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Tuesday, November 24, 2020

An early butterfly migration that holds signals of climate change

The journeys that butterflies take to get to more favourable weather may hold the answers to pressing environmental questions.

Written by Nithya Pandian , Edited by Shruti Sundar Ray | Updated: October 22, 2020 8:52:58 pm
Dark Blue Tiger butterflies collecting nectar from a flower. (Photographed by Jeswin Kingsly)

An unusual phenomenon took place in late August, this year—thousands of butterflies could be seen travelling from the Eastern Ghats to the Western Ghats. A record 1060 butterflies were found to be migrating from one hill complex to another, in a single hour, on August 25.

The movement itself was not unusual—but the timing was.

Every year, two seasonal butterfly migrations occur between the Western and Eastern Ghats of the Indian peninsula in search of food and survival.

Intense rain in the Western Ghats complex during the southwest monsoon makes it difficult for the butterflies to survive. To avoid the inclement weather, butterflies start their first migration in May and June (before the onset of southwest monsoon) from the Western Ghats to the plains and to the Eastern Ghats.

During the southwest monsoon, Eastern Ghats provide the ideal climate for the butterflies to survive. The migratory adults become reproductive, breed, lay eggs, and die. The successive generation starts to migrate back from the Eastern Ghats in late September and October (before the onset of the northeast monsoon, which brings rainfall to the Eastern Ghats). This is the second seasonal migration of the year.

But this year was different. “This year, after a gap of eight years, early migration took place. The migratory butterflies started to travel back to the Western Ghats between the last week of August and September middle,” said A Pavendhan, president of The Nature and Butterfly Society (TNBS), over a phone call with indianexpress.com.

Why? The second migration took place early this year due to heavy rainfall in the Eastern Ghats during the southwest monsoon. The butterfly offspring population would not have been able to survive in the Eastern Ghats with unviable weather conditions and a lack of food, forcing an early migration.

Butterflies are bioindicators, and the early migration means an early arrival of monsoon. With climate change altering weather phenomena across the world, tracking and studying seasonal butterfly migrations have assumed greater significance.

Crimson Rose butterfly. (Photographed by Jeswin Kingsly)

Butterfly species have their own unique routes

According to TNBS, out of 316 validated species of butterflies in the region, only 20–30 species migrate. “Dark blue tiger, blue tiger, common crow, and double branded crow are the common migratory butterflies between the Ghats,” said Pavendhan.

The butterflies originate from Western Ghats ranges, such as Kodagu, Wayanad, Nilgiris, Siruvani and Anamalai, and move toward the Eastern Ghats consisting Yercaud, Pachamalai, Kolli, and Kalvarayan hills during the first migration. And back, for the second migration.

Pavendhan explained: “Each group of species would congregate and use a specific path to travel back and forth to complete the cycle. For instance, butterflies migrating from the Yercaud would reach the Anamalai hills by traveling through Nilgiris, Coimbatore, Pollachi, and Anamalai. Butterflies from other areas of Eastern Ghats use different passages to return.”

In the mountains, butterflies usually fly 10–20 km per day. In the plains, using the wind, they can fly 50 km per day. It takes some butterfly species around four to five weeks to cover the distance between the Ghats.

The Nilgiris are one hub for the migratory butterflies. “During the same time period, lakhs and lakhs of butterflies fly through the Nilgiri hills from the Kallaru corridor and Thengumorahada,” said Manoj Sethumadhavan, trustee of Wynter Blyth Association (WBA). “The Nilgiris have more roosting and congregating places, and hosting trees for these butterflies.”

TNBS identifies Coimbatore—home to 276 butterfly species—as the top butterfly hotspot in Tamil Nadu. “The district has sholas, dried grasslands, wetlands, thick forests, and adequate weather conditions for the butterflies to live,” said Pavendhan.

Dark Blue Tiger, Blue Tiger and Common Crow congregation at Amrita University. Special arrangement, picture courtesy TNBS

The migration between the Ghats is a form of local migration but other types of migration are also prevalent among butterfly species in the hills of peninsular India.

“Altitude migration happens in Coorg. The Common Albatross is one of the high-altitude migrator species that travels from the high hills of Coorg to Aaralam Wildlife Sanctuary through Wayanad, navigating the Cheenkanni Puzha river line between November and February,” explained Kalesh Sadasivan, a plastic surgeon and one of the founders of Travancore Natural History Society (TNHS).

Another migration pattern is transnational. For instance, the Crimson Rose species travels from southern India to Sri Lanka.

Enthusiasts are filling the gaps in butterfly data

“In the British era, there were records of butterfly migration. But post-independence, people have shown no interest in this event,” said Sethumadhavan. “Now, we started to notice the small but significant changes in climate and butterfly migration. We record it for the next generation to research further.”

WBA, the association that Sethumadhavan is a trustee of, conducts butterfly walks and butterfly census in Nilgiris at regular intervals with the help of the forest department. Last year, members from the group recorded a rare sighting of the Dark Pierrot and the Pointed Lineblue butterfly in Kotagiri slopes. The Dark Pierrot had last been sighted in Kotagiri in 1978.

Butterfly enthusiasts have now taken up the task of recording the butterfly migrations and also organises regular searches. TNBS volunteers have successfully found and revalidated 316 butterfly species in Tamil Nadu.

“When we started to make the checklist a decade back, we had no idea about the species and no data available. Local dwellers would tell us the time, season, and other valuable information about these beautiful beings,” said TNBS president Pavendhan. “We thought we should collect data on butterflies in South India. After 10 years, now, we have enormous amounts of data.”

Congregation of butterflies. Special arrangement, picture courtesy TNBS.

Apart from recording butterfly migration, TNBS members have also been involved in environmental research activities such as butterfly surveys, hotspot identification, technical studies on the butterfly life cycle, and studies on host and nectar plants that butterflies rely on.

Another initiative that connects like-minded butterfly enthusiasts through a WhatsApp group is the Butterfly Migration India (BMI) forum. During the migration, people along the migratory path watch, record the event and send details on the WhatsApp group about the number of butterflies, flying direction, type of butterflies, and so on. BMI volunteers working on one zone alert those from the next zone.

“For instance, if a volunteer watched tiger (tiger butterfly) migration in Palakkad Gap, he/she would alert the volunteers in Coimbatore,” explained Sadasivan, who also participates in the BMI group. He added, “From 2016, nearly 200 volunteers from various parts of the South Indian states have joined this group. 20 smaller NGO teams are also working with BMI to record South Indian butterfly migration data.”

Need for more research into butterfly migrations

“The sad thing is, people in India who knew about Monarch migration happening in Mexico have no idea about butterfly migration happening in their backyard,” said Sadasivan.

Several research studies in Europe and North America have suggested a correlation between climate change and changes in population distribution of butterfly species. Butterfly behaviour is an indicator of the health of the ecosystem—some researchers have studied climate adaptations in butterflies to better understand the impact of climate change on ecosystems.

Butterflies engage in mud puddling after rains to seek out nutrients in moist mud and plant matter. Picture courtesy TNBS.

In the Western and Eastern Ghats, it is clear that altered rain patterns have affected the migration patterns of butterflies. Despite this, butterfly migration is not well-studied in India. There is a growing need for institutional efforts to collect data and conduct research on these bioindicator species.

According to Jeswin Kingsly, head naturalist of Kipling Camp at Kanha Tiger Reserve, who is also a member of TNBS, “The Kerala forest department has so many initiatives to record the behaviours of frogs, snakes, and even dragonflies. Tamil Nadu forest department takes a survey on big cats and pachyderms. They should start initiatives to record the data for butterfly species too.”

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