Saving Taiwan’s Crow Butterflies


2016 / January

Kuo Han-chen /photos courtesy of Hsu Ching-ho /tr. by David Mayer

“Thousands of crow butterflies

Flap their resilient wings

In a three-day aerial parade

Undulating forward across hill and dale.”

—Tseng Kuei-hai, “Wintertime Festival of the Crow Butterflies”

The above lines are a description of the habitat of Taiwan’s crow butterflies, penned by the noted poet ­Tseng Kuei-hai in celebration of the annual migration of the butterflies, which move in prodigious numbers each year from north to south, and then back again a few months later. However, the heavy hand of climate change has been swatting away at the crow butterflies in recent years.

Purple river

Maolin District is located 58 kilometers to the northeast of downtown Kao­hsiung in a largely undeveloped area of virgin forest traversed by the Zhuo­kou River and punctuated by high peaks, waterfalls, and valleys. Most of the residents in this district are from the indigenous Ru­kai tribe, well known for its distinctive stone slab houses. The butterfly valleys here, regarded as world-class eco-landscapes, are where Taiwan’s crow butterflies head to spend the winter.

“Perhaps because crow butterflies have always been such a common sight,” says Ru­kai tribe member Chen Yizhen, “we Ru­kai folk have always felt a bit ho-hum about them. It wasn’t till their numbers suddenly dropped in the past few years that we finally realized how precious they are.”

Crow butterflies belong to the genus Eu­ploea in the subfamily Da­na­inae, the milkweed butterflies. Ranging from medium to large in size, they have a wingspan of four to eight centimeters. They breed from spring through summer throughout Taiwan, but congregate in winter in the warm climate of southern Taiwan. Mao­lin District in Kao­hsiung is one of their main wintering grounds.

Noted lepidopterist Chan Chia-lung explains that there are four species of crow butterfly in Taiwan: the striped blue crow (Euploea mulciber); the blue-banded king crow (E. eunice); the double-branded crow (E. sylvester); and the dwarf crow (E. tulliolus). Like all moths and butterflies, their wings are covered with minute scales, such that sunlight reflecting off the scales will produce a sheen in various shades of purple, depending on the angle of the light. Japanese entomologists have coined a special noun—magic light—to describe the color thrown off by crow butterfly wings.

Scholars have identified at least three stages of the annual crow butterfly migration cycle. The first stage occurs in March and early April, when the butterflies move north. Then in May through early June, a new generation of young butterflies just emerged from pupae undertake a secondary migration. And in early to mid-October, crow butterflies begin migrating en masse to the south, covering hundreds of kilometers on their trip in an airborne spectacle that has been dubbed “the butterfly highway.”

Butterfly watching activities in Mao­lin run from November (after the butterflies have arrived for the winter) through the following March. At the height of the migration, as many as 10,000 crow butterflies per minute can be observed flying along at very high speed, creating a virtual river of purple light. It is a truly stunning sight.

Sharp drop in numbers

“When I was a kid,” says Mao­lin old-timer Chen ­Sheng, “I often saw huge swarms of crow butterflies that practically filled the sky. It was breathtaking.” He also recalls riding his bicycle to school and falling after slipping on butterflies.

As early as the 1960s, scientists conducted field surveys in Mao­lin and found that at times the butterflies in the valleys there could number up to 2 or 3 million. Mao­lin ranks, along with the valleys in Mexico where many monarch butterflies winter, as one of the two largest butterfly wintering sites in the world. However, the number of butterflies wintering each year in Mao­lin has dropped off sharply due to the destruction of habitats and the impact of extreme weather.

Chan Chia-lung notes that the number of crow butterflies in southern Taiwan now peaks at about 600,000. In the valleys of Mao­lin, this number is down to about 100,000 to 200,000; in an earlier time, by contrast, up to a million could be observed there. These figures show that if we don’t show a greater sense of urgency in our conservation efforts, this lepidopteran miracle of Taiwan’s might one day be no more.

The biggest single cause of the butterflies’ disappearance is habitat destruction. Whereas their migration route used to steer them well clear of human activity, much new land has now been cleared for agriculture, and the butterflies have to get across more roads and freeways than ever before. In 2007, Chan discovered that many of the butterflies returning north in the spring were being killed or injured after getting caught up in the powerful vortices created by cars traveling at high speed along Taiwan’s freeways.

Making way for the butterflies

Chan got together with Cheng Juey-fu and Lin Tie-­shyong (associate professors in the Department of Civil and Ecological Engineering at I-Shou University) and contacted the National Freeway Bureau to suggest that protective netting be put up along selected stretches of freeway to help the butterflies get safely over the hurdles. Their suggestion was accepted.

During the northward migration (early March through Tomb Sweeping Day on April 5), the highway authorities work together with environmental groups to put up protective netting, when the butterfly traffic merits it, along National Freeway No. 3 at the 252 kilometer marker, and when the butterflies are especially numerous they further close a 500-meter stretch of the outside lane to make sure the butterflies get across.

Taiwan’s efforts to protect the crow butterflies have attracted international attention, and even featured in programs on National Geographic Channel and Discovery Channel. Every time Chan has gone overseas in recent years to take part in environmental activities, foreigners never fail to tell him of their high regard for what Taiwan has been doing for ecological preservation.

Inspired by Chan, a group of indigenous residents in Mao­lin formed the Kao­hsiung City Mao­lin District Crow Butterfly Preservation Association.

In addition to habitat destruction, another thing the association is especially worried about is climate extremes, which have become much worse in the past year or two.

Tang Xiong­jin, of the preservation association, explains that Taiwan’s climate has become quite hot, causing some plants to flower at odd times, sometimes leaving butterflies, which depend on nectar as their main food source, without their normal fare available. In addition, water sources have dried up considerably this year. Butterflies don’t usually go foraging for water until January, but they’ve recently been appearing at the mouth of the Zhuo­kou River on precisely that errand. The association is monitoring the situation closely to see whether it will cause a big drop in butterfly populations.

To preserve crow butterfly populations, reports Tang, the association last year leased a mountain valley from the forest authorities and built a footpath and ecopark for visitors interested in butterfly watching. The idea is to get more people interested in and committed to the protection of butterflies. In addition to the leased valley, Mao­lin District has seven or eight other mountain valleys where authorities carefully limit the number of vehicles allowed to enter.

Eco-friendly farming

Apart from active efforts by environmental groups to protect the butterflies, various social groups and farmers are also getting into eco-friendly farming as a means of improving butterfly habitats, and support for these efforts is beginning to grow. Crow butterflies need nectar plants. Mango flowers, for example, are an important food source for them as they migrate northward in the spring, but farmers have long used chemicals to keep pests away from their mango trees, and this practice has been detrimental to the survival of crow butterflies.

Su Muh-rong, chief executive officer of the Tse-Xin Organic Agriculture Foundation (TOAF), explains that his organization has been promoting butterfly-friendly farming techniques in the hills of Mao­lin since 2012. In the first year they encouraged farmers to cut down on the use of agricultural chemicals at least to the point where fruits dropping from trees would be free of residues. At the beginning six farmers responded to the call, and this year the number of participants is up to 13. Among them, five farmers have abandoned agrochemicals completely and received certificates from the Forestry Bureau in recognition of their contribution to environmental conservation.

TOAF has helped farmers enter into supplier contracts with Lee­zen Company, which runs a chain of organic food shops throughout Taiwan and has used the mangoes supplied by these farmers to develop a variety of organic products, including unripe mangoes, dried native mango, and “lovers’ fruit” popsicles (i.e. popsicles laden with bits and pieces of unripe native mango). This approach makes for a happy modus vivendi between humans and butterflies. Su says that TOAF encourages farmers to cultivate nectar plants all around their mango trees as a food source for adult crow butterflies.

The push for butterfly-friendly farming met with strong resistance at first. Chen Yi­zhen, deputy chair of the Mao­lin District Council, acknowledges that reducing or abandoning the use of agrochemicals will cause production to drop, but feels it’s worth it in order to protect the crow butterflies, which is why she is vigorously promoting it. She expects that 21 farmers will be practicing the new techniques next year.

Butterfly defense brigade

Crow butterflies live in Taiwan’s flatlands up to an altitude of 500 meters. Pretty much anywhere that humans can live, so can the crow butterflies, so they serve as a pretty good benchmark for environmental quality. Chan points out that Taiwan originally had five species of crow butterfly, but only four remain now; the Taiwan large crow (Euploea phaenareta juvia) is the first species of butterfly ever to disappear from Taiwan.

Chan stresses that visitors to Mao­lin must not shake trees or throw stones while the crow butterflies are wintering there, so as not to disturb their rhythms. In addition to supporting butterfly-friendly farming, members of the public can also help by cultivating more nectar plants at home.

Preparing to leave Mao­lin, we take a last look at a cloud of crow butterflies as they flutter about the plants and shrubbery before disappearing into the forest. The undulating sheen of purple in motion is a sight we won’t soon forget.

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