Corresponding author: Denis A. Saunders (
Academic editor: Klaus Henle
Nature conservation and agricultural production may be considered as conflicting objectives, but for a wheat and sheep property in Western Australia they have been pivotal management objectives for the last 48 years. Koobabbie, a 7,173 ha property, has retained 41.5% of the original native vegetation, and is a designated Important Bird Area by BirdLife Australia, while still being an economically profitable agricultural enterprise. Since 1987 the owners of Koobabbie have kept detailed records of the avifauna of the property, and encouraged staff from government, non-government and academic organisations to conduct research and monitoring of the endangered Carnaby’s Cockatoo
Saunders DA, Dawson R, Doley A, Lauri J, Le Souëf A, Mawson PR, Warren K, White N (2014) Nature conservation on agricultural land: a case study of the endangered Carnaby’s Cockatoo
This paper is dedicated to the late John Doley (1937–2007), whose wise counsel and hard work contributed greatly to the Carnaby’s Cockatoo conservation program on Koobabbie.
Changes in land use and habitat conversion pose the greatest threats to biodiversity throughout the world. Agricultural intensification is one of the major threats (
Throughout the world’s agricultural zones, nature conservation and intensive agricultural production may be considered as conflicting objectives, but for one wheat and sheep property called Koobabbie in the Waddy Forest district in the northern wheatbelt of Western Australia (WA) (
Koobabbie was not cleared of native vegetation when taken up by Alison Doley’s grandparents in 1906. Since then it has been developed as an economically profitable agricultural enterprise by three generations of the same family. In 1966, Alison and John, her late husband, took over management of Koobabbie. Their management objective was ecological and economic sustainability (
Between May 1987 and the end of 1990, the Doleys took part in CSIRO Division of Wildlife and Rangelands Research’s atlas of birds in the WA wheatbelt project (
In the early and mid-1980s, concern was raised about the impacts of clearing of native vegetation on the distribution, abundance, and breeding success of Carnaby’s Cockatoo (
Since then, staff, volunteers and students, variously from Birds Australia (now BirdLife Australia), WA Department of Conservation and Land Management (now Department of Parks and Wildlife), Perth Zoo, and Murdoch University have worked on aspects of the ecology, genetics and health of Carnaby’s Cockatoo on Koobabbie, as well as carrying out repairs to tree hollows used by the cockatoos, and installing artificial hollows. In addition, land care groups carried out revegetation projects to aid recovery of the species in the district. Although the various research activities and observations of Carnaby’s Cockatoo on Koobabbie were not coordinated and, to some extent, have been
This paper presents the results of the diverse research and monitoring activities conducted on Carnaby’s Cockatoo at Koobabbie. It demonstrates that valuable information can be extracted from data collected by volunteers and others on an
Koobabbie is located in the centre of the Northern Agricultural Catchment Council (NACC) area. It is an important area for the conservation of the avifauna of the NACC area (
Koobabbie has a Mediterranean climate of hot, dry summers and cool, wet winters. The property has a mean annual rainfall of 337 mm (1911–2011 rainfall records from Koobabbie) with 76% of the rainfall occurring between April and September. From 1987 to 2011, total annual rainfall varied from 198.6–560.4 mm. January is the hottest month with a mean daily maximum temperature 36.0 °C and minimum 18.5 °C (data from nearest temperature recording station at Carnamah, 39 km north-west of Koobabbie, Australian Bureau of Meteorology website
The property is 7,173 ha of which 41.5% still retains native vegetation, although 58% of this uncleared land is a major salt lake complex in the property’s northeast (Figure
Koobabbie showing property boundary, remnant vegetation, and revegetation 2007–2011).
Between 2007 and 2011, 164.6 ha of revegetation was carried out on Koobabbie (Figure
Detailed descriptions of Koobabbie and its management are provided in
Carnaby’s Cockatoo, a large black cockatoo with a distinctive white tail band, is endemic to southwestern Australia. It has been extensively studied (
From May 1987 to the present, the Doleys recorded every species of bird seen on Koobabbie each week. These data were presence only; for example, one Wedge-tailed Eagle (
From the breeding season of 2003, staff or volunteers from Birds Australia visited Koobabbie once each year, sometime from late September to early November, and searched for active Carnaby’s Cockatoo nests. This was done by looking in each hollow known by the Doleys to be used by Carnaby’s Cockatoo, or trees thought to contain a hollow of sufficient size to be suitable for the birds. Any trees with female Carnaby’s Cockatoo leaving the hollows or with nestlings or eggs were recorded for subsequent examination. This was carried out by staff from the Department of Conservation and Land Management who recorded the contents of the hollow. If nestlings were large enough to be handled (>3 weeks old), they were measured (length of folded left wing [mm] and body mass [g]), banded (Australian Bird and Bat Banding Scheme bands), and several breast feathers removed for genetic analyses.
The following dimensions were recorded from each hollow used by Carnaby’s Cockatoo: height of entrance above ground level (m); diameter of the entrance to the hollow (if circular or the width of the narrowest side, if not circular) (m); depth of the hollow (m); and diameter of the floor of the nest chamber (m). The species of tree providing the hollow was also noted.
Nestlings were aged by comparing the length of their folded left wing (mm) against a reference curve of the length of the folded left wing of known age nestlings from Coomallo Creek, using the method described by
Nestlings were sexed based on DNA analysis. DNA-based sex identification targeted the CHD-W and CHD-Z genes located on the sex chromosomes (female, ZW; male, ZZ) using modified primers of
Nearest neighbour analyses, using the distance between the waypoints function on
On 1 April 2004, seven artificial hollows were erected on Koobabbie. These hollows were constructed of sections of fallen hollow Salmon Gum, with a floor of metal covered with decayed heartwood material from fallen trees, a wooden roof, and an entrance opening to the top and side of the hollow. No measurements were taken of the internal dimensions of artificial hollows, but they were approximately 600–700 mm deep, with an internal diameter of at least 250 mm. They were supported on a 5.8 m length of 100 mm diameter galvanised water pipe. The pipe was supported on a galvanised iron bracket set in concrete with two bolts through the bracket and the pipe, so that by removing one bolt the pipe may be lowered using a front end loader or block and tackle should the hollow need repair. There were several constraints on placement of the artificial hollows; chance of use by Carnabys Cockatoo, vehicle access for erection, and clearance from neighbouring trees. All artificial hollows were erected in woodland known to be frequented by the cockatoos for nesting. Each hollow required access for a tractor with post-hole auger, an eight-tonne truck with 5.8 m of pole and hollow, and a front end loader with a loader bucket. The hollows were placed sufficiently far from neighbouring trees to ensure they would not be damaged should any of those trees fall. The artificial hollows were monitored during the same period natural hollows were monitored.
Galah and Western Corella compete for hollows with Carnaby’s Cockatoo, and in some cases destroy Carnaby’s Cockatoo eggs and take over hollows (
Feral Cats (
Carnaby’s Cockatoo is a regular breeding visitor to Koobabbie, arriving sometime between the first week in July and the third week in August (median arrival week the last week in July) (Table
Correlation between week of arrival of Carnaby’s Cockatoo at Koobabbie each year (1987–2013), and total autumn rainfall (March-May) each year at Badgingarra Research Station. Rainfall from this station has been used as the birds spend their non-breeding season on the coastal plain from Badgingarra northwards.
Week of arrival and departure of Carnaby’s Cockatoo at Koobabbie 1987–2013 and the length of time (number of weeks) the birds were on the property. Weeks are numbered from the first week in January with four weeks each month (i.e., 48 recording weeks in the year; for example week 25 is the first week in July).
Week # | 25 | 26 | 27 | 28 | 29 | 30 | 31 | ||||||
# years birds arrived | 1 | 4 | 7 | 6 | 6 | 2 | 1 | ||||||
Week # | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | |||
# years birds departed | 1 | 2 | 5 | 5 | 6 | 2 | 1 | 2 | 0 | 2 | |||
# weeks birds in area | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 |
# years | 1 | 1 | 4 | 3 | 3 | 4 | 3 | 3 | 0 | 2 | 0 | 0 | 1 |
The number of known breeding attempts by Carnaby’s Cockatoo at Koobabbie over the 11 years ranged from 18 when monitoring by Birds Australia commenced in 2003, to a maximum of 27 in 2008 (Figure
Number of known breeding attempts by Carnaby’s Cockatoo at Koobabbie 2003–2013 (diamonds). Known breeding attempts were established by examining the contents of the hollow. Number of female Carnaby’s Cockatoo flushed from tree hollows (squares), but the contents were not checked then, or were checked subsequently and no conclusive evidence of a nesting attempt was obtained.
The breeding population in 2009 was less than half that of 2008 due to the death of a number of females, and possibly males. On 30 September 2009, a male Carnaby’s Cockatoo was found dragging itself along the ground with its beak. It weighed 434 g, only two-thirds of the average body mass of adult males (
There was a similar episode in mid-October 2012, with five females found dead on eggs in their nest hollows. Again, a male with hind limb weakness was found on the ground near the homestead. It was sent for treatment at the Perth Zoo Veterinary Department, but later died. A female found in a moribund state in a nest hollow, was sent to the Perth Zoo Veterinary Department, and later euthanized. Carnaby’s Cockatoo feathers on the ground in a belt of woodland indicated an eighth bird had died. These losses again halved the breeding population such that only five breeding attempts were recorded in 2013 (Figure
Necropsies on the two birds found alive, but compromised in 2012, showed no signs of infectious disease or other significant pathological abnormalities, except for the female which had evidence of severe dehydration. Testing was negative for several infectious pathogens including Newcastle disease virus, avian influenza virus, beak and feather disease virus, avian polyomavirus,
During the period 2003–2013, the earliest that egg-laying commenced was Week 31 (Jul 31–Aug 6) in 2008, and the latest Week 45 (Nov 6–12) in 2009 (Table
Number of first eggs laid by week at Koobabbie 2003–2013. These data relate to the first egg laid in each clutch (clutches of two eggs are most common). No data are available for 2004.
Week | Dates | 2003 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | Total |
---|---|---|---|---|---|---|---|---|---|---|---|---|
31 | Jul 31–Aug 6 | 1 | 1 | |||||||||
32 | Aug 7–13 | |||||||||||
33 | Aug 14–20 | 2 | 1 | 3 | ||||||||
34 | Aug 21–27 | 2 | 1 | 1 | 4 | |||||||
35 | Aug 28–Sep 3 | 2 | 3 | 1 | 4 | 1 | 1 | 1 | 13 | |||
36 | Sep 4–10 | 1 | 2 | 4 | 1 | 1 | 2 | 1 | 12 | |||
37 | Sep 11–17 | 3 | 2 | 2 | 1 | 4 | 2 | 1 | 1 | 16 | ||
38 | Sep 18–24 | 2 | 2 | 2 | 3 | 9 | ||||||
39 | Sep 25–Oct 1 | 1 | 2 | 4 | 1 | 1 | 9 | |||||
40 | Oct 2–8 | 3 | 1 | 4 | ||||||||
41 | Oct 9–15 | 2 | 1 | 3 | ||||||||
42 | Oct 16–22 | 1 | 1 | |||||||||
43 | Oct 23–29 | 2 | 2 | |||||||||
44 | Oct 30–Nov 5 | |||||||||||
45 | Nov 6–12 | 1 | 1 | |||||||||
Total | 8 | 7 | 14 | 14 | 17 | 5 | 6 | 5 | 1 | 1 | 78 |
Maximum flock sizes recorded on the property were: 91 (November 1994); 40 (December 1998); 40–60 (December 1999); 58 (October 2001); 98 (November 2004); 46 (December 2007); 26 (September 2009); 18 (September 2010); 23 (November 2011); 18 (August 2012); and 11 or 12 (September 2013).
Carnaby’s Cockatoo were recorded feeding on Wild Radish (
DNA-based sex identification was carried out on 75 nestlings sampled from 2003–2010. Of these, 35 were identified as female and 40 as male (Table
Sex of nestlings at Koobabbie (2002–2010) as determined by DNA analysis.
Year | Females | Males | Total |
---|---|---|---|
2002 | 3 | 2 | 5 |
2003 | 5 | 4 | 9 |
2004 | 1 | 1 | 2 |
2005 | 2 | 4 | 6 |
2006 | 5 | 6 | 11 |
2007 | 4 | 13 | 17 |
2008 | 12 | 8 | 20 |
2009 | 1 | 0 | 1 |
2010 | 2 | 2 | 4 |
Total | 35 | 40 | 75 |
From the kinship analyses, fifteen breeding pairs were identified to have visited Koobabbie, at least twice, accounting for 48% of the offspring sample. Thirteen of these pairs were not recorded as breeding in consecutive years. Six pairs used the same tree at least twice.
Seventy-eight nestlings were measured and weighed at Koobabbie between 2003 and 2013 (Table
Number of nestlings measured at Koobabbie and the number of nestlings whose body mass was one standard deviation below the benchmark body mass (see text for details). The percentages are the proportion of the total nestlings measured that were more than one standard deviation (SD) below benchmark, and deemed to be in poor condition.
Year | # nestlings | # below -1 SD | % below 1 SD |
---|---|---|---|
2003 | 8 | 3 | 37.5% |
2005 | 7 | 0 | 0% |
2006 | 14 | 1 | 7.1% |
2007 | 14 | 3 | 21.4% |
2008 | 17 | 2 | 11.7% |
2009 | 5 | 3 | 60.0% |
2010 | 6 | 1 | 16.7% |
2011 | 5 | 0 | 0% |
2012 | 1 | 0 | 0% |
2013 | 1 | 0 | 0% |
Total | 78 | 13 | 16.7% |
Comparisons were made between data from Koobabbie and data from 963 nestlings at Coomallo Creek (1970–2013) and 73 from Manmanning (1969–1976). Of the Coomallo Creek nestlings, 110 (11.4%; annual range 0–28.6%) were more than one standard deviation below the benchmark body mass, and at Manmanning 46 (63.0%; 14.3–100%) of nestlings were more than one standard deviation below benchmark body mass.
There was a significant negative linear correlation (R² = 0.110; p = 0.004) between time after the commencement of egg-laying for the season and the percentage nestling body mass deviated from the benchmark (Figure
Significant correlation between the percentage of nestlings at Koobabbie whose body mass deviates from the benchmark body mass, and the time at which the egg from which they hatched was laid after the commencement of egg-laying for the season. Egg-laying commenced at Week 1.
Carnaby’s Cockatoo nested in hollows in 51 trees on Koobabbie, the dimensions of which are given in Table
Dimensions (m) of hollows used by Carnaby’s Cockatoo on Koobabbie 2003–2013.
Height (m) | Depth (m) | Entry Diameter (m) | Floor Diameter (m) | |
---|---|---|---|---|
Number | 51 | 49 | 49 | 49 |
Mean | 5.29 | 1.32 | 0.26 | 0.33 |
Median | 5.30 | 1.10 | 0.25 | 0.30 |
St Dev | 1.52 | 0.74 | 0.08 | 0.13 |
Range | 2.2–8.7 | 0.30–3.70 | 0.10–0.45 | 0.15–0.70 |
Of these hollows, 27 (52.9%) needed some form of repair, and three of the hollow-bearing trees (5.9%) had fallen over by the breeding season of 2013.
Between 2006 and 2008, the average distance between all hollow trees known to be used by Carnaby’s Cockatoo at Koobabbie varied from 130 to 180 m (Table
Average distance (km) to nearest neighbour of all hollow trees used by Carnaby’s Cockatoo at Koobabbie during 2006, 2007 and 2008. Also shown is the average distance between nearest neighbours of active hollows started in two-week periods in the same years (see text for details).
2006 | 2007 | 2008 | 2006–08 | |
---|---|---|---|---|
Average distance (km) between nearest neighbours of all active hollows | 0.18 ± 0.29 | 0.13 ± 0.16 | 0.15 ± 0.26 | 0.13 ± 0.24 |
Range | 0.03–1.23 | 0.03–0.79 | 0.03–1.13 | 0.03–1.2 |
Average distance (km) between nearest neighbour laid in a particular week or the previous week | 1.05 ± 1.02 | 1.04 ± 1.24 | 0.60 ± 0.76 | 0.86 ± 0.99 |
Range | 0.15–3.04 | 0.13–3.08 | 0.15–3.10 | 0.13–3.10 |
In 2004, the installation costs of each of the seven artificial hollows were $AUD225 for materials and $AUD330 for labour.
Six were used by Carnaby’s Cockatoo at least once over the period 2004 to 2013 (Table
Use of the seven artificial hollows installed on Koobabbie before the breeding season of 2004. CC = Carnaby’s Cockatoo: E = egg; F = female; N = nestling; RTBC = Red-tailed Black-Cockatoo; and dead refers to the fact that a dead Carnaby’s Cockatoo female was found in the hollow.
Nest No | 1.10.04 | 14.10.05 | 4.10.06 | 10.10.07 | 6.11.08 | 24.10.09 | 29.09.10 | 3.10.11 | 15.10.12 | 5.11.13 | Total |
---|---|---|---|---|---|---|---|---|---|---|---|
KART 1 | F CC | F CC | F CC | F CC | 4 | ||||||
KART 2 | F CC | F CC 2E | 2 CC E | F CC 1E | F CC 1E | Dead CC F 2E | 6 | ||||
KART 3 | Galah | Galah | Galah | Galah | Barn Owl | 0 | |||||
KART 4 | F CC | F CC 1N | F CC 1N1E | F CC 1N | 1 CC N | Dead CC F 1E | 1 CC N | F CC 2E | 8 | ||
KART 5 | F CC | F CC 1N1E | F CC 1E | F CC 1N | Galah | 1 CC N | RTBC | 5 | |||
KART 6 | Barn Owl | Galah | F CC 1N | Galah | 1 | ||||||
KART 7 | F CC | F CC 2E | F CC 1N | 1 CC N | Dead F CC | F CC | F CC | F CC 1E | 8 | ||
Total CC | 5 | 3 | 5 | 4 | 3 | 4 | 3 | 2 | 2 | 1 |
Eighty Carnaby’s Cockatoo nestlings were banded on Koobabbie between 2003 and 2013. It is not known how many of these fledged, or how many returned to breed. Two fledglings banded at Koobabbie were recorded outside their natal area. One young male was photographed in the Coomallo Creek breeding area on 12 November 2010 (
Of the six cockatoo species occurring on Koobabbie, Galah were the most common; then in decreasing order, Western Corella, Red-tailed Black-Cockatoo, Carnaby’s Cockatoo, Major Mitchell’s Cockatoo and Little Corella (Alison Doley
During September 1995, the Doleys recorded incidents in which Western Corella usurped Carnaby’s Cockatoo at five nest hollows known to be used by the latter. In one hollow three Western Corella eggs were removed from the hollow and Carnaby’s Cockatoo reclaimed the hollow, and laid two eggs. Subsequently a Western Corella was seen investigating the hollow, and the Doleys found both black cockatoo eggs had holes in the side consistent with them being pecked open. Between 8 February 1997 and 22 March 2014, 11,741 Galah and 4,591 Western Corella were shot on Koobabbie in the vicinity of known black cockatoo nesting hollows.
In October 2007, a female Carnaby’s Cockatoo was sitting on two eggs in a hollow in a dead Salmon Gum; this nesting attempt failed as the female was killed by a Cat. Thirty-eight Cats were shot on the property.
During the 2008 breeding season, Alison Doley found Carnaby’s Cockatoo nestlings in three hollows were being adversely affected by small black ants (species unknown). This constituted 11% of the hollows known to be used by Carnaby’s Cockatoo that season. Previous observations suggested that ants only invaded nest hollows in which there was a dead nestling. In Hollow 24 on 4 December 2008, the nestling was covered in ants and showing signs of distress. The cloaca and surrounding skin were reddened and scabby. The base of the tree in which the hollow was located was sprayed with chlorpyrifos. The ants were controlled, and by 15 December the nestling had recovered. It fledged on 15 January 2009. One other nestling was found affected by ants. The surrounds of the nest hollow were sprayed, and the nestling fledged on 19 February 2009. No other cases of attack by ants on nestlings were recorded.
Carnaby’s Cockatoo has been a regular breeding visitor to Koobabbie for as long as Alison Doley can remember.
It is difficult to establish a link between the numbers of Galah and Western Corella removed from the local populations, and the steady increase in nesting attempts by Carnaby’s Cockatoo. This is in part due to the fact that new nest hollows were still being located after 2005. Anecdotal evidence indicates that the program has been beneficial. For example, in the breeding season of 2007, a Carnaby’s Cockatoo commenced breeding in Artificial Hollow 7, but was usurped by a pair of Western Corella. The female Western Corella was shot. The next evening a female Carnaby’s Cockatoo was inspecting the hollow; subsequently the hollow was used, with a nestling later banded. Given that the numbers of Major Mitchell’s Cockatoo and Red-tailed Black-Cockatoo breeding at Koobabbie also increased during the same period (Alison Doley
One salient point when considering competition for hollows is that unlike the other cockatoos, which only frequent the nest hollow during the breeding season, Galah guard their breeding hollow throughout the year (
The six largest artificial hollows were used by Carnaby’s Cockatoo during more than half of the hollow-years they were available. Natural hollows formerly used by the cockatoos that were repaired were used soon after being repaired. The rapidity with which the artificial and repaired hollows were taken up and used indicates that the provision of artificial hollows and repairs of natural hollows are useful strategies for bolstering the stock of nesting hollows.
Of 60 breeding attempts where nestlings could be measured from 2003 to 2008 (inclusive), 15.0% resulted in nestlings whose body mass were more than one standard deviation below the benchmark established from nestlings at Coomallo Creek. This is similar to the incidence of Coomallo Creek nestlings being in poor condition (11.4%), and much less than the 63.0% recorded at Manmanning. These results indicate that the Koobabbie population was producing healthy nestlings, and was not subject to the same food shortages that led to the extirpation of the population at Manmanning, and a number of other areas throughout the eastern part of the range of the species (
The movement records of two fledglings from Koobabbie indicate that the population moves to the coast at the end of the breeding season, and congregates with birds from other breeding populations in the northern wheatbelt (
Plausible causes of the 2009 deaths include toxicity, infectious disease, or an adverse weather event.
The reason for the deaths occurring at Koobabbie and not at other similar breeding sites, such as Coomallo Creek, remains unknown, as similar food sources and agricultural practices are present in each area. However, there could be differences in relation to specific methods of agricultural practice, or environmental factors at Koobabbie or adjacent farms that increase the chances of exposure for the birds. What is important is that these data were recorded and shared for future reference (
Koobabbie is the only Western Australian IBA on a private property on which long-term research is encouraged by the owners. This research is important for several reasons. The first relates to Alison and John Doley’s approach to conservation. For over 25 years they have kept records of the avifauna of the property, and made the data freely available for others to use (
Until 2009, the population of Carnaby’s Cockatoo on Koobabbie was regarded as one of the most important in the northern wheatbelt. There were at least 27 pairs breeding on the property, and active research and management was carried out. As a result, Koobabbie was known colloquially as “Cockatoo Club Med.” However, without this long-term study involving many individuals and organisations, the impact of the 2009 and 2012 mass deaths may have gone unreported. These catastrophic events reduced the breeding population by approximately 80%, and illustrate the impact of stochastic events. The danger is that with such small numbers now breeding on Koobabbie, other factors may come into play and lead to the extirpation of Carnaby’s Cockatoo on the property, as has happened in other areas of the range of the species (
Knowing that large hollow-bearing trees are being lost on Koobabbie, and replacement stock takes a century or more to provide a hollow for Carnaby’s Cockatoo (
As a result of changes in land use in the southwest of WA, conditions have favoured some species, which have increased in range and/or abundance, including Galah and Western Corella (
It is ironic that Koobabbie has been also designated as an IBA for Western Corella, when it has been subject to control on the property. Western Corella is common through much of the northern wheatbelt with flocks of up to 3,000 seen at Dalwallinu (60 km south-east of Koobabbie), Dongara (143 km north-west), Geraldton (197 km north-west), and Morawa (80 km north) (
If Canola as a feed source is beneficial to Carnaby’s Cockatoo, it should not be used to justify the continued clearing of native proteaceous vegetation. This can now occur under the WA native vegetation clearing regulations, which allow isolated trees and up to 5 ha/year to be cleared without the need for a licence to clear (
At present there is no quantitative estimate of the extent of private property providing breeding and feeding habitat for the species. It is also important that the extent of suitable habitat is established, and incentives developed to encourage more farmers to emulate the example of the Doleys in making nature conservation an objective of their management, and monitoring the outcomes of that management.
We acknowledge the following for assistance: Tom Kemp and Bob Veletta who assisted with the monitoring of breeding Carnaby’s Cockatoo and repairs of derelict nest hollows from 2003–2013; John Koch for monitoring in 2013; Neil Johns and members of the Sporting Shooters Association of Australia – Western Australia (Inc) who have controlled over-abundant Western Corella and Galah on Koobabbie under licences TF 006233, TF006010, TF005833, TF005677, TF005017, TF004366, TF003762, TF003258, TF002812, TF002680, TF002813 and TF002681 to take fauna for educational or public purposes; Wally Kerkoff who made the artificial hollows; staff at Perth Zoo for fieldwork and some processing of tissue samples; Dejan Stojanovic, Conservation Officer for the Birds Australia Carnaby’s Black Cockatoo Recovery Project for monitoring; and Dave Pongracz of WA Department of Parks and Wildlife for preparing Figure