South Lantau is teeming with overwintering Danaids. Following the discovery of more than 2,000 Danaids in the area in early December, environmental group Green Power reported a larger swarm of over 5,000 individuals on its latest visit. Lo Wing-fung, Environmental Affairs Manager of Green Power, estimates the Danaids in South Lantau at above ten thousand, which is uncommon for the past decade.
The green group logged the latest record of overwintering Danaids on Dec 24 in a mixed woods valley of about 4,000 square metres bordering Lantau South Country Park. The Danaids aggregation was appraised at above 5,400 individuals, mostly of Blue-spotted Crow (Euploea midamus).
A Distance of Nine Kilometres between Two Overwintering Sites
Lo said about 2,300 overwintering Danaids were spotted early this month on Dec 9 in South Lantau within the area of Lantau South Country Park for the first time. The second visit to the same site in mid-December counted over 4,200 individuals, nine kilometres away from the latest visit on Dec 24. Lo believes the two sites hosted separate swarms of Danaids based on the difference in population size.
Lo noticed that some butterflies among the overwintering Danaids surveyed on Dec 24 were tagged locally. They came from a nearby place 7.5 kilometres away in South Lantau according to the information provided by the tagging group, the Global Change and Tropical Conservation Lab at The University of Hong Kong. One of the tagged butterflies has stayed in South Lantau for over a month, which indicates that different groups of various sizes of overwintering Danaids are strewn across the vast expanse of the woods apart from the two sites discovered by the green group, bespeaking the ecological significance of South Lantau.
Lo said South Lantau has been a popular overwintering or stopover site for migratory Danaids which flew from the north southwards every autumn and winter. But it is uncommon for two large swarms of Danaids visiting Hong Kong at the same period for longer than usual. The overall population of the overwintering Danaids in South Lantau is gauged to be in excess of ten thousand. He expected the Danaids to celebrate New Year in South Lantau and called on the public to abstain from disturbing them and move slowly when walking pass the butterflies to minimise air disturbance.
