Autumn butterfly migration in Hong Kong

[DocMartin]

After seeing some evidently migrant butterflies at Mai Po this past autumn, I’ve had some correspondence with Hong Kong Lepidopterists’ Society; perhaps of interest:

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Maybe of some interest that in autumn (sorry, don’t recall date; Oct or Nov) I saw maybe a hundred or so butterflies – danidae I believe – just on north side of border fence at Mai Po; they were in a place where the fence curves south, and several were flying against the fence, on southwest corner. Migrants I expect, caught by the fence, and trying to continue flights towards the southwest. What of Butterfly Valley near Kowloon reservoirs – still attracting gatherings, or maybe too much altered? (Any other gatherings known in Tai Mo Shan area? – I’m starting book on this and Kowloon Hills, for country parks; interesting if can mention that get migrant butterflies gathering, tho don’t need to give specifics re sites. Some winters ago, I saw fair numbers – maybe a few hundred in all – near north end of Shing Mun Res, as I recall just on/beside road towards Leadmine Pass.) Best regards, Martin Willliams

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Dear Martin, What you saw is indeed migrating Danidae. Our Society is monitoring this phenomenon for many years. The largest site is in Siu Nan Shui. The largest gathering we saw in the past is around 60,000. Sadly, the Tung Wah Hospital group is going to bulid a youth camp next to the site. We object to the proposal, but we have no way to stop them. Other sites boost much less in number. The Shing Mun is one of the site, but it seems that it is only a pit stop rather than a roosting site. One site is found in Deep Water Bay, it is the only site we know in HK island. Other sites are in the Lantau, mainly Fun Lau, Shui Hau, and the Shek Pik Reservoir. All the sites are tiny, mostly several thousands at most, but the species vary a bit from site to site. This year is a very bad year for the roosting butterfly. It seems to be the result of the dramatic change in weather for the past few weeks. If you have time, go to visit those sites next year, you will be amazed by the wonder of nature.

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Belatedly, many thanks for the prompt, full information re migrating butterflies. Could you please tell me where to find Siu Nan Shui? Very sad about the youth camp plans; I hope the hospital group will build carefully, so the site may remain intact. (Seems the Butterfly Valley near Lai Chi Kok is no longer of much importance thanks to developments.) Fan Lau seems not too sheltered; so I guess migrating butterflies gather there after heading southwest, then arriving at a sea crossing – maybe pause before continuing on across the sea (towards Hainan, eventually??) I watch birds, and birds sometimes do likewise; indeed, Fan Lau maybe also a place for migrant birds in autumn. Best regards, Martin

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Hi Martin Siu Nan Shui is an abandoned Dumping site with trees planted over it. It is monitored by the environmental department for methane gas. If you travel from Tuen Mun to Lung Ku Tan, it is near Lung Ku Tan on the right hand side of the highway. We are writing a report on the site this year. But as I said before, this year is a bad year and the report is not in favour of the roosting and offer no support for the objection to the building of the youth camp. The AFCD is doing the same thing. We don’t expect much retrun from our cooperation with mainland China since this is only the first year. We both lack man power and funding. Hope to do better next year.

see also: Hong Kong Lepidopterists Society Butterfly swarming in "Butterfly Valley" (pdf file; from HK Naturalist in 1930s)

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