Butterfly migration: Blue tigers head towards Western Ghats with the onset of North-East monsoon

It is Ayudha Pooja day and Tiruchy Road in Coimbatore is at its busiest. Even as makeshift shops selling flowers and puffed rice do brisk business, in the skies above, something magical unfolds. We first spot them here and there: blue tiger and dark blue tiger butterflies, and a few common crows float above us. Soon, there are more. They seem to be everywhere. That is when we realise we are right on the migratory route of lakhs and lakhs of butterflies flying from the Eastern Ghats towards the Western Ghats to escape the North-East monsoon that is battering Chennai and its surrounding districts.

Butterfly watchers in cities along their path are on high alert. This is the moment they have been waiting for all year. Alerts on the WhatsApp group Butterfly Migration India invite men and women in places such as Salem, Erode, Tiruppur, Coimbatore, and Madurai, apart from Kerala, to step outside and count the butterflies.

According to CV Nishanth, a core member of The Nature and Butterfly Society (TNBS) that was started as a Facebook group in 2013, some places in Coimbatore recorded as many as 100 to 120 individuals per minute. “There are blue and dark blue tigers, common and double banded crows, and a few emigrants,” he says. “In Kalapatty main road, 120 individuals were spotted per minute at 9.50am on October 18.” Nishanth says that they undertake this tedious journey to escape the rains and reach host plants in the forests of the Western Ghats.

Why do they travel all the way?

Dr Kalesh Sadasivan, a research associate with the Travancore Nature History Society and a member with the State Board for Wildlife, Kerala, says that once they make it to deep forest, they start a new chapter in life. “These butterflies start their journey after the pre-monsoon showers in the Eastern Ghats, flying past Tamil Nadu plains and the Mysore plateau,” he says. Once they reach their host plants, they feed, then mate. “After they lay eggs, they die,” he says.

To travel hundreds of kilometres only to perish? “Their subsequent generations — we don’t know which ones, perhaps the third or fourth — fly back to the Eastern Ghats around May when the pre-monsoon showers ahead of the South-West monsoon arrive,” he explains. The most fascinating aspect of this up and down journey, Dr Kalesh says, is the in-between months, when they wait for “environmental cues” at forest patches where there is plenty of food.  

“Millions of them congregate on trees from January to February, simply waiting,” he says. They know it in their DNA when the time is right to fly back. Dr Kalesh, who has been part of several Forest Department surveys, has witnessed such large swathes of butterflies in the forests of Parambikulam. “They are fascinating to look at,” he recalls

A Pavendan, the founder and president of TNBS too has seen such massive butterfly congregations in Silent Valley in Kerala. “Entire trees will be covered inch to inch,” he says. As part of the TNBS, he has contributed to several Forest Department surveys and studies on butterflies and has been observing them since 2011. The migration, he says, takes place when skies are clear with very little cloud cover. “They don’t fly continuously,” he adds: “They settle down on trees by 3pm to rest, flying back the next morning.”

The sheer magnitude of the butterflies can take one’s breath away. Picture this: Pavendan says that when there is enough sunshine, around 100 individuals can be seen within a 50 to 100 metre distance. “So, 6,000 of them cross the same distance in an hour,” he says. While their flight pattern is scattered, if people looked up, they are sure to notice the delicate creatures, he adds.

But in our crowded cities with life moving at top speed, not many have the curiosity to do so. Those who do, follow the butterflies’ journey closely, aiding in scientific data collection. “Butterflies are an indicator of a healthy eco-system,” says Pavendan. “They hold an important position in the food chain; in every stage, right from eggs to caterpillars, they are a food source to several species, such as spiders and birds.”

TNBS has come up with a checklist documenting 329 butterfly species in Tamil Nadu, also contributing the baseline data for Sathyamangalam Tiger Reserve. Documenting butterflies is not like bird watching, says Pavendan. The task requires a keen eye, and more than anything, a steady love for the insects that requires one to patiently squint into the skies.