Ongoing and emergent threats to yellow-crested cockatoos (cacatua sulphurea) : a critically endangered species surviving in a city

Abstract

The Yellow-crested Cockatoo (YCC; Cacatua sulphurea) provides a case study into an increasingly common conservation paradox – a species in decline in its native habitat, yet established with a growing population in an alien environment. Over-harvesting for the legal international pet trade in the 1980s is a major contributing factor to the critically endangered status of YCCs, and the reason ~10% of the world’s remaining wild individuals are now found outside their natural range in Hong Kong’s (HK) urban centre. This introduced population could serve an important conservation purpose for YCCs – as a genetic reservoir to safeguard the species from global extinction. Though less exposed to pressures faced by their native-range counterparts, such as habitat loss and illegal capture, the city cockatoos may instead encounter biological constraints in their new ex-situ environments. Here, I explore emerging threats to YCCs in their introduced home of HK, as well as ways to improve the wildlife trade systems that initially perpetuated the species’ decline. Firstly, I examine the scale, trends and systems by which thousands of species are legally traded, and recommend improvements that would facilitate timely detection of over-exploitation. I found that 95% of legal exotic pet trade 1997-2016 was declared using trade descriptions that solely indicate taxonomic class and above, limiting our ability to effectively monitor trade. I also found that during this period HK was the world’s 8th biggest wildlife trader. This points to an opportunity for impactful monitoring interventions in HK, and improved trade descriptions in pet trade. Secondly, I developed a forensic tool to differentiate wild-caught from captive-bred cockatoos, which would enable enforcement to detect whether protected, wild-caught YCCs are fraudulently declared as captive-bred and sold in legal markets. This tool detects significant differences between captive and wild cockatoos in stable carbon (p < 0.001) and nitrogen (p < 0.001) isotope values, as well as carbon isotope values in the amino acid valine (p = 0.009). In Chapters 3 and 4, I quantified the impact of habitat availability on YCC distribution in HK, finding that large nest trees (>50 diameter at breast height) are significantly more common (p = 0.021) in areas used by YCCs. Finally, I measured the level of competition for nest sites in HK and Singapore, where there is a small and declining YCC population. In >500 hours of field observations, I documented a higher frequency of antagonistic interactions around tree cavities in Singapore than HK, suggesting the YCCs might be outcompeted for critical breeding resources in Singapore, but not in HK. The YCCs demonstrate both the impact of unregulated wildlife trade and the opportunities provided by ex-situ populations. By highlighting areas of refinement for trade declaration and providing a forensic tool to identify illegally traded wildlife, I provide insight to mechanisms that perpetuate species decline. I also determine factors that restrict YCC expansion in an urban metropolis – information that can be applied to support the city cockatoos, maximise their potential role in global C. sulphurea recovery, and enhance opportunities for human-wildlife co-existence in cities.