'Survival ecology': an urgent ecological study of birds imperilled by the cage-bird trade across Java and Bali, Indonesia

Squires, Thomas Michael (2023) 'Survival ecology': an urgent ecological study of birds imperilled by the cage-bird trade across Java and Bali, Indonesia. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Throughout Southeast Asia, the trade in wild-caught songbirds—prized for their vocal ability, plumage, rarity and cultural significance—is having a massive effect on wild populations, such that an Asian Songbird Crisis was declared in 2017. Indonesia, particularly its most populous island of Java, is widely regarded as the epicentre of Southeast Asia’s cage-bird trade, with millions of birds sold annually at markets irrespective of their legal status and astonishing levels of bird ownership that have led to estimates that there may actually be more songbirds kept in cages across Java than there are in the wild. The aim of this thesis was to understand the ecology and management needs of some of the passerines most threatened by the cage-bird trade across Java and Bali, Indonesia, to guide in situ conservation actions. First, I implemented a citizen science event in Java and Bali to gather bird occurrence data and examine the potential for citizen science as a conservation tool in Indonesia. I then used these data to model the distributions of 23 of Java’s lowland birds in order to assess the convergence between the current distribution and previous distribution maps and the network of protected areas. Following this, I studied the ecology and conservation management of two of Java and Bali’s most endangered sturnids, the Black-winged Myna (Acridotheres melanopterus) and Bali Myna (Leucopsar rothschildi). There are large existing gaps in biological data coverage that hinder efforts to generate robust baseline information on the distribution and abundance of birds across Java and Bali. I attempted to address this by designing and implementing a month-long citizen science event, ‘BigMonth2020’, which had the dual aim of engaging Indonesian society in citizen science and generating a large bird occurrence dataset. The event was publicised through social media and incentivised with grants and competitions. A huge number of bird records (n = 102,887) were submitted to the ‘Burungnesia’ phone app during the event, resulting in a massive increase (147%) in spatial coverage of data, so that now 79.3% of grid squares contain at least some data. Three quarters of Java and Bali’s bird species (n = 353) were recorded and this included 27 globally threatened species, many of which were recorded in new areas. The event was more inclusive in terms of female participation (23.4% of participants were female) than other bird- related pastimes in Indonesia, such as bird-keeping and songbird contests, and the vast majority (71.8%) of participants were under 30-years old. The project cost less than US$10,000 to run, and serves as a model for rapidly establishing a distributional baseline for monitoring biodiversity trajectories. The current distributions of many of Java’s lowland passerines remain poorly understood, and this lack of baseline data precludes efforts to monitor distribution changes in threatened species. Data generated from BigMonth2020 were combined with other citizen science bird datasets available for Java (eBird, Burungnesia and the Indonesian Bird Atlas) to assess the current distributions of 23 of Java’s lowland birds. Most species exhibited relatively patchy distributions that were often significantly smaller than existing estimates for their extent of occurrence. Among the environmental variables used in modelling, land-cover-based predictors were ultimately the most important in the models for the majority of species (20/23), with landscape-scale habitat diversity, the proportion of forest, and the proportion of cultivated land most commonly the most important predictor. The lack of convergence between the current distribution of the modelled species with Java’s formally protected areas suggests that future conservation for these and other lowland birds, which are likely to come under increasing anthropogenic pressure, will need to occur alongside people and involve other effective area-based conservation measures (OECMs). My findings highlight the considerable value of continued citizen science efforts across Java, and indeed elsewhere in data-poor yet biodiverse regions. Sturnids are popular cage-birds owing to their vocal ability and the bold colours and striking patterns of their plumage and in some cases bare facial skin. As a result, there have been disastrous population declines in some of Java’s sturnids. I documented the plight of the Black-winged Myna, a Java and Bali endemic that has been trapped to near extinction. I estimated the current range and population size of the species at Baluran National Park, which supports Java’s last known population, and used species distribution modelling to evaluate the suitability of currently unoccupied areas across the park to identify priorities for management intervention. I estimated that the Black- winged Myna population numbers 179 individuals (95% CI: 111–288) and that its current range is restricted to a small area (12.3 km2) of savanna and dry deciduous woodland, while my model indicated that a considerable extra portion (72.1 km2) has potentially suitable habitat. I inferred that the main cause for the disparity between its current and potential range is trapping, compounded by savanna loss and degradation due to overgrazing by cattle and the spread of invasive thorny acacia (Vachellia nilotica). The recent partial clearance of acacia appears to have assisted a modest population recovery by the myna, but its further population growth depends on effective management of illegal poaching, further clearance of acacia, and easing grazing pressure on areas of savanna, particularly through engagement with human communities living inside the park. Continuing with the theme of studying endangered sturnids, I measured the viability of the Bali Myna population at Bali Barat National Park (BBNP). Despite decades of conservation efforts, in the 2000s it was reported that there were probably no Bali Mynas left in the wild, and it is unlikely these reports would be false considering how well-known the location of the last individuals’ was and that mynas can be readily detected by call. Since then, reintroductions of captive-bred birds and other management interventions have led to population growth. To plan for the next decade of conservation management, I modelled the Bali Myna population at BBNP to explore the effects of (1) changes to population supplementation and (2) an increase in trapping intensity. A baseline model was validated using population census and captive-bred release data from the last ten years and the model was projected ten years into the future. The population was predicted to increase under current levels of supplementation, while stopping supplementation in five years had only a small effect. I modelled the differential effects of two trapping methods used by poachers and three trapping volumes. The population was resilient to low levels of trapping with and without population supplementation but declined under high levels of trapping. On current trajectory, I estimated that the population will approach self-sustainability in the next 5–10 years. The supplementation programme at BBNP could then either be scaled back or repurposed as a translocation project to expand the myna’s range, and nest- boxes could be used to support population growth. There is much more work needed to address issues related to the Asian Songbird Crisis, and I conclude by providing some recommendations for future work that are related to the topics covered in this thesis. Among these are the need to continue to grow citizen science efforts across Indonesia, a recommendation for urgent fieldwork to understand the status of at least three of Sulawesi’s six island endemic sturnids (and indeed other Indonesian sturnids that are poorly known), a call for community-based conservation projects, and further ecological fieldwork to support reintroductions and conservation management of threatened species.