The Threatened Growling Grass Frog in the Wimmera and Corangamite Catchments. An Assessment of Habitat Requirements and the Utility of Automatic Call Recording Devices as a Survey Tool

Michael J. Smith, Nick Clemann, Michael P. Scroggie, and Garry N. L. Peterson

2008

Arthur Rylah Institute for Environmental Research

The Threatened Growling Grass Frog in the Wimmera and Corangamite Catchments. An Assessment of Habitat Requirements and the Utility of Automatic Call Recording Devices as a Survey Tool

Michael J. Smith, Nick Clemann, Michael P. Scroggie, and Garry N. L. Peterson

Arthur Rylah Institute for Environmental Research 123 Brown Street, Heidelberg, Victoria 3084

June 2008

Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment. Heidelberg, Victoria.

Report produced by: Arthur Rylah Institute for Environmental Research Department of Sustainability and Environment PO Box 137 Heidelberg, Victoria 3084 Phone (03) 9450 8600 Website: www.dse.vic.gov.au/ari

© State of Victoria, Department of Sustainability and Environment 2008

This publication is copyright. Apart from fair dealing for the purposes of private study, research, criticism or review as permitted under the Copyright Act 1968, no part may be reproduced, copied, transmitted in any form or by any means (electronic, mechanical or graphic) without the prior written permission of the State of Victoria, Department of Sustainability and Environment. All requests and enquires should be directed to the Customer Service Centre, 136 186 or email [email protected]

Citation

Smith, M. J., Clemann, N., Scroggie, M. P., and Peterson, G. N. L. (2008) The Threatened Growling Grass Frog in the Wimmera and Corangamite Catchments. An Assessment of Habitat Requirements and the Utility of Automatic Call Recording Devices as a Survey Tool. Arthur Rylah Institute for Environmental Research. Department of Sustainability and Environment, Heidelberg, Victoria.

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.

Contents

List of tables and figures ...... ii Acknowledgements ...... iii Summary...... iv 1 Introduction...... 6 1.1 Objectives...... 7 2 Methods ...... 7 2.1 General Design ...... 7 2.2 Statistical Analyses ...... 11 2.2.1 Habitat Analysis...... 11 2.2.2 Timer Controlled Cassette Recorders Analysis...... 12 3 Results ...... 13 3.1 Occupancy, Detectability and Habitat Correlates...... 13 3.2 Assessment of the Timer Controlled Call Recorders ...... 16 4 Discussion...... 18 4.1 Recommendations...... 20 5 References...... 22

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List of tables and figures Table 1: Randomly allocated start times for each timer controlled cassette recorder. Each unit was turned on twice daily and recorded for 2 minutes on each occasion...... 11 Table 2: Type and number of water bodies surveyed in the Corangamite and Wimmera catchment management areas (top) and general information on the sites that the Growling Grass Frog was detected in (bottom). The number of sites for each category within which the Growling Grass Frog was detected are also listed. Note that 28 sites were not classified due to access restrictions...... 14

Figure 1: Location of study sites, historical records of the Growling Grass Frog (grey dots), and significant catchment boundaries for Victoria. Catchments that included study sites are named. Sites where the Growling Grass Frog was detected (red circle) or not detected (blue circle) are shown...... 6 Figure 2: Location of timer controlled cassette recorders in the Wimmera and Corangamite catchments...... 10 Figure 3: Faunatech timer controlled cassette recorder showing cassette timer unit (left) and installed microphone (right)...... 10 Figure 4: 2007/2008 survey sites showing water bodies where the Growling Grass Frog was (solid circle) or was not (open circle) detected. Grey dots show historical records...... 15 Figure 5: Posterior means (solid circle) and 95% credible intervals for parameters explaining the relationship between expected occupancy of the Growling Grass Frog and both region and the four environmental variables. The vertical dashed line indicates no effect of the covariate...... 16 Figure 6: Predicted relationships (solid) and 95% credible intervals (dashed lines) between the predicted probability of occupancy by Growling Grass Frogs and proportion of aquatic vegetation, conductivity, proportion canopy cover, and distance to the nearest woodland. Region was randomly set to a value of four (North Central CMA) for each prediction. When not a focal predictor variable, proportion aquatic vegetation was set to 0.6, conductivity to 0.05 EC, proportion canopy cover to 0.1, and distance to nearest forest to 5 km...... 17 Figure 7: Predicted relationship between median posterior probability of detection (solid line) ± 95% credible intervals (dashed lines) and number of recordings...... 17

ii

Acknowledgements This project was funded by the Australian Federal Government’s National Heritage Trust via the Corangamite and Wimmera Catchment Management Authorities, and the Department of Sustainability and Environment, Biodiversity Group, South West Region. We especially thank Lauren Dodd and Ruth Lennie for their contributions to the project.

iii

Summary

An intensive survey for the Growling Grass Frog in the Wimmera and Corangamite catchments during late spring and summer of 2007/2008 was conducted to address three High Priority Actions from the Victorian State Government Department of Sustainability and Environment Actions for Biodiversity Conservation database (ABC). These Actions are also Recovery Plan Actions as outlined in the draft recovery plan for the species. The major Actions to be addressed by this research were to undertake habitat monitoring to examine and identify key habitat parameters at Growling Grass Frog sites and to test automatic call recording devices as a technique to survey and monitor the species. Conducting surveys using recognised survey techniques to determine extent and abundance of populations is a High Priority Action for the species. The project also addresses the High Priority Actions to conduct surveys to confirm existing records.

The surveys were conducted within the Corangamite and Wimmera Catchment Management regions in areas with historical records of the Growling Grass Frog. We detected Growling Grass Frogs in eleven of eighty survey sites. Fourteen of the survey sites were near to historical sites and the Growling Grass Frog was detected in five of these sites.

Due to imperfect probabilities of detection, effective monitoring of the Growling Grass Frog will require repeated surveys during appropriate times to estimate probabilities of occupancy when the species is not detected, and to provide valid inferences regarding the relationships between habitat attributes and probability of occupancy. With proper application, automated call recording devices can achieve detectabilities of around 0.75 for calling males. Accordingly, with correct installation, automated call recording devices can provide a robust survey and monitoring tool for presence/absence information that will be cost and time effective.

Growling Grass Frogs occupied a variety of freshwater habitats that included still sections of creeks, farm dams, irrigation channels, and fire water dams. Occurrences of the Growling Grass Frog were positively associated with the extent of aquatic vegetation cover (emergent and/or submerged) and the distance to the nearest woodland and negatively associated with water conductivity and proportion of tree canopy cover around the site. Our data shows that Growling Grass Frogs readily inhabit wetlands in rural landscapes with little to no tree cover.

In line with the actions from the draft Growling Grass Frog National Recovery Plan and actions from the ABC, we recommend continued surveys for the species to maintain up-to- date knowledge of the species distribution and to facilitate the location of important populations. Population genetic techniques should be used to better understand metapopulation structures for the species and to identify important source populations. Once identified, important populations should be monitored. The impacts of a range of threatening processes, such as habitat modification and climate change, can only be assessed with on-going population monitoring.

Based upon the results reported here, we recommend experimental manipulation of key habitat variables to better understand the management and restoration of habitat for the Growling Grass Frog. For example, our data suggests that supplementation of aquatic

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vegetation may be an effective management action for the species, but appropriate levels of revegetation need to be determined. We suggest that the removal of weed tree species around sites may also be a valuable restoration activity.

v The Growling Grass Frog in the Wimmera and the Corangamite

1 Introduction The continued decline and extinction of many amphibian taxa across the globe is an ongoing conservation concern (Alford and Richards 1999). In Australia, 47 frog species are currently listed as Threatened or Endangered under the International Union for Conservation of Nature (IUCN) Global Amphibian Assessment guidelines (cf. Hero and Morrison 2004). Included in this list is the Growling Grass Frog (Litoria raniformis), which was historically known to occur throughout much of Victoria (Figure 1), but has shown marked population declines in recent decades (Heard et al. 2006). The Growling Grass Frog is listed as Endangered under the IUCN Red List (IUCN 2000), Vulnerable nationally under the Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act), and Endangered in Victoria (Department of Sustainability and Environment 2003). The threatening processes that have driven these declines are still poorly understood, but are likely to include chytridiomycosis (Alford and Richards 1999) and habitat modification and degradation (Clemann and Gillespie in prep.).

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Figure 1: Location of study sites, historical records of the Growling Grass Frog (grey dots), and significant catchment boundaries for Victoria. Catchments that included study sites are named. Sites where the Growling Grass Frog was detected (solid black circle) or not detected (open circle) are shown.

Only limited and, often, anecdotal information exists regarding the habitat requirements of the Growling Grass Frog (but see Heard et al. in press). These requirements include an apparent association with still or slow moving water with extensive aquatic vegetation. The Growling Grass Frog is commonly found in degraded habitats in rural settings that includes areas threatened by secondary salinisation; an impact that can render habitat unsuitable for amphibians (Smith et al. 2007), as suggested for the closely related Litoria

6 The Growling Grass Frog in the Wimmera and the Corangamite

aurea (Christy and Dickman 2002). The Growling Grass Frog is also typically recorded in habitats with little to no tree cover (M. Smith pers. obs.). Identifying habitat features associated with the persistence of the Growling Grass Frog should not only be valuable from a general conservation management perspective (Semlitsch 2000), but will also provide guidance for habitat restoration projects. We are optimistic that habitat restoration can benefit the Growling Grass Frog, as their persistence in rural agricultural landscapes suggests that modified and/or created water bodies can provide viable habitat under some circumstances.

1.1 Objectives We undertook a detailed survey for the Growling Grass Frog across two catchment management areas (Wimmera and Corangamite) to address three High Priority actions identified in the Department of Sustainability and Environment Actions for Biodiversity Conservation database (ABC). These Actions are also Recovery Plan Actions as outlined in the draft recovery plan for the species (Clemann and Gillespie in prep.). The major Actions we address are: 1) Undertake habitat monitoring to examine and identify key habitat parameters at Growling Grass Frog sites,

2) Test automatic call recording devices as a survey and monitoring technique to address the ABC Action to conduct surveys using recognised survey techniques to determine extent and abundance of populations.

3) Conduct surveys to assess historical records.

By identifying habitat features associated with the occurrence of the Growling Grass Frog, the project will also provide information to direct future habitat restoration projects that are proposed within the study areas.

2 Methods 2.1 General Design Although this study focuses on the Corangamite and Wimmera catchments (Figure 1), we include previously collected data from North East catchment management area (2007- 2008 season, 7 sites), the North Central catchment management area (2006 – 2007 season, 61 sites), and the Mallee catchment management area (2006 – 2007 season, 16 sites). A description of the data collection and study sites for the Mallee and North Central catchment management areas can be found in Smith et al. (2008). By including extra data, we were able to extend the statistical modelling to include more predictor variables (see section 2.2). Accordingly, the study was conducted over two Growling Grass Frog breeding seasons (October to January 2006/07 and 2007/08), and encompassed a considerable portion of the species’ historical range in Victoria (Figure 1).

Roads within the historical distribution of the Growling Grass Frog were chosen haphazardly, and driven during the day. Potential sites (wetlands, dams, lakes, and still

7 The Growling Grass Frog in the Wimmera and the Corangamite

sections of streams and irrigation channels) were identified for later surveying. These sites included 14 that were within 1.5 km of historical records. A value of 1.5 km was chosen to delineate areas as historically occupied, because surveying for historical sites can be problematic for the Growling Grass Frog. For example, Growling Grass Frogs have a life history that is characterised by local colonisation and extinction within a range of around 1km of source populations in urban areas (Heard pers. comm.) or within 10 km in more agricultural landscapes (Wassens et al. 2007). Accordingly, we would expect a Growling Grass Frog population to make varied use of local habitats and to not always be present in a particular water body. Additionally, the continued drought conditions means that many historical records are in aquatic systems that are currently dry. It is reasonable to expect that remaining frogs from those populations will make use of nearby water bodies if they still occur in the area.

To assess habitat requirements for the Growling Grass Frog, 164 study sites were surveyed for adult frogs using one of three survey protocols. Protocol 1 involved listening for 10 minutes for frog advertisement calls during nocturnal hours (21:30 to 03:00 Australian Eastern Standard Time) and was used during 39 site visits. Protocol 2 involved nocturnal call surveys for 10 minutes followed by a visual torch-light survey for a minimum of 10 minutes and was used during 222 site visits. Protocol 3 involved diurnal call surveys (12:00 to 20:00 AEST) for 10 minutes followed by a visual survey for a minimum of 10 minutes and was used during 25 site visits. Heard et al. (2006) indicated that multiple surveys are necessary for adequate detection of the Growling Grass Frog, and, accordingly, we repeat-surveyed as many sites as possible. Seventy nine sites were surveyed once, 48 on two occasions, and 37 sites were surveyed three times.

We measured four habitat predictor variables at each site: proportional cover of aquatic vegetation, conductivity of water, proportion of riparian tree canopy cover and distance to the nearest woodland (see below for an explanation). Based upon current knowledge of the habitat preferences of the Growling Grass Frog, these variables were considered likely to influence occupancy by the species, and to have implications for management actions in Victoria. For example, human induced, or secondary, salinisation is a major environmental issue in Victoria (Russ 1995) that is known to be a threatening process for amphibians (Smith et al. 2007). Tree planting is a common management practice in Victoria (e.g., Heuperman 1999), but there is little consideration of its impact on amphibians.

Not all variables could be measured at each site due to factors such as missing aerial photograph coverage (see below) and lack of access to sites on private property. Water conductivity (EC: mS cm-1 @25°C) was measured at 126 sites using a TPS 90FL multi- parameter meter. Electrical conductivity measurements were made within 15 cm of the water surface. We estimated the extent of aquatic vegetation (both emergent and submerged plants) at 120 sites by approximating the proportion of the water body surface area that contained floating, emergent, and submerged aquatic vegetation. Where the water body was linear (e.g., section of a stream or irrigation channel), we estimated the extent of aquatic vegetation along a 100 m section that was centred on the survey point. Where water bodies were particularly large (e.g., lakes), aquatic vegetation was estimated within 50 m of either side of the survey point and within 50 metres of the shoreline.

8 The Growling Grass Frog in the Wimmera and the Corangamite

To determine the distance to the nearest woodland, we used the TREE100 layer (provided by the Victorian Department of Sustainability and Environment, Australia) that was derived from LANDSAT digital data from 1993. This is the most current data source and although it is 15 years old still accorded well with our observations in the field. We define a woodland as any tree cover that constituted woody vegetation greater than 2 m in height with a crown cover greater than 10% that covered an area equal to or greater than 0.5 km2. The Nearest Features extension (version 3.8b; http://www.jennessent.com/arcview/nearest_features.htm) was used within ArcView GIS (version 3.3) to measure the distance in kilometres from each study site to the nearest woodland polygon edge.

We used aerial photographs in ArcView GIS (version 3.3) to estimate the area of riparian tree canopy cover within a 100 m radius of the survey point at 157 sites. Proportion of canopy cover was calculated as the area of tree cover (m2) divided by 31415 m2 (the area of a circle with a 100 m radius). Aerial photographs were taken between 2001 and 2004, and varied in pixel size from 0.3 to 2.5 m.

In addition to a quantitative assessment of the habitat requirements of the species, we present a brief appraisal of the Ecological Vegetation Classes (EVC) and aquatic habitat types that the Growling Grass Frog was detected in within the Corangamite and Wimmera catchment management areas. Refer to Smith et al. (2008) for more information on the EVCs and aquatic habitat use by the Growling Grass Frog in the North Central and Mallee catchment management areas.

Faunatech timer controlled cassette recorders (faunatech.com.au) were trialled at 18 sites during the 2007/2008 breeding season (Figure 2) to determine their suitability as a survey tool for the Growling Grass Frog. These call recording devices consist of a cassette recorder, battery, and timer circuit enclosed in a weather proof container (Figure 3). An external microphone is attached to the unit via a weather proof connection (Figure 3). Cassette tapes that had a 60 minute recording capacity were used. Recorders were set to record for two minutes on two occasions each day between 20:00 and 01:00 hours AEST. Recording times varied among recorders (Table 1).

9 The Growling Grass Frog in the Wimmera and the Corangamite

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Figure 2: Location of timer controlled cassette recorders (solid black circle) in the Wimmera and Corangamite catchment management areas.

Figure 3: Faunatech timer controlled cassette recorder showing cassette timer unit (left) and installed microphone (right).

10 The Growling Grass Frog in the Wimmera and the Corangamite

Table 1: Randomly allocated start times for each timer controlled cassette recorder. Each unit was turned on twice daily and recorded for 2 minutes on each occasion. Unit Start time 1 Start Time 2 1 22:00 23:00 2 22:00 0:00 3 21:00 23:00 4 21:00 23:00 5 21:00 23:00 6 21:00 23:00 7 21:00 0:00 8 22:00 23:00 9 22:00 0:00 10 22:00 0:00 11 22:00 23:00 12 21:00 22:00 13 20:00 1:00 14 22:00 1:00 15 23:00 1:00 16 22:00 23:00 17 23:00 0:00 18 23:00 0:00

2.2 Statistical Analyses 2.2.1 Habitat Analysis As it could not be assumed that Growling Grass Frogs actually present at a site would 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). This approach treats the sites under consideration as being drawn from two discrete categories: occupied sites, where on each survey 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 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 that 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 likely be recorded during the course of a set of surveys at an occupied site. Using Bayesian or maximum likelihood methods, 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.

11 The Growling Grass Frog in the Wimmera and the Corangamite

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, through the use of logistic regression equations within the statistical model, which relate the probabilities of occupancy or detection to the covariate values. In the present case, we related the probabilities of occupancy by the Growling Grass Frog to habitat variables measured at the sites. We included four environmental predictor terms, a term to account for effects related to sampling over two breeding seasons, and terms to account for catchment effects (hereafter referred to as region) in the model.

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 (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 obtained using conventional maximum likelihood inferences. The covariates were log transformed and centred on their means prior to analysis to improve model fit. 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 5000 iterations and retaining the next 95000 iterations for further inference.

Inferences regarding derived quantities, which are functions of the model’s parameters, were readily made 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 probability of occupancy by the Growling Grass Frog that would be expected under representative sets of covariate values (cf. Smith et al. 2007).

2.2.2 Timer Controlled Cassette Recorders Analysis The capacity of each recording made by the timer controlled cassette recorders to detect Growling Grass Frogs was modelled using a logistic regression model within a Bayesian framework. In this case, one centred predictor variables was included, time of recording. For this analysis, the logistic regression was constructed such that the probability of detection for each recording was estimated relative to the predictor variable.

We used the equation:

P =1-(1-p)N N

12 The Growling Grass Frog in the Wimmera and the Corangamite

to determine the overall detection probability of the units relative to the number of recordings. p = detection probability of individual recordings and N = number of recordings.

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 5000 iterations and retaining the next 95000 iterations for further inference.

3 Results 3.1 Occupancy, Detectability and Habitat Correlates Eighty sites were surveyed in the Wimmera and Corangamite catchment management areas (36 and 44 respectively; Figure 4) resulting in a total of 164 survey sites across the five catchments. Across all of the study regions, the Growling Grass Frog was detected in 39 different sites which included five in the Corangamite and six in the Wimmera catchment (Figure 4).

The Growling Grass Frog was detected in five of the 14 survey sites that were within 1.5 km of historical records (Figure 4). Seven of the Growling Grass Frog sites in the Wimmera and Corangamite were on private property and four were on public land. In these two catchment management areas, the Growling Grass Frog was detected in a range of water bodies, including natural wetlands, farm dams, fire water dams, and irrigation channels (Table 2). Only one Growling Grass Frog site occurred in habitat that had an EVC classification (175 Grassy Woodland). The remaining sites were in areas without mapped EVC data.

Detection probabilities for the Growling Grass Frog differed between the three survey methods. Detection was lowest using the nocturnal call and visual survey technique ( X = 0.62 (0.40 – 0.78 CI)), intermediate using diurnal call and visual survey method ( X = 0.73 (0.26 – 0.99 CI)), and best with the nocturnal call survey protocol ( X = 0.78 (0.40 – 0.99 CI)). It is important to note that we used protocols 1 and 3 on far fewer occasions than protocol 2 and as a consequence, there is greater uncertainty surrounding these estimates. Both the non-random assignment of sites to survey protocols and the local environmental conditions were more likely to influence detection probabilities under protocols 1 and 3. The most broadly used protocol (2) provided detection probabilities that are consistent with those reported by Heard et al. (2006) when using similar survey methods.

Occupancy by the Growling Grass Frog related strongly and positively to the proportion of aquatic vegetation cover and distance to the nearest woodland, and strongly and negatively to the proportion of riparian tree canopy cover and conductivity (Figure 5 and Figure 6). Rates of occupancy differed among regions (Figure 5), but we failed to find any relationship between occupancy and breeding season ( X = 2.1 ± 5.1 CI) and accordingly removed that variable from the final model.

13 The Growling Grass Frog in the Wimmera and the Corangamite

Table 2: Type and number of water bodies surveyed in the Corangamite and Wimmera catchment management areas (top) and general information on the sites that the Growling Grass Frog was detected in (bottom). The number of sites for each category within which the Growling Grass Frog was detected are also listed. Note that 28 sites were not classified due to access restrictions. Water Body Type No surveyed No with Growling Grass Frogs detected Stream 5 1 Natural wetland 12 3 Water treatment reserve 1 1 Irrigation channel and drain 10 2 Farm dam 13 3 Fire dam 11 1 Region Type Latitude Longitude Corangamite Farm Dam -38.10 143.26 Corangamite Irrigation Channel -37.90 143.68 Corangamite Irrigation Channel -38.08 143.64 Corangamite* Stream -37.89 143.73 Corangamite* Wetland -38.33 144.33 Wimmera Farm Dam -37.07 141.27 Wimmera Farm Dam -37.01 141.19 Wimmera* Fire Dam -36.73 141.38 Wimmera Sewage Work -37.02 141.31 Wimmera* Wetland -36.97 141.03 Wimmera* Wetland -36.97 141.03 * denotes a site where Growling Grass Frogs have been recorded in the past.

14 The Growling Grass Frog in the Wimmera and the Corangamite

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Figure 4: 2007/2008 survey sites showing water bodies where the Growling Grass Frog was (solid black circle) or was not (open circle) detected. Grey dots show historical records.

15 The Growling Grass Frog in the Wimmera and the Corangamite

Figure 5: Posterior means (solid circle) and 95% credible intervals for parameters explaining the relationship between expected occupancy of the Growling Grass Frog and both region and the four environmental variables. The vertical dashed line indicates no effect of the covariate.

3.2 Assessment of the Timer Controlled Call Recorders In general, the timer controlled call recorders worked well. We failed to detect any relationship between the ability of the equipment to detect calls of the Growling Grass Frog and time of recording (posterior mean = 0.24 (-0.60 – 1.11 CI)). The predictor variable was removed for the final model.

Even though the probability of detection was only 0.01 (0.005 – 0.02 CI) for a 2 minute recording, 120 recordings is predicted to have a probability of detection in the order of 0.75 (Figure 7).

16 The Growling Grass Frog in the Wimmera and the Corangamite

Figure 6: Predicted relationships (solid) and 95% credible intervals (dashed lines) between the predicted probability of occupancy by Growling Grass Frogs and proportion of aquatic vegetation, conductivity, proportion canopy cover, and distance to the nearest woodland. Region was randomly set to a value of four (North Central CMA) for each prediction. When not a focal predictor variable, proportion aquatic vegetation was set to 0.6, conductivity to 0.05 EC, proportion canopy cover to 0.1, and distance to nearest woodland to 5 km.

Figure 7: Predicted relationship between median posterior probability of detection (solid line) ± 95% credible intervals (dashed lines) and number of recordings.

17 The Growling Grass Frog in the Wimmera and the Corangamite

4 Discussion Our results suggest that water bodies with low salinity levels, a high proportion of aquatic vegetation, and minimal canopy cover are most likely to be occupied by the Growling Grass Frog during the breeding season in Victoria. By examining the relationships between the occupancy of the Growling Grass Frog and the four environmental variables, we provide a basis for future habitat management. In the two focal catchment management areas, we found Growling Grass Frogs in a range of habitats that included natural wetlands, streams, irrigation channels, and farm dams, but the species was detected in areas within 1.5 km of historical records in five out of fourteen occasions.

A negative relationship between amphibian diversity and canopy cover has been previously observed for other species (e.g., Werner et al. 2007), and explanations of this phenomenon usually consider issues relating to resource availability and quality for tadpoles. Our findings suggest that reducing canopy cover may be an appropriate management action for the species. However, we do not recommend the removal of indigenous tree species, and we encourage well-considered tree planting projects (Heuperman 1999), as they often have broader values. We suggest that the removal of weed tree species, such as Willow, is likely to be a beneficial management action for the Growling Grass Frog, and believe that this issue warrants further investigation.

The effects of salinity on frogs are becoming better understood, and the negative relationship between the occurrence of the Growling Grass Frog and salinity that we detected accords with results for other amphibian species (Christy and Dickman 2002; Chinathamby et al. 2006; Smith et al. 2007). In addition to any toxological impacts on development and survival, increasing salinities are likely to reduce plant and insect diversity (James et al. 2003), possibly affecting the prey and habitat of the Growling Grass Frog. Because we only measured presence/absence of adults, salinity may have a greater impact than would be detected with our methods. For example, population sizes and or individual fitness may decrease as a consequence of increasing salinities, but would not be detected in this study. Experimentally determining the upper limit of salinity tolerances for Growling Grass Frog eggs and tadpoles (cf. Christy and Dickman 2002; Chinathamby et al. 2006) would be particularly useful in terms of the conservation management for the species, as would developing a better understanding of the effects of increasing salinity on post-metamorphic survival and fitness.

The positive association between the Growling Grass Frog and aquatic vegetation cover is consistent with studies of other species (e.g., Pavignano et al. 1990; Qian et al. 2007). A number of mechanisms have been suggested as explanations for these relationships, including improved tadpole survivorship due to the provision of refuges from predators (Babbit and Tanner 1997). The management of aquatic vegetation within Growling Grass Frog habitat will provide an opportunity to test functional explanations for the relationship with vegetation cover and to determine critical levels of vegetation cover. Because wetland restoration ecology has a history of vegetation supplementation, approaches with a strong theoretical basis have been developed (Mitsch and Wilson 1996; Suding et al. 2004) that could guide habitat restoration for the Growling Grass Frog.

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Within the current distribution of the Growling Grass Frog, many extant sites occur on privately owned and managed land in an agricultural landscape, rather than within conservation reserves. Consequently, conserving the Growling Grass Frog will require the persistence of the species in water bodies that are subjected to a variety of land use practices (cf. Jansen and Healey 2003), such as cropping of adjacent areas, and grazing and trampling by domestic stock. However, with increasing habitat degradation and the possibility of a range of threatening processes acting in synergy (Semlitsch 2000), it cannot be assumed that currently occupied sites are viable in the longer-term. Consequently, on-going monitoring of populations and their habitat is essential.

The occurrence of the Growling Grass Frog in rural landscapes provides considerable opportunity for habitat restoration. Research by Heard (in prep.) indicates that the species relies upon mosaics of viable habitat within which occupancy is more likely within a kilometre-scale radius of large source populations. We suggest that rehabilitation efforts should involve manipulation of habitat variables in and around aquatic habitats that are in close proximity (less than one kilometre) to known populations. Canopy cover could be reduced and aquatic vegetation can be supplemented (cf. Mitsch and Wilson 1996). Under some circumstances there may be scope to reduce water salinity. An adaptive approach could be appropriate if it modelled alternative management options, identified decision structures, and incorporated appropriate monitoring and evaluation (see Schreiber et al. 2004 for a detailed description of adaptive management).

Finally, we utilised three different sampling protocols during the habitat study and trialled automatic call cassette recording equipment. Two of the survey protocols (1 and 3) used during the study, were not used on many occasions and accordingly, more data is needed to improve our confidence in the detectability of these protocols for the Growling Grass Frog. Protocol 2 (nocturnal acoustic survey followed by visual torch light survey), was used across all regions and in both seasons and was comparable to the results of Heard et al. (2006). Our results confirm the need for repeated surveys to take into account uncertainty related to non-detection in occupied sites (e.g., Heard et al. 2006; MacKenzie et al. 2006; Brown et al. 2007).

The automatic call recording protocol appears to be a valid survey/monitoring tool for presence/absence if used appropriately. Based upon our experiences, there are a number of benefits and limitations in the use of automated call recording equipment as a survey technique. They include:

Benefits: 1) Reasonable detection probability if installed over an appropriate period of time (≈ 120 recordings). 2) Cost and time effective. - Unit cost approximately $500. - 1.2 hour cassettes cost around $2 each, but can be reused (note, we have now developed a digital version with solid state reusable storage). - Installation of the units is quick and easy and the equipment can be left in the field for at least one month without battery changes. Recording duration will depend upon a combination of time settings and cassette length.

19 The Growling Grass Frog in the Wimmera and the Corangamite

- Digitising and analysing recordings takes approximately 15 minutes/cassette and requires appropriate software (approx. cost = $300; however, freeware software is available). We are trialling software that automatically detects frog calls in the recordings. If successful, this software will significantly reduce analysis time. 3) Limited skills required to install equipment. 4) The recorders can readily detect frogs within a radius of approximately 50m of the installation point.

Limitations: 1) Equipment failure can result in loss of data. Failure can result from poor installation, heat damage if unit is not appropriately shaded, damage from animals gnawing the cable, and theft (however, we did not lose any units to theft during this study). Installation mistakes can be reduced with appropriate training. 2) There is a need to increase the number of units with larger survey areas.

4.1 Recommendations 1) Continued surveys (Recovery Plan Action 2.1 and High Priority ABC Action). Up-to-date and accurate distributional information is essential for all aspects of the management of the Growling Grass Frog and has been identified as an important action by the draft recovery plan for the species (Clemann and Gillespie in prep.).

• In addition to information collected by community-based volunteer groups, targeted surveys by suitably qualified amphibian biologists are necessary. All information should be loaded onto the Victorian Fauna Database (http://www.viridans.com/FISVFD/VFD1.HTM).

• Due to imperfect detection, effective monitoring of the Growling Grass Frog will require repeated surveys during appropriate times to estimate probabilities of occupancy when the species is not detected, and to provide valid inferences regarding the relationships between habitat attributes and probability of occupancy. Nocturnal acoustic surveys followed by spotlight searches should provide adequate distribution and occupancy data. Automatic call recording equipment should also be utilised where possible. If possible, salinity and other physical data should be recorded for inclusion in statistical habitat models.

• Surveying could also aid in the collection of information to identify important populations and to better understand the metapopulation structure of the species which is a Priority Action in the Recovery Plan and in ABC. Genetic techniques are now available to identify important source populations (cf. Manier and Arnold 2005). However, collection of genetic material may under some circumstances require appropriate ethics approval.

• Access to privately owned sites will be critical for successful surveying, monitoring, and habitat management; fostering community support and awareness is also a Priority Action for ABC. Accordingly, appropriate and continued public engagement (e.g., brochures, fact sheets, websites, information

20 The Growling Grass Frog in the Wimmera and the Corangamite

sessions) to ensure suitable stewardship of important habitats by the community and ongoing cooperation between landholders and resource managers will be essential.

2) Monitoring (Recovery Plan Action 2.2 and High Priority ABC Action) Once identified, important populations should be monitored. With ongoing threatening processes, such as habitat modification and climate change, rates of occupancy are likely to fluctuate.

• Our initial findings suggest that automated call recorders provide one viable monitoring tool for calling Growling Grass Frog. The equipment needs to be installed carefully and there is a possibility of theft. More testing of these units should provide more optimal recording times and durations.

3) Habitat management (Recovery Plan Action 1.1 and High Priority ABC Action) Habitat construction, conservation and/or restoration should focus on areas where the frog is known to exist and aim to linking areas of known occupancy where possible.

The DSE Biodiversity Group, South West Region, in conjunction with the Arthur Rylah Institute for Environmental Research and the Corangamite and Wimmera CMAs is currently investigating habitat management options for the species. One project is focusing on unoccupied farm dams in the vicinity of water bodies that are occupied by the Growling Grass Frog. Aquatic vegetation supplementation and the creation of riparian refuge habitat (fenced-off area with rocks and logs) is being trialled to encourage natural colonisation.

• The physical properties of irrigation channels and farm dams that allow them to support populations of Growling Grass Frogs need to be better understood and managed. These water bodies may provide important habitat for the Growling Grass Frog (and amphibian biodiversity in general), and if so, should be managed to maximise their capacity to provide habitat for the species.

• Other characteristics of water bodies such as water depth and seasonality, presence of exotic predators (e.g., fish, Werner et al. 2007), and broader landscape features (e.g., inter-connectivity of water bodies, Drielsma et al. 2007) are also likely to be important and should be further assessed.

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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. Babbit, K. J., and Tanner, G. W. (1997). Effects of cover and predator identity on predation of Hyla squirella tadpoles. Journal of Herpetology 31, 128-130. Brooks, S. P., and Gelman, A. (1998). General methods for monitoring convergence of iterative simulations. Journal of Computational and Graphical Statistics 7, 434- 455. Brown, G. W., Scroggie, M. P., Smith, M. J., and Steane, D. (2007). An evaluation of methods for assessing the population status of the threatened alpine tree frog (Litoria verreauxii alpina) in southeastern Australia. Copiea 2007, 765-770. Chinathamby, K., Reina, R. D., Bailey, P. C. E., and Lees, B. K. (2006). Effects of salinity on the survival, growth and development of tadpoles of the brown tree frog, Litoria ewingii. Australian Journal of Zoology 54, 97-105. 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 Sustainability and Environment (2003). 'Advisory list of threatened vertebrate fauna in Victoria'. (Department of Sustainability and Environment: 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. 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. Heard, G. W., Robertson, P., and Scroggie, M. P. (in press). Microhabitat preferences of the endangered Growling Grass Frog Litoria raniformis in southern Victoria. Australian Zoologist. Hero, J.-M., and Morrison, C. (2004). Frog declines in Australia: Global implications. Herpetological Journal 14, 175-186. Heuperman, A. (1999). Hydraulic gradient reversal by trees in shallow water table areas and repercussions for the sustainability of tree-growing systems. Agricultural Water Management 39, 153-167. IUCN (2000). 'IUCN Red List Categories'. (IUCN Species Survival Commission: Gland, Switzerland). James, K. R., Cant, B., and Ryan, T. (2003). Responses of freshwater biota to rising salinity levels and implications for saline water management: a review. Australian Journal of Botany 51, 703-713. 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. 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). Manier, M. K., and Arnold, S. J. (2005). Population genetic analysis identifies source-sink dynamics for two sympatric garter snake species (Thamnophis elegans and Thamnophis sirtalis). Molecular Ecology 14, 3965-3976. Mitsch, W. J., and Wilson, R. F. (1996). Improving the success of wetland creation and restoration with know-how, time, and self-design. Ecological Applications 6, 77-83. Pavignano, I., Giacoma, C., and Castellano, S. (1990). A multivariate analysis of amphibian habitat determinants in north western Italy. Amphibia-Reptilia 11, 311-324. Qian, H., Wang, X., Wang, S., and Li, Y. (2007). Environmental determinants of amphibian and reptile species richness in China. Ecography 30, 471-482. Russ, P. (1995). 'The salt traders: a history of salinity in Victoria'. (The Department of the Premier and Cabinet, State of Victoria: Melbourne).

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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. Semlitsch, R. D. (2000). Principles for management of aquatic-breeding amphibians. Journal of Wildlife Management 64, 615-631. 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. (2007). Associations between anuran tadpoles and salinity in a landscape mosaic of wetlands impacted by secondary salinisation. Freshwater Biology 52, 75-84. 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: Melbourne). Suding, K. N., Gross, K. L., and Houseman, G. R. (2004). Alternative states and positive feedbacks in restoration ecology. Trends in Ecology & Evolution 19, 46-53. Thomas, A., O'Hara, R., Ligges, U., and Sturtz, S. (2006). Making BUGS open. R News 6, 12- 17. Wassens, S., Roshier, D. A., Watts, R. J., and Robertson, A. I. (2007). Spatial patterns of a Southern Bell Frog Litoria raniformis population in an agricultural landscape. Pacific Conservation Biology 13, 104-110. 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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