Butterflies are considered as bio-indicators of climate change. Cementing the argument, butterfly observers in Tamil Nadu have observed a strong correlation between healthy butterfly migration and good rainy season that follow immediately.
According to The Nature and Butterfly Society (TNBS), Tamil Nadu witnessed reasonably good migration of butterflies from the Western Ghats hill ranges to the plains and the Eastern Ghats in April and May this year, which was followed by good pre-monsoon rainfall across the State in the summer.
Butterflies belonging to the Danainae sub-family called ‘Tigers and Crows’, such as Blue Tiger, Dark Blue Tiger, Double-branded Crow, and Common Crow, migrate from the Western Ghats towards the Eastern Ghats from mid-April to May, before the onset of the Southwest Monsoon. Active migration of Tigers and Crows was observed in Tamil Nadu, especially over the western districts of the State, from mid-April this year.
“TNBS has been observing the correlation between the migration and rains for the last several years. This is an observation by butterfly enthusiasts. However, a systematic and scientific study is needed to establish this correlation and publish the findings as a paper,” said Pavendhan A., a senior member of TNBS.
As per observations made by TNBS since 2013, no butterfly migration was reported in 2016 when Tamil Nadu witnessed a drought-like situation. Though the migration improved in 2017 and 2018, there was a decline in 2019. TNBS considers this year’s migration ahead of Southwest Monsoon a healthier one compared to the ones in the past few years.
Butterflies belonging to Danainae subfamily in the Anamalai hills near Coimbatore. | Photo Credit: SPECIAL ARRANGEMENT
The annual phenomenon this year started from April 14, with the movement of Crows and Blues observed at a rate of 25-30 individuals per minute, flying from southwest direction to northeast direction. The movement was active between 8 a.m. and 1 p.m.
According to TNBS, butterflies moved towards Tiruppur, Erode and Sathyamangalam during observations made at Pollachi and several parts of Coimbatore city.
Observations from Kotagiri in the Nilgiris also showed mass movement of butterflies towards Sathyamangalam. A burst of butterflies was observed over Tiruppur on May 11.
“Interestingly, movement was not observed in some regular paths in Coimbatore, including the Siruvani hillside and Maruthamalai. However, the migration was active via Anaikatti,” said TNBS member Ramanasaran H.
Observations made in Tiruppur also showed that butterflies moved en masse towards Sathyamangalam, said TNBS member from Tiruppur Gopalakrishnan S.
Observations over the years have indicated that the April-May migration count is always lower in scale, compared to the pre-winter migration or reverse migration from Eastern Ghats to the Western Ghats in September and October, ahead of the Northeast Monsoon.
