No one is quite sure how Hong Kong's yellow-crested cockatoo population came to nest in the city's cotton trees, but how the critically endangered birds arrived in Hong Kong is unequivocal - via the pet trade. Dr Astrid Andersson, a postdoctoral researcher at the University of Hong Kong has dedicated her scientific career to investigating the invasive species - and raising awareness of Hong Kong's role in legal and illegal wildlife trade - with the hope of helping conserve yellow-crested cockatoos before it is too late.