation. Freshwater Biology 52, 75-84.
Thomas, A., O'Hara, R., Ligges, U., and Sturtz, S. (2006). Making BUGS open. R News 6, 12-
17.
Thomson, S. A., Littlejohn, M. J., Robinson, W. A., and Osborne, W. S. (1996). Taxonomy of
the Litoria aurea complex: a re-evaluation of the Southern Tableland populations
of the Australian Capital Territory and New South Wales. Australian Zoologist 30,
158-169.
Walker, B., and Salt, D. (2006). 'Resilience thinking, sustaining ecosystems and people in
a changing world'. (Island Press: Washington, USA).
Werner, E. E., Skelly, D. K., Relyea, R. A., and Yurewicz, K. L. (2007). Amphibian species
richness across environmental gradients. Oikos 116, 1697-1712.
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
6 Appendix 1. Sample data sheet
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Frog Species List
Species Present (�)
Visual Calling
Adult Juv. Tad.
Litoria raniformis
Litoria peronii
Crinis signifera
Crinia parinsignifera
Limnodynastes dumerilii
Limnodynastes fletcheri
Limnodynastes tasmaniensis
Other species
Frog Project Survey Form
Site Code
Date
Time
Other Taxa or Tadpoles
Species Preserved (�)
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The Growling Grass Frog and the Late-Spring and Summer Breeding Frogs of North-Western Victoria
Physical and Chemical Measurements
Measurement Value
GPS taken (circle) Yes No
Photograph taken ID Number:
Percentage aquatic vegetation
Water temperature (°C)
Conductivity (μS/cm@25°C)
Turbidity
pH
Other
Other Information
Site name
Road name
Road name, nearest intersection
kilometres and direction from nearest intersection or
other check point
Site type (�) Natural wetland
Natural lake
Farm Dam
Fire Dam
Irrigation channel
Roadside ditch
River
Creek
Oxbow lake
Other
Is the site a modified natural water body? (Yes or
No)
Other comments/Information
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ISBN (print) 978-1-74208-260-8
ISBN (online) 978-1-74208-261-5
ISSN (print) 1835 3827
ISSN (online) 1835 3835
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