Bali starling breeding & conservation (Balen, 1994)

B. van Balen (ICBP Indonesia Programme, Indonesia) & V.H. Gepak Kebun Binatang Surabaya, Indonesia (1994) - The captive breeding and conservation programme of the Bali starling (Leucopsar rothschildi). Creative Conservation: Interactive management of wild and captive animals. Edited by P.J.S. G.M. Mace and Feistner. Published in 1994 by Chapman & Hall, London. ISBN 0 412 49570 8, Captive stock world-wide.

24.1 Introduction

The Bali starling (Leucopsar rothschildi) is a strikingly beautiful silky-white bird with black tips to the flight feathers and blue naked skin around the eyes. It was first described and placed in a monotypic genus by Stresemann in 192, a year after he discovered it in the dry lowland forest along the coast of northwest Bali (Stresemann, 1912). Since its discovery the numbers have declined and its distribution has receded. In the 1920s it occupied roughly 30.000 ha of uninhabited land (Paardt, 1926; Plessen, 1926; Helvoort, 1990), but with the progressive conversion of forest to agricultural land, by the late 1980s its range had shrunk to less than 4000 ha and the population was restricted to a small part of the Bali Barat National Park in the northwest of the island (Helvoort, 1990). In the last 20 years the decline in numbers has been accelerated by trapping for the international pet trade and an increased demand from aviculturists. By 1990 the total wild population was estimated to be as low as 13 (Balen and Soetawidjaya, 1991). The Bali starling has been included in the IUCN Red Data Book since 1966, in the Endangered category, and international trade is prohibited under the Convention on International Trade in Endangered Species (CITES). Since 1970 the species has had absolute protection under Indonesian law.

In 1983 the Indonesian government, represented by the Directorate-General of Forest Protection and Nature Conservation (PHPA) formally requested the International Council for Bird Preservation (ICBP) to draw up and put into action a conservation project for the Bali starling. The implementation of this project was preceded by a feasibility and preparation period of 1983-1986 (Helvoort, Soetawidjaja and Hartojo, 1986), and by 1987 PHPA, ICBP, the American Association of Zoological Parks and Aquariums (AAZPA) and the Jersey Wildlife Preservation Trust had produced a comprehensive five-year cooperative programme.

The agreed overall aim was to restore a viable and self-sustaining population in Bali Barat National Park. The objectives included:

(a) monitoring and protecting the birds in the wild;
(b) establishing a captive breading programme in Indonesia with input from other captive breeding programmes in America, Jersey and elsewhere;
(c) restocking the wild population;
(d) promoting public awareness.

A further three-year plan was agreed in 1992 which continued the original aims and expanded the objectives to include:

(a) stopping the illegal capture of birds;
(b) reducing the demand for wild-caught birds;
(c) establishing new populations within the species' dispersive range from captive stock
(d) continuing to promote an awareness of the cultural and aesthetic value of conserving the Bali starling in the wild;
(e) undertaking management-orientated studies of the behaviour and ecology of the species;
(f) developing the capability of the Bali Barat National Park to be self-sufficient in conserving the species.

24.2 Captive stock worldwide

Fortunately there has been for some time a relatively large captive population in zoos, bird collections and private collections worldwide. This population has been estimated to be in excess of 700 individuals (Helvoort, 1990), but only recently has there been an attempt to cooperatively manage parts of this scattered population. Poor record-keeping and uncontrolled breeding has made any analyses and management difficult. There are two regional studbooks, which do provide usable data. One, the American studbook, which is under the auspices of AAZPA and one of their Species Survival Plans (SSP), recorded as of July 1992, 381 birds in 68 participating institutions (Seibels, 1992). The other, which is under the auspices of the Federation of Zoological Gardens of Great Britain and Ireland, registered as at the end of 1991, 110 birds in 20 institutions (Fisher, 1992). In Europe the European Association of Zoos and Aquaria (EAZA) has approved the setting up of a coordinated breeding programme (EEP).

24.3 Captive breeding programme in Indonesia - 1 Breeding stock

In August-November 1987 the breeding facility already in existence in Surabaya Zoo in east Java was renovated. This facility comprised 29 aviaries with 16 Bali starlings. In November 1987 the captive population was increased with the addition of 37 birds donated by zoos and private collections in the USA and by Jersey Wildlife Preservation Five of these birds, most of them over 10 years old, died shortly after arrival. In 1992 the breeding stock in Surabaya Zoo consisted of 44 birds, with 18 birds (11 male, seven female) born before 1985, 10 birds (four male, six female) born in 1985 or later, and 16 birds (six male, eight female, two unknown) of unknown age, but all born before 1987.

24.3.2 Husbandry

A number of publications on breeding Bali starlings have appeared in the last two decades (Taynton and Jeggo, 1988; Partington et al., 1989; see also bibliographies in Seal (1990) and Seibels (1991). Husbandry used in Surabaya Zoo followed the guidelines given by American zoos (Seibels, 1991) and a brief account only is given here.

The breeding aviaries for single pairs were at least 2.5 m high, 2.5 wide and 4 m deep, well-planted with low shrubs and small trees. Breeding results during the first season were disappointing and measures to enhance productivity were taken:

(a) aviaries screened in order to avoid interaction with starlings in adjoining breeding units;
(b) in 1989 the old nest-boxes were replaced by boxes that followed a design widely used in the USA (Seibels, 1991);
(c) disturbance from visitors to the zoo was decreased by closing off the immediate surroundings of the aviaries;
(d) birds with poor breeding performance were repaired;
(e) in addition to dry food pellets, fresh local fruits (papaw, bananas) and live food (mealworms, ant pupae) provided.

24.3.3 Breeding results

Egg hatching during the year was satisfactory. Mortality, however, after hatching remained high and to date an average of only six to nine birds reach maturity each year. The introduction of new nest-boxes in August 1989 resulted in some increase in the number of clutches, but the chick mortality stayed high. To date 39 birds have been successfully raised. 

Figure 24.1 shows the breeding results for 1988-1992. As three pairs that were amongst the most productive of the breeding stock, were stolen in March 1991, the period April 1991 to July 1992 has been omitted from the graph. The stolen birds were retrieved in the second half of 1992.


Figure 24.1 (above): Breeding results of the Bali Starling Propagation Centre at the Surabaya Zoo, 1988-1992; reliable figures for the period were not available (I: January-March, II: April-June, III: July-September, IV: October-December; solid bars: number of eggs laid; grey bars: hatchlings, white bars: successfully fledged birds) - [vertical axis: Numbers of eggs and birds], p.424

24.3.4 Studbooks

In order to manage the captive population scientifically, and in particular to minimize inbreeding, carefully maintained studbooks are essential. American and British birds are already registered, and regional studbooks for birds in Indonesia and in Europe are being prepared. Other studbooks should be prepared for birds held in Japan and Singapore.

Taynton and Jeggo (1988) found evidence of increased chick mortality with higher inbreeding levels in Jersey birds, and Helvoort (1990) reported an inbreeding depression in the American population leading to a reduction in fertility. A recent study (Thohari et al., 1991) indicated an extremely low heterozygosity of certain blood protein types in the captive population held in Indonesia, with as yet unknown implications for the species. The introduction of wild-caught Bali starlings, of which a fair number are still in private hands, in Java and Bali would diversify the captive gene pool.

24.3.5 Minimal viable population

It has been tentatively suggested that for a species' long-term survival a minimum effective population of 500 individuals is needed (Franklin, 1980). More specifically a recent population viability analysis (PVA) (Seal, 1990) considered that to be viable, 100 birds in the wild and another 1000 in captivity were desirable, with these two populations being managed as a single meta-population. These numbers are based on little empirical data and their feasibility (especially with regard to the wild population) is doubtful, but it is clear that more birds will decrease the risk of genetic deterioration and extinction. The zoos and private collections in the USA can together house only a restricted number of birds. Those registered in the studbook are closely managed and monitored, as are those in the British studbook, but there are many in the widely scattered world captive population which are outside any managed breeding programme. Coordination amongst collections is necessary to increase the effective size and viability of the captive breeding programme.

Of the 44 birds at present in the Surabaya zoo only four are successful breeders. Recombination of the pairs, especially among the groups of different origin, is essential to enhance productivity and increase the effective breeding population. The extension of the Indonesian propagation programme to other sites would increase the size of the Indonesian captive population and the number of birds for release. To this end, birds obtained under a one-time amnesty campaign from local private owners in exchange for captive-bred birds brought over from the USA (in June 1992, 17 birds were brought over for this purpose), and those handed over directly with the help of local PHPA officers, are now being registered. To date more than 80 birds have been registered and fitted with transponders. In 1993 they will be placed in the new additional captive breeding centres, or be released into the wild, if considered appropriate.

24.3.6 Release programme

The building of a Pre-release Training Centre (PTC) in the Bali Barat National Park was completed in June 1988. The unit comprises 10 aviaries each 5x3x2 m and follows the design of the Captive Propagation Centre in Surabaya zoo. The PTC is located in an off-public site, with restricted access for interested visitors. The aviaries are sufficiently isolated to reduce any habituation to humans, including the bird keeper.

In autumn 1987, when less than 50 birds survived in the wild, a release was felt to be justified. In July 1988 the first group of three birds from the Surabaya zoo was accommodated in the PTC. To adjust the birds to their future environment, they received six week's training which focused on developing skills for foraging in the wild, retaining fear of humans, and gradually accustoming the birds to the boxes in which they were to be transported to the release site. In the field, the birds were released in turns during the first week, in order to maintain the birds close to the release site - the caged birds always attracted the ones already released. This attempt resulted in one known casualty and the disappearance of the other two birds. The extremely dry conditions and strong wind at the time of release, the birds unfamiliarity with the area, and the location of the site distant from any known Bali starling roosting area may have been contributory factors which caused the failure (Helvoort, pers. comm.)

During the Bali starling PVA workshop, held in Bogor, Indonesia, and attended by an international group of conservationists, aviculturists, and other experts (see Seal, 1990), it was decided that a second attempt to release captive-bred birds into the wild population should be undertaken as soon as possible.

Accordingly, in April 1988, eight captive-bred birds were brought over from Surabaya Zoo to Bali. One bird died shortly afterwards, probably due to stress, and another was considered unfit for release. The birds were given various kinds of wild fruits, which were known to have been eaten by Bali starlings. They readily took various arthropds, including scorpions and millipedes, and small reptiles, that entered their cages. They showed instinctive reactions towards raptors flying over. In early 1990, two birds confiscated in east Java were added to the PTC group; one of these was considered for release, but the other was assumed to be unfit for release as its malformed bill suggested it had been hand-raised.

In April 1990 another six captive-bred birds were transported from Surabaya Zoo to Bali Barat and housed in the PTC. The second attempt was planned for a location in the far northeast edge of the Prapat Agung Peninsula in Bali Barat, a short distance form the Teluk Kelor guardhouse. Here wild Bali starlings were known to roost regularly. A two-compartment simple cage (2x2x2.5 m) was built on the site to serve as training accommodation. On the day the birds were transported to the release site, transponders were inserted, and colour rings were attached. Special heavy-duty rings designed for the Bali starling conservation programme were attached to the two confiscated birds, whilst the other birds had their metal zoo rings. In order to tell the released birds from the wild birds during at least the first weeks, the breast feathers of the birds to be released were dyed red with rhodamine B. Two coloured plastic spiral rings were attached to all the birds, each coded with a unique combination of numbers. On April 15 1990, the first four birds were released from the cage where they had been housed during the previous two days. On April 17, three birds were released, followed by two, two, one and one on each consecutive day. Birds unfit for release stayed in the cage to decoy released birds back to the cage, where food and water were provided during the first weeks. The wild-caught confiscated bird that was released with the captive-bred birds, and which was expected to act as a sort of guide was a disappointment: immediately after its reluctant take off, it flew away in a direct line and was never seen again.

Daily monitoring of the starlings by telescope (20-60x) from a hide near the release site was maintained during the first weeks, where food pellets, fruits and drinking water were provided. Acceptance of the wild by the released birds went smoothly and soon mixed foraging, communal anting and roosting flocks could be seen. One pair was formed within one week and the wild bird would follow its partner close to the food and drinking water container. The observation of several birds around the site, but not at the drinking place soon after release, suggested that acclimatization was rapid in some cases.

Reading of the ring codes became increasingly difficult, as the birds became more wary in the process of adaptation, making the success rate hard to assess. This was aggravated by unexpectedly high poaching pressure near the sites. Within one month one of the released birds, detectable by its transponder, was rediscovered in the hands of a local bird dealer, and an unknown number of other birds may have been trapped. In early October 1990, however, six months after the release, a marked bird was identified about 8 km from the release site. It was observed copulating with a wild bird (in the kapok plantation enclave along the main road that cuts through the National Park), but disappeared soon after. In November the same year, another released bird was rediscovered, paired to a wild bird. In January the following year this pair successfully raised three young in a tree hole not far from the release site.

A major decline in numbers of Bali starlings was found during the pre-breeding census of 1990. Even with the 13 released birds, numbers had dropped to some 15 birds largely due to poaching. The following breeding season guarding of the park was increased, but no releases took place, primarily because sufficient [data were?] not available from the Surabaya breeding facility. Poaching appeared to be better controlled, though still going on, and the post-breeding censuses completed in June 1991 and June 1992 showed about 35 and 55 birds, respectively (Figure 24.2). Eight occupied nests were located in the Teluk Gondang area. Only natural nest holes were used, and again the nest-boxes provided a few years ago were ignored.

24.3.7 Disease

Though a quarantine period in the PTC is common practice before release, and the birds kept in the zoo are examined regularly, there is still a considerable risk of disease transmission. The incidence of atoxoplasmosis in captive Bali starlings in American zoos (Partington et al., 1989) is especially worrying. Following a discussion paper prepared by PHPA and ICBP, an AAZPA team came from the USA in August 1992 to examine the birds held in Indonesian zoos and in the PTC in Bali. A medical quarantine protocol for all birds to be released and for birds held in captive breeding centres has since been developed (Appendix 4 of Balen and Jepson, 1992).


Figure 24.2 (above): Bali starling numbers in the Bali Barat National Park, 1983-1992 (after van Balen and Jepson, 1992), p.428

To further reduce the risk of disease transmission, release in the future will be in former, but now empty, Bali starling habitat. This reintroduction as opposed to restocking, will involve rather different and more elaborate release techniques, as no resident guides will be available. An intensive field study is being prepared by ICBP and AAZPA, aimed at collecting data on behaviour and breeding success of released birds (M. Collins, pers. comm.). A possible release site has been identified on the island of Menjangan, pending more information on diseases in the captive population and full control of poaching in the area. Furthermore, the use of radio-telemetry is being considered and preliminary tests on captive starlings has had promising results (Elbin et al., 1991).

24.4 Conclusion

Habitat availability in the present National Park as a limiting factor on the recovery of the Bali starling is currently being investigated by the project. There may not be enough suitable habitat in the national park to support more than a three- or fourfold increase in the present population of 55 Bali starlings. Even if attained, this figure would be far below any number suggested for a viable population. Any continuation of the release programme will have to take this into account and the conversion of the plantation enclaves that exist in the Bali Barat National Park into Bali starling habitat must keep pace with an increasing number of starlings.

Considerable time and effort has been put into the captive-breeding programme, but to date its success in terms of contribution to the conservation of the Bali starling has been limited. The recovery of the wild population following the improvement in protection shows that other techniques can be possibly more immediately efficient. However, the potentially deleterious consequences of inbreeding cannot be discounted and the introduction of new genes is justified. Further releases are planned for 1993 and feasibility studies are now being carried out. To avoid disturbance of the present wild population, sites in Bali starling habitat other than the previous ones will be selected.


The Bali Starling Project Phases 1-3 would not have been possible without the assistance and commitment of a large number of people and institutions. The Project is managed by ICBP and financed by AAZPA and the New York Zoological Society, Liz Claiborne/Art Ortenberg Foundation, and JWPT. The PHPA head offices, the Bali Barat National Park and Surabaya Zoo were the local partners in the implementation of the Project. In particular, M. Noer Soetawidjaja, Slamet Suparto and Made Rasma c.s. were most closely involved in the release programme. Thanks are forwarded to the former Bali Starling Project officer, Bas van Helvoort, for the discussions and support provided during the early stages of the project, and to Paul Jepson and Professor H. Prins for their valuable comments on an early draft of the paper.


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  • Balen, B. van & Gepak, V.H. (1994) - The captive breeding and conservation programme of the Bali starling (Leucopsar rothschildi). Creative Conservation: Interactive management of wild and captive animals. Edited by P.J.S. G.M. Mace and Feistner. Published in 1994 by Chapman & Hall, London. ISBN 0 412 49570 8, Captive stock world-wide

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