There are numerous type of butterfly existing in Hong Kong, for now on, some, the main type of overwinter butterfly is Crows and Tigers (sub-family Danainae) with amount 1500, and approximate 10 known overwintering site are now existing in Hong Kong. Danaids are mainly gather in Sui Lang Shui to overwintering. The types of butterfly overwintering in Hong Kong include: Euploea core; E.midamus and some of the rare species like E.mulciber and Tirumala septentrionis etc. According to the scientific research from Agriculture, Fishers and Conservation Department, there are over 32000-45000 individuals spent overwintering in Hong Kong during 2002-2003.(Agriculture, Fisheries and Conservation Department, 2020) To concentrate one in Sui Lang Shui which is one of the main overwintering site of danaids, from 1999-2005, this 6 years are the peak period of overwintering danaids gathering with 4000-40000 danaids counted, than turn to a downward trend after 2005. According to the survey on overwintering danaids in 2009 and 2010, just 41 and 65 danaids counted respectively, just reached 1% of total number of danaids counted in the pass. (Green Power, 2020a) Thus, there are a upward trend in overwintering danaids visiting in 2011 for Sui Lang Shui with approximate 600 danaids counted. (Green Power, 2020)As same as Sui Lang Shui, there are the same trend in overwintering danaids in other sites like Deep Water Bay and Shing Mun Country Park.
On the other hand, to talk about the migratory, mainly, the most common overwinter butterflies danaids are come from the north side of Hong Kong, e.g. Northern China. In general, danaids will migrating to south in October (autumn) and migrating to north in February to March (spring) for each year.
The history variety trend of overwintering butterflies has been mentioned above, this is called range shifts, and the range shift can be influent by numerous factors include climate change, degradation of habitat etc. For the aspect of climate change, global warming is the international trend, a survey is elevated that thermal tolerance can be the factor to influent to the survival and distribution of species.(Tsun Fung Au and Timothy C Bonebrake, 2019) Global warming cause temperature rise can be case increase in range shifts of butterflies distribution due to the fact that butterfly larvae can’t condition own temperature, but also food ingestion and growth. So, butterfly species may migrate to find a place with lower average temperature. A butterfly watcher discovered a type of extremely rare butterfly species at Fung Yuen Butterfly Reserve called “Prosotas nora”, but Prosotas nora have migrated to the Hong Kong due to the fact that Hong Kong has experienced a long duration hot summer. Dr, Yau Wing-kwong, CEO of the Environmental Association said that rising temperature can attract new butterfly species but the original butterfly species that living in cities will be migration.(SOUTH CHINA MORNING POST, 2020). In addition, butterfly species like Prosotas nora mention above are common appear in south-east Asia and south Asia countries like India, Philippine, Malaysia etc. but the continue rising temperature force butterflies to north migration to find a cooler place to settle down. (Kara Rogers, )
In addition, degradation of habit is another range shifts factor to the distribution of butterflies, and even survival of butterflies. For example plant degradation, because butterflies have close relationship with plants and associate with plants by utilize one or other way Once introduce exotic to plant habitat like Mikania in Hong Kong, competition the original resource with the original plants, include light, water, food, breeding site and living space etc. Then disturb the ecological balance of original habitat by change the food chain and nutrient cycle, more original species will be suffer, plants diversity decrease follow by the plants suffer. This is the situation of habitat degradation. Butterflies are survival rely on original species plants to complete their life cycle, habitat degradation is an important factor to force butterflies to change the range shift.
About the habitat degradation in Hong Kong, not only introduce new species, some of the infrastructure project will also case habitat degradation. This situation were let environmental protection organizations to be worry, such as Tuen Mun Chek Lap Kok Link construction project, and Eastern Lantau artificial island project because the scope of construction site are near the existing butterfly habitat like Siu Leng Shui, North Lantau Country Park etc.(Green Power, 2016) the lowland and forest landscape will be urbanized after infrastructure build. Unavoidable, infrastructure construction are necessary to remove a large scale of landscape, the survival resource of butterfly and even the animal that mutualism with butterfly such as ant will disappear follow by the destroy of habitat, butterflies
Not only in Hong Kong, but also the mitigation pathway of butterfly. It is mansion that some kinds of butterfly in Hong Kong are come from southeast Asia. Southeast Asia butterfly habitats are also threat by habitat degradation, the main factor of habitat degradation of forest is deforestation. According to the IUCN, there are 47 kinds of insert were list as “Critically Endangered”, “Endangered” and “Vulnerable”, among 47 kinds of insert, 43 kinds of inserts are belongs to two butterfly families “Papilionidae” and “Nymphalidae”. This shows that the seriousness of threat that endangerment species that facing now by land use change include agriculture extinction and commercial deforestation. Because the sensitivity of butterflies to environment is high, so butterflies especially Nymphalide mention above must need to mitigation to find the situation habitat to escape extinction risk when habitat degradation. The extinction or migratory speed will be increase when the habitat degradation situation continue. For now on, butterflies belongs to Papilionidae family are migratory to Borneo, western Indonesia and eastern Indonesia from India, China, Thailand, Peninsular Malaysia.
Climate change and habitat degradation have close relationship with butterfly migration due to climate change will directly impact to the environment quality of habitat directly. Thus climate change and habitat degradation are not the independent factor, there are the linkage between this two factors: Climate factor is the key determine factor of habitat degradation. Global warming increase the rate of droughts, of habitat, extreme weather destroy the habitat landscape by flooding, wildfire etc. nature diester partly, case fragmentation and loss of habitat include forest , this is the main factor to decrease the survival ability and abundance because butterflies have a large extent on forest habitat relying to survival. Specific example like Argynnis adippe in UK, the coverage of landscape violet decrease, larva Argynnis adippe is extremely rely to violet that growth in warm microclimate, violet become the only hostplant of the Argynnis adippe’s larva. The other habitat of Argynnis adippe’s larva is Bracken litter/standing trash. Thus, in 2016, the coverage of violet in 5 locations in Morecambe Bay has been decrease by 50 % since 2004, Bracken litter/ standing trash has also decrease follow by the decrease of violet coverage. The foraging rate of Argynnis adippe’s larva under the unsuitable microclimate was decrease under the situation of continuous decrease in the coverage hostplant violet (Dr Sam Ellis, 2019)
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