A total of 13 Danaid species have been recorded in Hong Kong. All except the Plain Tiger have the habit of overwintering in groups. There are three main groups of overwintering Danaids in Hong Kong: crows, tigers (excluding Common Tigers), and Common Tigers. From October to November each year, local Danaid populations rapidly increase. Many come from regions north of Hong Kong, migrating south in October to find a warm overwintering site. They return to the north in February to March the following year, or may reproduce in the overwintering site.
In Hong Kong, there are about 10 known overwintering sites for Danaids. These sites are often densely wooded, providing habitats and shelter from wind and rain. Water supplies such as perennial streams are also present at the overwintering sites. Siu Lang Shui, Tuen Mun, is the largest known overwintering site for Danaids in Hong Kong; during the peak period in recent years, about 40,000 overwintering Danaids were recorded.
In 2009, we have launched an Overwintering Danaids Survey; the surveyed sites included Siu Lang Shui, Shing Mun Country Park and Deep Water Bay. It aims to collect more data on overwintering Danaids, including the distribution of local overwintering sites, migration routes of overwintering Danaids, statistics on and behaviour of local overwintering Danaids. In the future, we will expand the survey by collecting data from more overwintering sites, in order to explore the wonder of nature and safeguard these sites from destruction.