Ecologists from the Conservation Forensics Laboratory of the Research Division for Ecology and Biodiversity at the University of Hong Kong (HKU) have applied stable isotope techniques to determine whether birds in the pet trade are captive or wild-caught, a key piece of evidence required in many cases to determine whether a trade is legal or not. They have applied this technique to the yellow-crested cockatoo (Cacatua sulphurea, YCC), a critically endangered species from Indonesia/Timor-Leste with a global population of fewer than 2,500, according to the International Union for the Conservation of Nature (IUCN). Threatened by overexploitation for the pet trade, Hong Kong has a sizeable population of 150-200 individuals which was established through the release of birds transported here as pets.