The migratory butterflies form an important part of the ecosystem in the Western Ghats, which now stands to be disrupted.

Why have the migratory butterflies in the south stopped their journey this year
news Biodiversity Friday, December 02, 2016 - 11:44

Every year, as winter descends upon the eastern plains, thousands of butterflies gear for their annual migratory flight to the Western Ghats. One such journey they make is from Coorg in Karnataka to Aralam Wildlife Sanctuary in Kerala. However, even as December begins this year, there is no sign of the insects in the sanctuary.

While researchers and enthusiasts are worried, VC Balakrishnan, secretary of the Society for Environmental Education in Kerala, says that this may be because of the scant north-east monsoon. 

“Deforestation for so-called developmental activities may be the main reason behind rising temperatures, which could have affected the usual tour of the butterflies,” he adds. 

Species like Common Albatross, Lesser Gull, Great Orange Tip, as well as Danaine butterflies which travel in huge droves usually begin coming to the sanctuary November onward. On this journey, the butterflies traverse through the Nilgiri hills, Kottiyoor, Wayanad and New Amarambalam as well. The migration continues to happen till January.

Common Albatross (Photo courtesy SAP wildlife and Nature Photography)

However, this is not the first time the migratory butterflies are behind schedule. Balakrishnan recalls a similar delay which happened in 2011. The north-east monsoon also arrived late that year.

But why do these butterflies migrate at all?  

According to studies, one reason could be population outbreaks within one species, leading to a scarcity of plants and trees to host the eggs, says Srijita Ganguly, a research fellow at Kerala Forest Research Institute.

Butterflies are oviparous, meaning their eggs are laid with very little or no embryonic development inside the mother’s body and the eggs tend to become dormant if the weather is not suitable. â€śButterflies choose a larval host plant that would not only act as food for the larvae but also protect the eggs. When they do not find the right plant, they move on from the place,” she explains. 

Blue Tiger (Photo by Kingshuk Mondal via Wikimedia Commons) 

The lack of availability of food (flowering and nectaring plants) for adult butterflies could also be a factor, she adds. 

However, both Srijita and Balakrishnan say that it is difficult to pinpoint concrete reasons for migration. “The lack of migration can lead to a particular species becoming endemic to one area alone. And since butterflies are good biological indicators, this could be indicative to climate change patterns. However, given climate change cannot be measured over a short time, a longer observation period is needed to draw concrete conclusions,” explains Srijita.

Great Orange Tip (Photo by charlesjsharp via Wikimedia Commons)

Since they began surveying and documenting the migration 16 years ago, VC Balakrishnan and his team have seen an average of 15,000 - 20,000 Common Albatross butterflies per day during December and January.  

The migratory butterflies form an important part of the ecosystem in the Western Ghats, which now stands to be disrupted. 

A. Pavendhan, President of the Tamil Nadu Butterfly Society observes that because the north-east monsoon has been bare this year, the butterfly density is on the downfall in October and November. “This is the time when plants and trees are in full bloom here, so there is plenty of food for the insects, as well as butterflies. These insects also attract migratory birds, who feed on them,” he states.

Prabhakaran, an environmentalist studying butterfly migration in Coimbatore Forest Division, says that the butterflies also have an important role to play for the flora: their arrival makes possible pollination of various plants, ensuring a healthy ecosystem.

Lesser Gull (Photo by Jeevan Jose via Wikimedia Commons)

Prabhakaran explains that once the butterflies reproduce in the Western Ghats, it is the next generation which makes its way back to the eastern plains during March and April next year when the south-west monsoon picks up in the hills. He insists that there is a need to protect them. “As long as the native plants continue to be preserved, butterfly numbers will always be up. Chemical pesticides, insecticides as well as exotic plants should be reduced,” he says.

So far, no specific steps have been initiated by the government or government agencies to protect the butterflies or facilitate migration, Balakrishnan observes. 

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