For Use by Major Mitchell's Cockatoo (Lophochroa Leadbeateri) in Pine Plains, Wyperfeld National Park

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Simulating natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri):

A report to the Department of Environment and Primary Industries

Report Title: “Simulating natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri): A report to the Department of Environment and Primary Industries.”

Prepared by: Dr Victor G. Hurley Senior Strategic Fire and Biodiversity Officer Department of Environment and Primary Industries 308-390 Koorlong Ave Irymple VIC 3498 Email: [email protected] Telephone: 5051 4610

And

Grant J. Harris Ironbark Environmental Arboriculture Charles Street Fitzroy Melbourne VIC 3065 ABN: 14 667 974 300 Email: [email protected] Telephone: 0415 607 375

Report Status: Final 21 December 2014

 The State of Victoria Department of Environment and Primary Industries Melbourne 2014 This publication is copyright. No part may be reproduced by any process except in accordance with the provisions of the Copyright Act 1968.

This document may be cited as: Hurley, V.G. and Harris, G.J., (2014) “Simulating natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri): A report to the Department of Environment and Primary Industries.”

Cover photographs: Hauling new cavity cover plate with the elevated work platform (Grant Harris ©).

ACKNOWLEDGMENTS

This project was funded by the Victorian Environmental Partnerships Program (VEPP) in 2013-15. Thanks go to David Christian and Matthew Baker for arranging logistical support and access to Parks Victoria facilities. Much appreciation to Ewan Murray who worked in the field in collecting and recording data and capably wielding the chainsaw and chipper and for field and occasional ambulance assistance. Special thanks to FM Watson for recreating a usable Style Guide and K Learmonth and N Schedvin for proof reading and providing valuable comment on a late draft of the document.

This work is licensed under a Creative Commons Attribution 3.0 Australia licence. You are free to re-use the work under that licence, on the condition that you credit the State of Victoria as author. The licence does not apply to any images, photographs or branding, including the Victorian Coat of Arms, the Victorian Government logo and the Department of Environment and Primary Industries logo. To view a copy of this licence, visit http://creativecommons.org/licenses/by/3.0/au/deed.en

ISBN: 978-1-74146-443-6 pdf

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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.

Contents

Contents 2

List of figures 3 List of tables 3

Executive Summary 4

Introduction 4 Project Objectives/Outcomes 4 Conclusion 4 Recommendations 5

Introduction 6

Background 6 Project Objectives 7

Methods 8

Tree selection 9 Cavity dimensions 11

Results 12

Statistics 12

Discussion 14

Recommendations 15

References 18

Appendix I 16

Box plots of tree and cavity measurements 16

Comparing simulated natural cavities to natural cavities in Callitris

List of figures

Figure 1. The future of Victoria’s largest Major Mitchell’s Cockatoo breeding population depends upon the successful development of techniques to form cavities in Callitris to simulate natural cavities...... 5 Figure 2. Counts of nest sites used by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri) at Pine Plains, Wyperfeld National Park from 1995 to 2014.  = Annual count of nest trees remaining.  = count of remaining nest trees (March 2014). Black trend line = linear regression, R2 = 0.894...... 7 Figure 3. Conceptual time line of tree growth and appropriate growth stages for SNC intervention. Letters represent the location of SNC techniques in the temporal sequence of large old tree development and loss. I = Initiate, E = Excavation, A = Augmentation and R = Restoration...... 9 Figure 4. Decision matrix for the selection of the appropriate technique in simulated cavity formation in Slender Callitris Pine (Callitris gracilis murrayensis). Diamonds are decision points and light orange boxes are actions. The orange strips represent recording and monitoring activities. The pale orange rectangles represent actions or SNC techniques...... 10 Figure 5. Measurements of naturally occurring Major Mitchell’s Cockatoo nest cavities in Callitris tree trunks (n = 55) (figure adapted from Hurley (2006)). A = horizontal entrance diameter or width, B = vertical entrance diameter, C = cavity depth to nest chamber floor, D = maximum diameter of nest chamber floor, E = minimum diameter of nest chamber floor and F = nest chamber wall thickness...... 11 Figure 6. Counts of nest sites known to be used by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri) at Pine Plains, Wyperfeld National Park from 1995 to 2008.  = Annual count of nest trees remaining.  = count of remaining nest trees (March 2014).  = Count of nest trees including simulated natural cavities (May 2014). Black trend line = linear regression, R2 = 0.894. Orange line = linear regression following the inclusion of simulated natural cavities, R2 = 0.822...... 13 Figure 7. Diameter at breast height (DBH) of Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range...... 16 Figure 8. Height of cavity entrance above ground in Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range...... 16 Figure 9. Width (horizontal diameter) of cavity entrance in Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range...... 16 Figure 10. Height (vertical diameter) of cavity entrance in Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range. . 16 Figure 11. Cavity depth from entrance to nest chamber floor in Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range...... 17 Figure 12. Average diameter of nest chamber floor in Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range...... 17 Figure 13. Average thickness of nest chamber walls in Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range...... 17

List of tables

Table 1. Dimensions of naturally occurring Callitris cavities used by Major Mitchell’s Cockatoo breeding in Pine Plains (n = 55). The ‘Key’ values relate to the labels in Figure 4. Listed are the median, mean and the standard deviation (SD) of the mean. Adapted from Hurley (2006)...... 11 Table 2. Cavity features measured in Slender Cypress Pine tree cavities and statistics (range, median, mean ± standard deviation, sample size and the percentage of live trees) for each method of nest cavity creation from those excavated, augmented, restored or nest-box averaged for all simulated cavities combined (n = 27)...... 12 Table 3. Comparison of Simulated Natural Cavity production processes. Listed are the advantages and restrictions in the application of each process and the estimated longevity of each process...... 14

Comparing simulated natural cavities to natural cavities in Callitris

Executive Summary

Introduction The availability of tree cavities is a limiting resource for a range of Victorian fauna (Gibbons & Lindenmayer, 2002; Manning et al., 2013; Saunders et al., 2014). As a result, loss of hollow bearing trees has been listed as a threatening process under the Flora and Fauna Guarantee Act 1988 (FFG Act). This project addresses the shortage of tree cavities available for use by the FFG Act listed Major Mitchell’s Cockatoo (MMC) (Lophochroa leadbeateri leadbeateri) for nesting and night roosting (Hurley, 2006). The project was funded by the Victorian Environmental Partnerships Program (VEPP) in 2013-15. Tree cavity availability for fauna is an issue in north-west Victoria because 79.6% of semi-arid woodlands in Victoria having been cleared since European settlement. Consequently, these are amongst the most threatened of woodland vegetation communities in Victoria (Olsen et al., 2005). In addition, they are a significant component of the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 listed Pine, Buloke woodlands of the Riverina vegetation community. The 7,700 ha area of Wyperfeld National Park referred to as ‘Pine Plains’ is the focal area for this project. It represents the largest extent of Slender Cypress Pine (Callitris gracilis murrayensis) (henceforth Callitris) dominated semi-arid woodland in Victoria and contains Victoria’s largest breeding colony of the Flora and Fauna Guarantee Act 1988 listed Major Mitchell’s Cockatoo (MMC) (Gowans & Gibson, 2005; Hurley & Cheers, 2012; Kenny et al., 2012). MMC at Pine Plains specialise in nesting exclusively in Callitris (Hurley, 2009). Due to a long history of logging and stock and kangaroo (Macropus Spp.) grazing and browsing by European Rabbits (Oryctolagus cuniculus), there has been very little successful regeneration of Callitris since the 1850s (Durham, 2001; Sandell, 2011). Long-term monitoring of 63 MMC nests between 1995 to 2013 has predicted that this critical resource will be gone by 2024 (Hurley, 2011). The lack of recruitment of large cavity-bearing trees places a high priority on short and medium term actions to address this shortage of cavities. The Lake Albacutya-Wyperfeld Bush Fire (February 2014) accelerated this loss with 92% of cavity bearing trees lost within the 4,957ha burnt in Plains. This tree cavity project represents an enhancement of previous techniques to create nest cavities for MMC’s that have greater long-term efficacy than traditional nest boxes (Hurley, 2009).

Project Objectives/Outcomes There were three primary objectives/outcomes to this study: 1. develop field techniques to form cavities in Callitris to simulate natural cavities used by Major Mitchell’s Cockatoo; 1. create 25 cavities to simulate natural cavities prior to the 2014 spring breeding season; 2. statistically compare the dimensions of these with a set of natural cavities; and 3. provide a report describing and illustrating techniques developed to form simulated natural cavities in Callitris. The processes for cavity formation developed in this project were grouped into five distinct categories depending upon the developmental stage (i.e. age) of the tree and the condition or existence of any cavity within the tree. Namely: excavate, augment, restore, initiate and nest-box.

Conclusion This project has developed some innovative techniques for simulating natural cavities in Callitris tree trunks (Figure 1). Thus old cavities fallen into disrepair can be restored, new cavities can be excavated from solid heartwood and trees with scars or decay in the early stages of cavity formation can be initiated or augmented to accelerate the cavity formation process. This allows for cavity formation techniques to be applied to the widest array of standing trees. Quantifying the success of this project is dependent upon monitoring occupancy by MMCs of Callitris cavities (both natural and SNC) in Spring 2014. Early observations made during the April 2014 look promising - as the elevated work platform was being lowered from a newly excavated cavity, a MMC pair flew up to the

Comparing simulated natural cavities to natural cavities in Callitris

4 entrance and immediately began inspecting the cavity. Observations made on three successive trips detected a MMC pair occupying this same cavity.

Recommendations

1. Conduct annual spring monitoring of all cavities at Pine Plains to determine the uptake and breeding success associated with the SNC to be compared with natural cavities for at least the next three years.

2. Conduct long term monitoring of tree health indicators such as canopy density to determine any impacts of this technique on live treated trees.

3. Evaluate the efficacy of creating SNC’s versus the use of Nest Boxes in terms of both long-term use and costs to maintain/create.

4. Expand the construction and installation of nest-boxes to replace all cavities lost during the 2014 bushfires.

5. Develop a management plan for Slender Cypress Pine in Victoria to ensure adequate recruitment of trees capable of forming suitable cavities and continued retention of mature trees.

Comparing simulated natural cavities to natural cavities in Callitris

Introduction

Cavities in large trees provide critical ecological functions in forests worldwide. In Australia cavities provide vital nesting and roosting/denning resources for 303 cavity-using vertebrate species, or around 15% of all terrestrial vertebrate species (Gibbons & Lindenmayer, 2002). These cavities can be formed by various factors either alone or in combination. Most notable of these factors are wind damage, fire, fungi and bacteria and excavation by vertebrates. Natural cavity formation can commence from a young age, however, the age at which trees contain cavities suitable for occupancy by vertebrate fauna may be considerably older. A review of cavity formation in Australian Eucalypts recorded hollow formation in trees 35 years old with large cavities remaining rare until trees are >220 years old (Gibbons & Lindenmayer, 2002) Cavity-dependent fauna can be either primary occupiers (or excavators) or secondary cavity occupiers (Newton, 1994). In Australia there are no vertebrate fauna that excavate cavities to the extent that northern hemisphere woodpeckers do (Cockle et al., 2011). Many ecosystems are experiencing long-term loss of large trees and their cavities or a failure to recruit new large trees or both (Fischer et al., 2010; Parnaby et al., 2010; Lindenmayer et al., 2014). Overcoming the loss of large cavity bearing trees has traditionally involved the installation of nest-boxes. (Libois et al., 2012; Brazill-Boast et al., 2013). However, cost-benefit analyses of supplying nest boxes for threatened species has suggested that this action is controversial when applied on a meaningful scale for endangered species (Caughley, 1994; Spring et al., 2001; Lindenmayer et al., 2002; Harley & Spring, 2003). Excavating cavities in trees to simulate natural cavities has not been widely considered in these debates. Repair of damaged tree cavities has however been implemented for Carnaby’s Black-cockatoo (Calyptorhynchus latirostris) in Western Australia and for Glossy Black Cockatoos (Calyptorhynchus lathami halmaturinus) on Kangaroo Island in South Australia (Goldingay & Stevens, 2009; Garnett et al., 2011; Saunders et al., 2014). As a conservation technique excavation of cavities has similar initial costs to the building and installation of nest boxes but promises to be more durable with less frequent (if any) maintenance action required. Thus, it is anticipated that simulated natural cavities (SNC) will have reduced costs over the lifetime of each cavity compared to nest boxes. As such, it is a novel approach that warrants field testing. This report details several techniques developed to create SNC in standing Slender Cypress Pine (Callitris gracilis murrayensis) (or simply Callitris) at Pine Plains in Wyperfeld National Park. The creation of tree cavities in this project addresses a high priority action listed in the Department of Environment and Primary Industries’ (DEPI) Action for Biodiversity Conservation (ABC) database for implementation in 2014 and was funded by the Victorian Environmental Partnerships Program (VEPP) in 2013-15. These SNC are designed for use by the Flora and Fauna Guarantee Act 1988 listed Major Mitchell’s Cockatoo (MMC) (Lophochroa leadbeateri leadbeateri) for nesting and night roosting (Hurley, 2006).

Background Semi-arid woodlands are treed vegetation communities characterised by an overstorey dominated by non- eucalypt tree species. Characteristic over-story species are Callitris, Buloke (Allocasuarina luehmannii) and Belah (Casuarina pauper). Tree cavity availability for fauna is an issue in north-west Victoria due to 79.6% of semi-arid woodlands in Victoria having been cleared since European settlement (Cheal et al., 2011). Consequently, these are amongst the most threatened of woodland vegetation communities in Victoria (Olsen et al., 2005). In addition, they are a significant component of the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 listed Pine, Buloke woodlands of the Riverina vegetation community. While Callitris form cavities from 80 years of age, the average sized cavities for nesting by the Flora and Fauna Guarantee Act 1988 listed Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeaterii) do not occur until the trees are 170 years old (Gibson et al., 2008). Pine Plains contains an area of 4,974 Ha of semi-arid woodland and grasslands of which 2,194 Ha is dominated by Callitris which considered critically important to the conservation of MMC (Durham, 2001; Gowans & Gibson, 2005). This was cited as one of the prime reasons for the incorporation of Pine Plains into the Wyperfeld National Park (LCC, 1989). More recently, a spring 2011 survey for breeding MMC breeding pairs in 28 remnant semi-arid woodland reserves across the Victorian Mallee confirmed that Pine Plains contains the largest breeding group of MMC in Victoria (Hurley & Cheers, 2012). In that survey a total of three pairs of MMC were recorded across the 28 reserves while 29 MMC pairs were recorded breeding within Pine Plains alone.

Comparing simulated natural cavities to natural cavities in Callitris

Pine Plains has experienced a long history of Callitris timber harvesting as well as overgrazing, initially by stock and then by rabbits, kangaroos and feral goats since its incorporation into Wyperfeld NP in 1996 (Durham, 2001; Sandell, 2011). As a consequence. there has been very little successful regeneration of Callitris since the 1850s. Conversely, the rate of loss of large old cavity bearing Callitris at Pine Plains has been monitored from 1995 to 2013. Starting with 63 Callitris used for nesting by MMC in 1995 the status (standing or not) of each was recorded annually (Figure 2). Loss of these large cavity bearing Callitris was primarily attributed to tree collapse as a result of internal decay of dead trees and was accelerated by storm and bushfire events. In January 2014, the Lake Albacutya-Wyperfeld bushfire burnt an extensive area of 4,957 Ha (63.8%) of the remnant Callitris dominated semi-arid woodlands. This event further reduced the studied cohort of nesting cavities in Pine Plains to 13. This is a decline of 92% from the 1995 nest numbers, equating to a loss of 2.6 trees per annum or 4.2% per annum. Without significant intervention over the short to medium term, the original cohort of Callitris tree cavities suitable for use by MMC are projected to be gone by 2024 (Figure 2). With this prediction and in response to the increasing concerns regarding the loss of cavity-bearing trees, it was decided to take immediate action to supplement large tree cavities (Manning et al., 2013) at Pine Plains. While this project was planned prior to the January 2014 bushfire, it is now viewed as a critical conservation action following the impacts of that fire.

Count of known nest trees nest of known Count 20

0 1990 1995 2000 2005 2010 2015 2020 2025 2030 Year

Figure 2. Counts of nest sites used by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri) at Pine Plains, Wyperfeld National Park from 1995 to 2014.  = Annual count of nest trees remaining.  = count of remaining nest trees (March 2014). Black trend line = linear regression, R2 = 0.894. The novel technique of excavating cavities in trees to create SNC has not been previously undertaken on such a scale in Callitris. The dimensions of the SNC constructed at Pine Plains were based on the median dimensions of measurements taken from 55 natural cavities used for breeding by MMC (Hurley, 2006). The feasibility of some of the techniques applied here were initially trialled on 12 Callitris at Pine Plains in 2009 (Hurley, 2009). This report is intended to provide an assessment of how closely the SNCs mimicked the physical dimensions of natural cavities. A separate manual has been created as an illustrated guide for use by field practitioners wishing to undertaken similar conservation actions.

Comparing simulated natural cavities to natural cavities in Callitris

Project Objectives There were three primary objectives to this study: 2. develop field techniques to form cavities in Callitris to simulate natural cavities used by Major Mitchell’s Cockatoo; 3. create 25 cavities to simulate natural cavities prior to the 2014 spring breeding season; 4. statistically compare the dimensions of these with a set of natural cavities; and 5. provide a report describing and illustrating techniques developed to form simulated natural cavities in Callitris.

Methods

This methods section provides a summary of the following components of the techniques used to create simulated natural cavities:  definition of key terms;  conceptual model of temporal application of each SNC technique to Callitris;  description of tree selection process;  decision matrix to guide SNC technique selection; and  summary of the dimensions of natural cavities used by MMC for nesting in Pine Plains. A more detailed description of the methods used in the generation of simulated natural cavities is provided in the accompanying manual “Techniques for creating simulated natural cavities in Callitris“ (Hurley & Harris, In draft - 2014).

Definitions Simulated Natural Cavity (SNC) is a collective term applied to cavities developed in this project via more than one process. These can be grouped into five distinct process categories depending upon the developmental stage (i.e. age) and health of the tree and the condition or existence of any cavity within the tree:

Excavate: Create entrance and new cavity by carving out heartwood in a standing tree.

Augment: Accelerate natural processes through the removal of decayed material and heartwood to produce a secure cavity. Augmentation works may include enlarging entrance and cavity dimensions or modifying nest entrance to protect from rainwater run-off.

Restore: Reinstate old degraded cavities through the re-establishment of nest chamber floor and covering of large cracks to secure cavity walls.

Nest-box: Construction of a nest-box made from a single salvaged Callitris log by excavation of heart wood and carving an entrance to mimic a natural cavity for nesting. Mounting, in a tree, a nest- box in a position considered suitable to Major Mitchell’s Cockatoo.

Initiate: Removing a branch or creating a scar to expose heartwood, to initiate/accelerate natural cavity formation.

This last action is intended to encourage natural processes to complete cavity formation. It is undertaken by branch removal or scar creation so as to expose the heartwood. Freshly exposed heartwood is very pale compared to the grey of the outer bark layer. This contrast forms a strong visual stimulus that attracts large cockatoo species such as Galahs and MMC to start excavating an entrance and cavity. This technique was considered but not acted upon during this study.

Comparing simulated natural cavities to natural cavities in Callitris

SNC technique Vs tree growth stage SNC techniques aim to provide robust cavities which replicate the physical and thermal characteristics of cavities known to have provided breeding success for MMC at Pine Plains. Each of these techniques can be temporally located within a conceptual model of tree development and cavity formation (Figure 3).

Figure 3. Conceptual time line of tree growth and appropriate growth stages for SNC intervention. Letters represent the location of SNC techniques in the temporal sequence of large old tree development and loss. I = Initiate, E = Excavation, A = Augmentation and R = Restoration.

Tree selection In March 2014, a survey of the Lake Albacutya-Wyperfeld fire impacted areas of Pine Plains and surrounding woodland was undertaken to identify standing live and dead trees of a size capable of bearing cavities suitable for MMC use. Data on tree dimension diameter at breast height (DBH), structure, health and growth form were recorded along with additional information about existing cavities or wounds with exposed heartwood. The site selection of candidate trees for SNC works targeted trees of DBH ≥ 50 cm and a trunk height of ≥ 8 m (Hurley, 2006). Consideration was also given to the proximity of other candidate trees and any existing cavity-bearing trees. The average distance between active MMC nests was found to be 400 m and the minimum recorded distance was 50 m (n = 63) (Hurley unpublished data 2001). However, following the 2014 bushfire (when ~92% of the known cavity-bearing trees were destroyed) the number of candidate trees within the area of the fire scar was very limited and so the proximity criterion was relaxed. Therefore, if two or more candidate trees were identified < 50 m apart the larger or more stable tree was selected. Where possible, candidate trees were located in areas where nest trees had previously been known to occur in order to offer a replacement cavity within the breeding territory. Also preference was given to sites assessed to have low human visitation rates. If suitable candidate trees, in such areas could not be found, GPS coordinates were collected for trees that could potentially support a nest-box made from the trunk of a fallen Callitris. Criteria were developed for selecting the most appropriate SNC technique. This lead to the formation of a decision matrix to provide clarity in SNC technique selection (Figure 4). SNC techniques may be applied to both live or dead standing Callitris as the status (live or dead) of the Callitris appears not to deter MMC breeding. Only 14.3% of Callitris used by MMC in the spring of 2010 were alive in contrast to the 54% alive in 2006 (Hurley, 2011).

Comparing simulated natural cavities to natural cavities in Callitris

Figure 4. Decision matrix for the selection of the appropriate technique in simulated cavity formation in Slender Callitris Pine (Callitris gracilis murrayensis). Diamonds are decision points and light orange boxes are actions. The orange strips represent recording and monitoring activities. The pale orange rectangles represent actions or SNC techniques.

Comparing simulated natural cavities to natural cavities in Callitris

Cavity dimensions The dimensions and shape of the cavities to be created are shown in Figure 5. These comprise an entrance of 13 cm wide (A) and ~22 cm tall (B) in the side of a trunk. The bottom lip of the entrance should be at least 60 cm (C) above the nest chamber floor, which should in turn be ~19 cm (D) x 19 cm (E) in diameter (Figure 5). The actual dimensions applied to each SNC are summarised in Table 1.

A B

C F E D

Figure 5. Measurements of naturally occurring Major Mitchell’s Cockatoo nest cavities in Callitris tree trunks (n = 55) (figure adapted from Hurley (2006)). A = horizontal entrance diameter or width, B = vertical entrance diameter, C = cavity depth to nest chamber floor, D = maximum diameter of nest chamber floor, E = minimum diameter of nest chamber floor and F = nest chamber wall thickness.

Tree DBH was measured at 1.4 m above ground level using a diameter tape measure. Wall thickness was calculated by measuring the diameter of the trunk at the level of the nest chamber floor, then subtracting from this the average of two internal diameters of the nest chamber floor. This figure was then halved to give the average thickness of the nest chamber wall.

Cavity dimensions Key Range Median Mean SD Tree DBH N/A* 34-149 69.5 72.5 ± 24.5 Entrance – Horizontal diameter (cm) A 8-30 13 13.3 ± 4.1 Entrance – Vertical diameter (cm) B 9-80 22 27.6 ± 13.7

Depth to nest chamber floor(cm) C 19-180 51 53.9 ± 25.8 Nest chamber floor diameter (cm) D 9-34 19 18.0 ± 4.1 Nest chamber wall thickness (cm) F 6-20 9 10.1 ± 4.0 *Tree DBH not illustrated in Figure 5. #Calculation for nest chamber floor area describe in text above.

Comparing simulated natural cavities to natural cavities in Callitris

Results

Between April and May 2014 a total of 27 SNC were generated in as many Callitris trees over 15 field days. During this period, 10 SNC were excavated, 11 augmented, four restored and two nest-boxes were made, one nest-box installed in a Casuarina second nest box has been built, its installation remains pending. Construction times varied depending upon the SNC process being undertaken. As a guide it takes, on average, two people four hours to generate a single SNC in a Callitris. Whereas, it took two people, a full day for the construction, plus half a day for the installation, of a single nest-box from a salvaged Callitris log. In all of these situations, two experienced arboriculturalists were required and on occasion additional field staff were used in support roles. A full range of measurements were taken from the SNCs formed and the summary statistics are listed in Table 2.

Table 2. Cavity features measured in Slender Cypress Pine tree cavities and statistics (range, median, mean ± standard deviation, sample size and the percentage of live trees) for each method of nest cavity creation from those excavated, augmented, restored or nest-box averaged for all simulated cavities combined (n = 27).

Nest cavity type Cavity feature Nest-box Excavated Augmented Restored Combined SNC 40 – 53, 50 54 – 76, 63 77 – 140, 85.5 40 – 140, 56 N/A Tree DBH (cm) 48.4 ± 4.3, 10 64.6 ± 8.0, 11 97 ± 29.1, 4 63.3 ± 20.5, 25 5 – 12, 6.0 4 – 14, 7.0 6 – 8, 6.5 4 – 14, 6.0 Entrance – height above ground (m) 8 6.7 ± 2.2, 10 8.5 ± 3.5, 11 6.8 ± 1.0, 4 7.5 ± 2.8, 25 12 – 20, 13 12 – 30, 14 13 - 18, 14 12 – 30, 14.0 Entrance – diameter horizontal (cm) 13 14.4 ± 2.8, 10 15. 5 ± 5.1, 11 14.8 ± 2.4, 4 14.9 ± 3.8, 25 20 – 60, 30.0 14 – 40, 28 18 -54, 30 14 – 60, 30.0 Entrance – diameter vertical (cm) 22 32.3 ± 12.2, 10 26.4 ±7.4, 11 33 ± 17.2, 4 29.8 ± 11.18, 25 42 – 110, 73.5 50 – 89, 64 51 – 68, 64 42 -110, 68 Depth to nest floor (cm)** 70 75.7 ± 20.4, 10 65.7 ±12.2, 11 61.8 ± 8.1, 4 69.1 ± 16.1, 25 13 – 26, 20.5 16 – 30, 22 20 – 22, 22.0 13 – 30, 21 Nest– floor diameter (cm)** 20 20.3 ± 3.5.2, 10 21.5 ± 3.6, 11 21.3 ± 1.0, 4 21 ± 3.2, 25 5 – 20, 8.5 5 – 15.5, 7.0 4 – 21.5, 11.5 4 – 21.5, 8.5 Cavity – wall thickness (cm)** 10 11 ±5.5, 10 8.9 ± 3.5, 11 12.13 ± 7.6, 4 10.3 ± 5.0, 25

Number of cavities, % live trees 1, 100% 10, 60% 11, 27.3% 4, 0% 27, 36%

*Nest-box dimensions are for the one nest-box installed in a Casuarina. **T-test recorded a significant difference between the means of the combined SNC to the natural cavities (Table 1).

Statistics The DBH of natural cavity-bearing trees used by MMCs are larger, but not significantly so, compared to trees with SNCs (t(1,78) = -1.67, P = 0.1; natural DBH = 72.5 ± 24.5 cm; SNC DBH = 63.3 ± 20.5 cm; mean±SD). The dimensions of SNCs, in general, resembled the dimensions of naturally occurring cavities in Callitris used by MMC at Pine Plains. Entrance diameters (horizontal) (t(1,72) = -1.755, P = 0.085) and entrance diameters (vertical) (t(1,77) = -0.647, P = 0.52) of both sets of cavities were not significantly different. The height of the SNC entrances above ground were not different from the natural cavities (t(1,58) = -0.982, P = 0.332). The depth from cavity entrance to chamber floor of SNCs were deeper than natural cavities (t(1,68) = 3.309, P = 0.001; SNC(ave) = 69 ± 16.1 cm; natural(ave) = 53 ± 26.2 cm; mean±SD). The average nest chamber floor diameter of SNCs were larger than those recorded in natural cavities (t(1,73) =-2.27, P =0.026; SNC(ave) = 21 ± 3.2 cm; natural(ave) = 19 ± 4.2 cm; mean±SD). Whereas, the wall thickness of SNC were significantly thinner than natural cavities (t(1,76) = -2.829, P = 0.006; SNC(ave) = 10.3 ± 5 cm; natural(ave) = 14.1 ± 5.3 cm; mean±SD). Box plots of natural vs SNC comparing tree and cavity measurements further illustrate the distribution of the data relating to each measurement (refer to Appendix I). The inclusion of these 25 SNCs has altered the regression line of known nest trees so as to increase the projected time span of cavity bearing tree retention at Pine Plains from 2024 until 2037 (Figure 6).

Comparing simulated natural cavities to natural cavities in Callitris

30 Count of known nest trees nest of known Count 20

0 1990 2000 2010 2020 2030 2040

Year

Figure 6. Counts of nest sites known to be used by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri) at Pine Plains, Wyperfeld National Park from 1995 to 2008.  = Annual count of nest trees remaining.  = count of remaining nest trees (March 2014).  = Count of nest trees including simulated natural cavities (May 2014). Black trend line = linear regression, R2 = 0.894. Orange line = linear regression following the inclusion of simulated natural cavities, R2 = 0.822.

Comparing simulated natural cavities to natural cavities in Callitris

Discussion

The primary objective of this study was to develop field techniques to form cavities in Callitris to simulate natural cavities used by Major Mitchell’s Cockatoo for breeding. Within the Pine Plains area MMC are particularly selective in their choice of nesting cavity, balancing a range of factors such as ease of acquisition, nest chamber dimensions, thermal properties, risk of flooding or tree collapse, predation risk and competition in comparison to sympatric and other Psittaciformes (Rowley & Chapman, 1991; Hurley, 2006; Renton & Brightsmith, 2009; Johnstone, 2013; Saunders et al., 2014). This project has been successful, at the proof of concept stage, in the development of and the application of field techniques to form simulated natural cavities with the formation of 25 SNCs that closely resemble dimensions of natural cavities in Callitris in Pine Plains. Having developed and applied SNC formation techniques, the second objective of this study was to describe these in such a way so that they could be used by other workers in the field. An illustrated description of the techniques grouped by process involved in the formation of the various SNCs has been prepared as a practical guide for others to undertake similar conservation works (Hurley & Harris, In draft - 2014). To form SNCs different approaches are required depending on the state of the tree and the stage of any existing cavities (i.e. incipient or decayed). Grouping the formation of SNCs into distinct categories, each with their advantages and restrictions in formation (Table 3), provides a decision matrix by which to select the most appropriate cavity formation process. This allows trees that might otherwise not be considered candidates for cavity excavation to still be considered for another SNC process. Thus the diversity of SNC processes allows more standing Callitris trees to be considered for SNC formation. The publishing of SNC measurements also addresses concerns raised by a general lack of reporting of this information in breeding studies involving nest-boxes (Lambrechts et al., 2012). It would be beneficial to MMC conservation more broadly if the SNC techniques developed in this project were to be applied to other reserves with suitably large (DBH ≥ 50 cm) Callitris across the Victorian mallee (Hurley & Cheers, 2012).

Table 3. Comparison of Simulated Natural Cavity production processes. Listed are the advantages and restrictions in the application of each process and the estimated longevity of each process.

Cavity formation Estimated Advantages Restrictions process longevity Easy access to heartwood reduces excavation Technique restricted to dead trees and snags of living time. trees Excavate > 30 Years Crown can be heavily weight reduced to Access generally restricted to EWP. increase stability of trunk. On live, healthy trees can be undertaken with Access to heartwood is limited to cavity entrance rope access techniques allowing installation increasing excavation time. Augment > 30 Years on steep slopes that are too restrictive for an Risk of damage to sapwood, which if occurs may EWP negatively impact tree health. Excavation of detritus and debris is rapid in Technique is associated with dead trees and those in Restore > 5 Years comparison to heartwood excavation. advanced senescence, largely restricting access to EWP Encourages natural processes to begin cavity Potentially, very slow to form suitable cavities. formation. Initiate > 30 years Less obvious, so less attractive to human disturbance. Can be placed in trees not large enough to Obligatory annual maintenance checks. Nest-box ~ 10 Years cater for suitably large enough cavity. Easily detected and attractive to human disturbance.

Spring monitoring will determine the uptake of the SNCs by the target species. This monitoring must include some measurement of breeding success and not just spring season occupancy. Because, nest-boxes installed for several species have been found to be very attractive to the target species but have ended up acting as an ecological sink for example Barn Owls (Tyto alba) (Klein et al., 2007) and American Kestrels (Falco sparverius) (Strasser & Heath, 2013). An ecological sink is an attractive habitat or nest site which is occupied but does not provide for successful breeding by the residents (Delibes et al., 2001). Hence, monitoring breeding success will allow comparisons between individual SNCs and processes with existing natural cavities to determine differences over time.

Comparing simulated natural cavities to natural cavities in Callitris

Longer term monitoring of SNCs in tree trunks and nest-boxes will inform land managers of the maintenance costs and effective durability of each method (Groom, 2010). While the use of nest-boxes (or SNCs) has caused controversy among conservation biologists, this project illustrates a feasible and practical application of the concept in circumstances where natural processes are failing to keep pace with the loss of nest cavities for a cavity dependent threatened species (Lindenmayer et al., 1991; Spring et al., 2001; Lindenmayer et al., 2002; Harley & Spring, 2003; Lindenmayer et al., 2009). On-going monitoring of the SNCs and nest-boxes at Pine Plains represents a rare opportunity in Australian wildlife conservation to undertake a const-benefit analysis between SNCs and nest-boxes over time. The projected loss of cavity bearing Callitris means the nest-box design and construction techniques illustrated will become essential for providing potentially all future nesting cavities for MMC at Pine Plains until a new cohort of Callitris are large enough to form cavities naturally (Gibbons et al., 2008). This cohort will be from those Callitris germinated in 1996 following the temporary collapse of rabbit populations following the release of Rabbit Haemorrhagic Disease that year (Sandell, 2011). However, new cavities amongst this cohort of trees will not start to become available until 2076 (62 years from now). In the meantime, the existing cavity bearing trees are predicted to be gone by 2037 (Figure 6). Implementation of other actions to retain the remaining large old trains is an urgent conservation priority for these Callitris woodlands. Failing this, it is almost certain that the breeding of MMC will depend upon SNCs and then nest-boxes at Pine Plains long before 2076. This leaves a gap of at least 39 years in which there will be no, or very few, Callitris large enough to support either a natural cavity or a SNC. Over this period the installation of nest-boxes on other tree species or alternative structures will be necessary to support the breeding of MMC in Pine Plains. In this time the conservation status of MMC will move into the IUCN category of “conservation dependent” to reflect this dependence upon these artificially generated cavities (Garnett et al., 2011).

Recommendations

2. Conduct long term monitoring of tree health indicators such as canopy density to determine any impacts of this technique on live treated trees.

3. Evaluate the efficacy of creating SNC’s versus the use of Nest Boxes in terms of both long-term use and costs to maintain/create.

4. Expand the construction and installation of nest-boxes to replace all cavities lost during the 2014 bushfires.

5. Develop a management plan for Slender Cypress Pine in Victoria to ensure adequate recruitment of trees capable of forming suitable cavities and continued retention of mature trees.

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Comparing simulated natural cavities to natural cavities in Callitris

Appendix I

Box plots of tree and cavity measurements

160 16

120 12

80 8 Tree DBHTree (cm)

40 4 Entranceaboveground (cm)

0 0 Natural Simulated Natural Simulated Cavity Origin Cavity Origin

Figure 7. Diameter at breast height (DBH) of Callitris Figure 8. Height of cavity entrance above ground in trees with natural (n = 55) and simulated cavities (n = 25). Callitris trees with natural (n = 55) and simulated cavities (n = Mean is the dark line, grey boxes are the 1st and 3rd quartiles 25). Mean is the dark line, grey boxes are the 1st and 3rd and the whiskers are the range. quartiles and the whiskers are the range.

40 100

30 75

20 50

Entrance - Vertical diameter (cm) diameter Vertical Entrance- Entrance horizontal diameter (cm) diameter horizontal Entrance 0 0 Natural Simulated Natural Simulated Cavity origin Cavity origin

Figure 9. Width (horizontal diameter) of cavity entrance in Figure 10. Height (vertical diameter) of cavity entrance in Callitris trees with natural (n = 55) and simulated cavities (n = Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range. quartiles and the whiskers are the range.

Comparing simulated natural cavities to natural cavities in Callitris

200 40

150 30

100 20 Cavity Depth(cm) Cavity

50 10 Nest floor diameter (ave.) (cm) (ave.) diameter floor Nest

0 0 Natural Simulated Natural Simulated Cavity origin Cavity origin

Figure 11. Cavity depth from entrance to nest chamber Figure 12. Average diameter of nest chamber floor in floor in Callitris trees with natural (n = 55) and simulated Callitris trees with natural (n = 55) and simulated cavities (n = cavities (n = 25). Mean is the dark line, grey boxes are the 1st 25). Mean is the dark line, grey boxes are the 1st and 3rd and 3rd quartiles and the whiskers are the range. quartiles and the whiskers are the range.

5 Cavity wall thickness (cm) thickness wall Cavity

0 Natural Simulated Cavity origin

Figure 13. Average thickness of nest chamber walls in Callitris trees with natural (n = 55) and simulated cavities (n = 25). Mean is the dark line, grey boxes are the 1st and 3rd quartiles and the whiskers are the range.

Comparing simulated natural cavities to natural cavities in Callitris

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Comparing simulated natural cavities to natural cavities in Callitris