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| The Red-tailed
Black Cockatoo in Victoria, South-eastern Australia:
Management of an Endangered Population
Joseph M. Forshaw
The Red-tailed Black Cockatoo Calyptorhynchus banksii is a familiar, locally common species across much of northern and central Australia. However, in southern regions the situation is quite different, for the two subspecies are confined to isolated tracts of forested habitat, and both are threatened. In far south-western Western Australia, west of the 600 mm isohyet, the subspecies C. b. naso is confined to Eucalyptus forests, especially where marri E. calophylla and jarrah E. marginata are prevalent, and is threatened by land-clearance. More seriously endangered is the subspecies C. b. graptogyne from south-western Victoria and neighbouring south-eastern South Australia, and it is this population that is the subject of our discussion.
Preliminary surveys undertaken in south-western Victoria by the Victorian Department of Conservation and Natural Resources revealed that the population comprised less than 1000 birds, and it was restricted to a small isolated geographical range in which both the feeding and breeding habitats were fragmented and threatened. Furthermore, it seemed that breeding involved only a small proportion of the population, less than 10 per cent, and it had been recorded only within the northern half of the range.
The cockatoos inhabit woodland of brown stringybark Eucalyptus baxteri in association with yellow gum E. leucoxylon and swamp gum E. ovata, surrounded by box buloke Allocasuarina luehmannii or drooping sheoak A. verticallata and river red gum Eucalyptus camaldulensis, the last often being remnant stands in cleared farmlands. During surveys carried out between December 1979 and November 1980, a total of 160 observations was recorded, and of these 81 per cent were in E. baxteri forest, 10 per cent were in remnant A. luehmannii open woodland, and 9 per cent were in stands of eucalypts other than E. baxteri.
Seeds of brown stringybark are the staple food, and for 10 or 11 months of the year the cockatoos feed exclusively on these seeds, which are taken when fully developed though still green. Investigations have revealed that it takes about 18 months from the time flower buds first appear on the trees for the fruits to reach the stage acceptable to the birds. This large green stage then remains on the tree for approximately 12 months, at which time the fruits become brown and hard, a stage not acceptable to the birds. The only other food that this population of Red-tailed Black Cockatoos feeds upon to any extent is the seeds of bulokes Allocasuarina luehmannii, and during most summers some birds move out from stringybark areas into remnant stands of bulokes along roadsides or on farmland, where they feed on the seeds from late December until early April. In the summer of 1991-92, there was a largescale movement into buloke areas, and it was suspected that this may have been in response to a lack of stringybark fruits or an abundance of buloke fruits.
During surveys carried out between December 1979 and November 1980, in south-western Victoria and south-eastern South Australia, 72 per cent of feeding observations were of birds taking E. baxteri seeds and 28 per cent of birds eating seeds of A. luehmannii. When undisturbed, the cockatoos will sit in trees throughout the day, opening up the fruits to extract the seeds, and a conspicuous accumulation of discarded husks, leaves and twigs builds up underneath the feeding trees. Presence of this debris is a useful guide to the presence of cockatoos in a particular area.
For nesting, the cockatoos require large hollows in large eucalypts, predominantly river red gums Eucalyptus camaldulensis, which originally were present in woodlands bordering watercourses or on loamy soils adjacent to stringybark forest. Unlike the stringybark forests, which were on sandy soil unsuitable for farming, these woodlands occupied arable lands, so were cleared for agricultural development. This very extensive land-clearance not only removed most of the nesting habitat, but also brought about strong fragmentation of the foraging habitat. A further consequence of agricultural development was differences in land tenure for the two habitats brown stringybark forests being retained in crown reserves, but river red gum woodlands going to private ownership.
Research into this endangered subspecies of the Red-tailed Black Cockatoo commenced in 1988, and in 1992 the Victorian Minister for Natural Resources and the South Australian Minister for the Environment approved the establishment of a Steering Committee to oversee and guide the research program. This committee comprised representatives of the Victorian Department of Conservation and Natural Resources, the South Australian National Parks and Wildlife Service, the Royal Australasian Ornithologists Union, and myself as representative of the World Parrot Trust, which was contributing funds to the program.
Early findings from the research demonstrated that loss of brown stringybark forests and river red gum woodlands are the main threat to survival of the cockatoos. Past clearing of the stringybark forests reduced this essential foraging habitat and caused the remaining areas to become fragmented. Frequent burning, particularly by intense fires which damage the canopies, presumably had an adverse impact on food resources. Old, dead river red gums left standing on farmland provide nearly all the nesting hollows, but now are under serious threat throughout the entire range. These remnant trees often are used as a source of firewood, and many are merely pushed over and burnt. This loss of available nest hollows seemed to be restricting natural recruitment into the population.
It soon became apparent that the co-operation and involvement of both the rural community and government departments would be required to ensure longterm survival of the Red-tailed Black Cockatoo in south-western Victoria and south-eastern South Australia. Consequently, it was decided that a local resident should be employed on a part-time basis to liaise with the rural community, both for enlisting the co-operation of farmers in conserving the birds and for obtaining additional information on their habits and status. Funds to meet the salary of this person were provided by the World Parrot Trust, and the appointment of Wayne Caldow, a farmer from the district in which the cockatoos presently nest, proved to be outstandingly successful.
This was the first time that a deliberate effort was made to involve the local farming community in a wildlife management program, and it was extremely beneficial. Tasks assigned to Mr Caldow were as follows:
· To establish a network of observers in the rural community which will feed back information on distribution, abundance, feeding and nesting of the Red-tailed Black Cockatoo.
· To gather breeding information from known nest sites.
· To search for other nesting locations and to obtain historical and current information on breeding sites from members of the rural community.
· To obtain information on feeding and food preferences.
· To liaise with landowners to protect nest trees and potential nest trees and to encourage the planting of river red gums and bulokes.
· To erect a few nest boxes in one of the nesting areas to ascertain if they will be used by the cockatoos.
The network of observers in the rural community (local residents, field naturalist clubs and schools) which was established in 1991-92 continued to provide Mr Caldow with records (eg. distribution, nesting, feeding) of the Red-tailed Black Cockatoo. This network was expanded during the 1992-93 and 1993-94 seasons and it now consists of some 65 sources. The records obtained from this network were entered on computer cards and were subsequently entered into the computerised atlas data base at the Department of Conservation and Natural Resources.
At the same time researchers focussed their efforts on the breeding biology because it was becoming increasingly evident that the apparently low recruitment rate posed a major threat to survival of the population. Twenty-three nests were found during the 1992-93 breeding season. This total was considerably higher than that for any of the previous four seasons of this study (1988-89, 12 nests; 1989-90, 13 nests; 1990-91, 7 nests; and 1991-92, 3 nests). However, seven of the 1992-93 nests failed, probably because of inclement weather in November and December and we suspected that most of the parents from these failed nests renested in nearby trees. If so, the total number of pairs (16) involved in breeding in 1992-93 was commensurate with those in 1988-89 (12 pairs) and 1989-90 (13 pairs). Because of nest failures and apparent renestings, the fledging of young birds was very asynchronous in 1992-93. The first fledgling was noted on 3 February (it may have fledged as early as 25 January) and the last indication that a chick was still in a nest was on 20 May.
Eleven nests were found during the 1993-94 breeding season. The eggs in two of these nests failed to hatch and a young chick disappeared from a third nest some time between 2 February and 10 March. The other eight nests either appeared to have fledged a young or had a large young present at our last inspection (10 March). Ten of the eleven nesting attempts were in the three known traditional nesting areas in Victoria while one nest was found in South Australia (the first nest found in that State during our study).
In 1993-94, nesting activity was recorded as early as 6 October and the first fledgling was seen on 4 February.
Of the 34 nests found during 1992-93 (23 nests) and 1993-94 (11 nests), seven were in hollows that had been used in previous years. The other 27 nests were found in trees where we had not previously recorded nesting. However, of these 34 nests, 31 were in one of the three known major nesting areas, and only three were located elsewhere. Thirty-three of the 34 nesting attempts were in dead trees or in supplementary nest hollows and one was in a live tree.
As the study progressed, we began to suspect that a reason for the low number of nests was the loss of hollows in traditional nesting areas. To test the feasibility of boosting the breeding capability of the population, we placed four supplementary nest hollows in dead trees which did not have suitable natural hollows. These supplementary hollows were set up at the conclusion of the 1991-92 nesting season, and during the following breeding season in 1992-93 a young Red-tailed Black Cockatoo fledged from one of the four hollows.
After the success of the 1992-93 nesting season, we placed an additional
six supplementary hollows in trees in traditional nesting areas. In addition,
because we were running out of dead trees in which to place the hollows,
we also obtained six disused wooden electricity poles, put them into place
in the areas and attached a supplementary nest hollow to the top portion
of each one. At the start of the 1993-94 breeding season, we had in place
16 supplementary nest hollows (10 supported by dead trees and 6 on electricity
poles) in traditional Red-tailed Black Cockatoo nesting areas. Of these
16 supplementary hollows, 5 (3 in dead trees and 2 on electricity poles)
were used by nesting Red-tailed Black Cockatoos in 1993-94. These 5 nests
represented 45% of the total Red-tailed Black Cockatoo nests found in
1993-94. We also recorded Yellow-tailed Black Cockatoos Calyptorhynchus
funereus, Slender-billed Corellas Cacatua tenuirostris, Australian
Results from the research program have enabled wildlife authorities, with co-operation from the local community, to implement a management regime to reverse the slow downward population trend that has occurred over the past 150 years. Key elements of this regime focus on protection of both foraging and nesting habitats as well as the continued provision of supplementary nesting hollows to assist the population until increased natural hollows become available. Preliminary results are encouraging.
Nest sites found since 1988 have been located on only thirteen properties; nine of these properties only had one nest each, while the most nest sites on a single property was 19 (not all active in the same year). Most landowners with nest sites on their properties were contacted during the 1992-3 and 1993-94 breeding seasons. Without exception, they were pleased to have the birds nesting on their properties and all indicated that they would not remove known nest trees. In most cases, they also indicated that few or no other dead standing trees (i.e., potential nest trees) would be removed. The landowners were also again informed about the possibility of eggs or nestlings being illegally taken from the nests. They were asked not to widely publicise the presence of nests on their properties and to report any suspicious activities to the authorities.
Mr Caldow has continued liaising with local landholders to encourage them to fence off areas from stock grazing so that regeneration of river red gums and bulokes can occur. In some instances the Department of Conservation and Natural Resources has supplied fencing materials to assist landholders with regeneration work on their properties.
The Royal Australasian Ornithologists Union maintains a monitoring role in overseeing implementation of the management regime and continues to support research into the breeding biology of this endangered subspecies of the Red-tailed Black Cockatoo. It certainly is true to say that future survival of the population has been enhanced greatly by field investigations undertaken during the past 20 years.