Q&A with Dr Yuet Fung LING - Observing Climate Change Through the Lens of Butterflies

I earned my bachelor's degree in the HKU Faculty of Science, majoring in Environmental Science and Geography (Faculty of Social Sciences). While my undergraduate studies were less related to insects, I became increasingly interested in butterflies, as I always see these beautiful creatures during my hikes. I gradually developed a hobby of watching and photographing various butterfly species in Hong Kong, appreciating the rich biodiversity around this subtropical city. I later decided to pursue a PhD in butterfly and moth ecophysiology to investigate how these insects respond to climate and habitat changes. Now, as a postdoctoral researcher, I am expanding my research to explore the implications of these global changes on tropical insect communities.

My ultimate research interest is to understand the effects of global environmental changes (e.g., climate change, habitat change) on tropical insects. This is a big topic, so I have chosen to explore different aspects using various research techniques.

 

One of my projects used experimental techniques to understand the effects of seasonal morphs and starvation on the heat tolerance of a butterfly species. Heat tolerance, estimated by exposing organisms to a controlled high temperature in the lab, is commonly used in ecology to assess organismal responses under extreme heat conditions, which are expected to become more prevalent under climate change. Disruptions to temperature cues (which affect the seasonal morph of the butterfly) and food sources (which can result in starvation) can compound the effects of extreme heat under climate change. I therefore included these variables in the experiment to test for any interactive effects.

 

Another project examined how butterflies and moths regulate their body temperature during the day and at night to understand the strategies and challenges they face in coping with temperature variation in a subtropical climate. The results showed that day- and night-active insects use distinct thermoregulatory strategies and likely face different challenges in regulating body temperature as the global climate and forest canopy continue to change.

 

Species are also shifting their geographic ranges (e.g., to higher latitudes) under warming,  with some moving to higher latitudes as previously unsuitable habitats become favourable, and vice versa. One of my projects examined the range expansion of butterflies in Hong Kong, where multiple tropical species have been newly recorded over the past decade. I drew on a large Southeast Asian butterfly occurrence database compiled in our lab (by Eugene Yau, Emily Jones, and others) to calculate species temperature indices based on distribution patterns. These indices help track whether butterfly communities in Hong Kong are shifting towards more tropical species over time, using systematic long-term monitoring data collected in collaboration with the Fung Yuen Butterfly Reserve and the AFCD.

 

The project on butterfly migration (see Question 6) is less directly tied to global change, but still relevant. Some Danaid butterflies (e.g., the Crows) select only certain forested sites for winter aggregation, which may be vulnerable to threats from habitat changes, such as urban development and deforestation. Understanding their site use and behaviours is key to assessing their vulnerability.

Many surprising and unexpected results have come from the Danaid tagging project (see Question 6). The discovery of a Chestnut Tiger butterfly that migrated from Japan to Hong Kong was definitely one of the highlights. I also caught a Double-branded Crow during my fieldwork, a species that had not been seen in Hong Kong for 26 years. Apart from these rare species, there were other exciting moments: our team discovered new danaid aggregation sites in Hong Kong hosting thousands of butterflies in winter, and we recaptured or received reports of tagged butterflies moving within Hong Kong. These results are largely novel and unexpected, as prior research on danaids in Hong Kong has been very limited. I am glad these findings will contribute to a broader understanding of danaid ecology through future publications.

 

Besides the Danaid study, other projects have also brought unexpected results. For example, I was surprised to find that butterflies in my study species were not affected in terms of heat tolerance even after major temperature and starvation treatments. Further mechanistic and physiological investigations will be needed to understand this result, but the consistency in heat tolerance may suggest some resilience of the butterfly under environmental changes.

My latest research project is a butterfly migration study, using stickers to tag the wings of Danaid butterflies to track their movements in Hong Kong and nearby regions through recaptures and public reports.

 

Danaids (subfamily Danainae) are known for seasonal migration in other parts of the world. The most famous example is the monarch butterfly in North America, which migrates annually in the millions to Mexico and coastal California for the winter. In Hong Kong, large winter aggregations of thousands of danaids have long been observed, but little research has been done on whether they are migratory. Where do they come from? Where do they go?

 

Since winter 2021, our team, including Prof. Timothy Bonebrake, Emily Jones (PhD student in SBS), me, and a large group of volunteers, has been tagging Danaid butterflies across Hong Kong to understand their seasonal movements. We rely heavily on public reports of tagged butterflies, made possible by including our website address on the stickers.

 

This public collaboration greatly expands our data collection in both space and time, compared with having to recover the tagged butterflies ourselves. To reach a wider audience, we have also engaged in public education — from school visits and social media to hosting events and a symposium.

 

Our efforts have yielded good results - 15,918 tags over 4 years, 13 species of danaids tagged, 32 locations in Hong Kong visited, 1,503 recoveries (>50% reported by the public), and 78 movement records within Hong Kong. Although the local-scale movements don’t yet confirm regional migration patterns, they do show interspecific differences in movement directions, suggesting differences in overwintering strategies.

I was both shocked and excited. I couldn't believe I actually caught a butterfly that had flown all the way from Japan. Part of my excitement stemmed from knowing that a Chestnut Tiger butterfly had been recovered after migrating from Japan to Hong Kong in 2011. However, I assumed it was a rare event, as the species is more commonly known to migrate between Japan and Taiwan. It was also remarkable because the species is rarely seen in Hong Kong during winter; in fact, we hadn't recorded a single one during our field work over the past three winters. And most surprising of all, the discovery was unexpected, as none of the 15,000+ butterflies we tagged in Hong Kong had previously been reported outside the city. This was the first international movement detected in our study.

 

The discovery became even more special when I learned, after contacting the Japanese team that had tagged it, that this was the longest recorded migratory flight for the species. The straight-line distance from the tagging location in Fukushima to Hong Kong is 3,016 km, which is over 500km longer than the previous record. We are now preparing a manuscript to report the findings, so interested researchers and naturalists can learn more about the species and butterfly migration in Asia.   

Butterflies are an excellent study system for understanding climate change and conservation because they are highly sensitive to environmental conditions (e.g., temperatures and host plants are critical to their survival and fitness), their biology and taxonomy are relatively well studied compared to many other insects, and they are uniquely relatable to the public, making them ideal for education and outreach.  By studying butterflies, we can also gain insights into the responses of other insects, using them as umbrella species to guide conservation strategies.