 The northern subspecies T. b. velox and T. b. thalassina are in breeding plumage from May to September or October , whereas the relevant period for the two southern African races is from December to April . For T. b. cristata , the moult timing depends on location ; birds from Australia and Oceania are in breeding plumage from September to about April , but those in Thailand , China and Sulawesi have this appearance from February to June or July . 
