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Integrating conservation with production: The ecology of three threatened black cockatoos within a mining production landscape in the Jarrah-Marri forest of Western Australia

Lee, Jessica (2013) Integrating conservation with production: The ecology of three threatened black cockatoos within a mining production landscape in the Jarrah-Marri forest of Western Australia. PhD thesis, Murdoch University.

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Three threatened black cockatoos inhabit the Jarrah Eucalyptus marginata-Marri Corymbia calophylla forest of southwestern Australia: Baudin's Cockatoo Calyptorhynchus baudinii, Carnaby's Cockatoo C. latirostris, and the Forest Red-tailed Black Cockatoo C. banksii naso (FRTBC). Their local ecology in relation to anthropogenic disturbance is poorly known, hampering conservation management. This study investigated their ecology at the Newmont Boddington Gold (NBG) mine, 130 km southeast of Perth, Western Australia, along the eastern margin of the Jarrah-Marri forest. To improve the scientific basis for conserving black cockatoos and their habitat at NBG, I aimed to: (1) describe the ecology of the three species at NBG, particularly group size, site occupancy, habitat use, and food plant use (including seasonal and interannual changes); (2) examine the effectiveness of ground-based hollow surveys, postfelling inspections of hollows, and behavioural observations for assessing black cockatoo breeding habitat; (3) assess the successional stage of the rehabilitated mine pits and characterise variation in the structure and floristics of pits, in order to identify features that might influence the availability of food resources for black cockatoos; (4) document feeding activity by black cockatoos within rehabilitated mine pits and any associations with structural or floristic features; (5) trial artificial nest hollows to support breeding on-site and compensate for the loss of natural hollows; (6) review the use of artificial nest hollows for black cockatoos to assess their value for mitigating natural hollow loss; and (7) investigate black cockatoo use of natural and artificial water sources at NBG and assess the potential for black cockatoo interactions with residue disposal areas.

All three black cockatoos used remnant forest habitat as well as human-modified habitats such as mine-site rehabilitation, water sumps, farm paddocks, and pine plantations. Carnaby’s Cockatoos used the broadest range of habitats and fed on at least ten plant species at NBG. FRTBC showed similar group sizes and occupancy across seasons, suggesting year-round residency. In contrast, group size and occupancy changed across seasons for Carnaby’s Cockatoos, indicating migrating flocks as well as some birds present year-round. Few Baudin’s Cockatoos were observed in spring and summer, but they were more abundant during autumn and winter, which is when flocks migrate northwards.

Three methods – ground-based surveys, post-felling inspections, and behavioural observations of black cockatoos – were used to describe the availability of potentially suitable nesting hollows across three tree species (Jarrah, Marri, Wandoo E. wandoo) and to document probable nest sites. Eleven probable black cockatoo nest hollows were identified at NBG and surrounds (Carnaby’s Cockatoos: n = 7; FRTBC: n = 3; and unknown black cockatoo species: n = 1). Behavioural observations, using visual or acoustic cues followed by physical ‘tree-knocking’, were the most effective approach to identify probable nest hollows (n = 10 hollows). Ground-based surveys yielded only one probable nest hollow, while post-felling inspections identified none, despite large sample sizes and extensive field survey periods. Of the probable nest hollows, six were in Marri, four in Wandoo, and one in Jarrah. Ground-based surveys identified 149 potential hollow-bearing trees, of which 119 (80%) survived felling intact enough for inspection. Few potential hollows in Jarrah were large enough for black cockatoos (n = 28 of 89 trees inspected, 31.5%). Large hollows occurred more frequently in Marri (n = 14 of 22 trees inspected, 63.6%) and Wandoo (n = 8 of 12 trees inspected, 66.7%).

Thus ground-based surveys may significantly overestimate potentially suitable hollows, but they may provide useful assessments of relative hollow abundance if biases are identified and corrected. Post-felling inspections are ineffective at characterising hollow occupancy, but provide other data. Targeted behavioural observations are most reliable for identifying probable nest hollows, provided that surveys are undertaken at dawn and dusk during known breeding seasons.

The rehabilitation pits at NBG were 7 - 10 years old and in an early successional stage, with a wide range of proteaceous vegetation. The larger myrtaceous trees were becoming prominent and will eventually shade out the proteaceous understorey. Carnaby’s Cockatoo fed on seeds and flowers from proteaceous shrubs (Banksia and Hakea spp.), while Baudin’s Cockatoo and FRTBC fed on Marri seeds. Examination of food residues proved critical in demonstrating feeding activity by FRTBC within rehabilitated mining pits, as FRTBC were not observed. No particular floristic or structural features characterised feed plots relative to non-feed plots, suggesting little support for substantially altering rehabilitation prescriptions to cater to the food requirements of black cockatoos. Rather, food availability within rehabilitated areas reflects vegetation succession, with fast-maturing proteaceous species providing abundant food in young rehabilitation sites, followed by regenerating eucalypts (e.g. Marri). Therefore, as succession proceeds and the structure (and species composition) of the vegetation becomes closer to that of the native Jarrah-Marri forest, the availability of habitat resources is likely to change. Rehabilitation of mining pits can provide shortterm benefits for black cockatoos, emphasising the broader value of revegetating landscapes to support black cockatoo conservation. However, tree hollows suitable for breeding take over a century to form, so conserving old, hollow-bearing trees complements restoring food plants.

Trials of plastic and wooden artificial nest hollows (ANHs) at NBG by black cockatoos yielded no observations of inspection or nesting by black cockatoos. This likely related to ANH position (i.e. too low in the tree) or location (i.e. far from an established nesting site), and the presence of sufficient natural hollows locally. A state-wide survey of ANH use by black cockatoos in Western Australia was also undertaken. Responses indicated that ANHs have been widely used (at least 157 ANH installations) in Western Australia from as early as 1996. Three major ANH designs have been used: ‘cockatubes’, hollowed-out log sections, and wooden box-type ANHs. Black cockatoos nested and reared young in all designs. Most observations of black cockatoos using ANHs involved Carnaby’s Cockatoos. There were few records of ANHs by FRTBC and none by Baudin’s Cockatoo. Thus ANHs may present a short-term mitigation option, especially in areas deficient in natural hollows. However, over the long-term, they cannot substitute for natural hollows.

Observations of black cockatoo drinking sites at NBG documented the use of both natural and man-made water sources. The site, and the surrounding landscape, provides water for black cockatoos across the year. Black cockatoos prefer water sources with firm and gently inclined edges surrounded by vegetation. They rarely came into proximity with potentially hazardous sections of the Residue Disposal Areas (RDAs). RDAs may be less attractive because they occur in very open landscapes. Black cockatoos used faunal drinking points around the RDAs, suggesting that they minimise black cockatoo-RDA interactions.

Overall, the three black cockatoos exhibited different ecologies within the same landscape, differing in their responses to disturbance and their capacity to use anthropogenic resources. Significantly, the value of young rehabilitation for feeding indicates that feeding habitat can be restored on a scale of a decade or two rather than waiting for nearly a century as the forest matures. Breeding resources, however, are only restored naturally on a scale of centuries, placing a premium on conserving prime breeding habitat and artificial supplementation of the breeding hollow resource.

Given that much of the remaining Jarrah-Marri forest is within the tenure of State Forest or mining companies such as NBG, there is considerable scope for adaptive management initiatives to further inform conservation actions for black cockatoos. These initiatives could investigate: (1) management of orchards; (2) captive breeding; (3) general population ecology and baseline data collection; (4) issues related to nesting hollows; (5) management issues specific to mine-sites; and (6) management issues relevant to forested areas of the southwest, in particular State Forest.

Publication Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor: Calver, Michael and Finn, H.
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