Bounteous rains this year is seeing the local butterfly population thrive, while the erratic nature of the monsoons is seeing the migratory ones largely stay away.
For the past five years, a team of dedicated ‘citizen scientists’, who founded the Bangalore Butterfly Club (BBC), have been scouring the urban forests of a growingly-congested city in search of the winged creatures. Impressively, the group maintains counts of the number of butterflies and species spotted on their three-hour walks done fortnightly in various parts of the city, as part of a study by the National Centre for Biological Sciences (NCBS).
While the final numbers and the study is yet to be published, the recorded observations allow a peek into the interesting relationship between the butterflies and the rains.
After three years of persistent decline in rains, heavy pre-monsoon showers this year in the city appears to have benefited the local butterfly population.
Management consultant and butterfly watcher, Rohit Girotra, who has been monitoring the population at Doraisanipalya Forest Research Plantations, notes that the native species has gone up this year — to more than 500 butterflies on average every walk —when compared to the past three years when barely 400 butterflies were seen.
“While we still have several more months to go, the initial numbers are encouraging. Butterfly numbers vary based on many factors, (but) rain does play a role given that survival of nectar and larval host plants through the year, which influences the butterfly population,” said Mr. Girotra.
What helps Doraisanipalya is ‘human intervention’, with the Forest Department and volunteers planting host plants that attract these butterflies. “But, for the population to increase, rains are required. In the summer, you could hardly spot a butterfly. We don’t know where they go, but if the rains are good, they are seen in abundance,” said Sanjay Mohan, Additional Principal Chief Conservator of Forests (Research and Utilisation).
Migratory species unseen
However, while the local populace might have thrived, migratory butterflies are yet to be seen. This is seen in Bangalore University, where the woods are relatively “untouched” - that is, no mass planting of host plants. While the local butterfly population remains stable, migratory butterfly counts have virtually crashed.
“From 2015, we haven’t seen any migratory swarms. These swarms would boost counts as more than 1,000 could be seen in three hours,” said Nitin R., one of the founders of BBC and an intern at NCBS.
Four species form the major migratory butterflies here: Dark Blue Tiger, Blue Tiger, Common Crow, and the Double Branded Crow. Lack of rainfall in the Western Ghats may be a sign of their disappearance here. “These butterflies start heading out of the Western Ghats when the monsoon showers hit in June. But, since there rains were delayed in June and July, they might have not migrated at all,” he said.
Rise in butterfly species
Despite the chaos marking the ‘development’ of the city, and erratic rainfall, the number of butterfly species being observed has steadily gone up.
In 2013, if 117 species were recorded at the Doraisanipalya forest research campus, the number has gone up over 130 species now, says the Bangalore Butterfly Club. The rare Clipper, for instance, that is found only in wet, evergreen forests was spotted for the first time in the city.
“These species could have come here as other nearby habitats may be affected, or if they are being accidentally introduced to the city. This also shows that our sampling efforts have increased, where we are spotting species not seen before...due to the good rains, we may even add 10 to 15 species to the list this year,” said Nitin R., a butterfly enthusiast.
