An arduous journey on vibrant wings

While documenting the butterflies of Nagarhole and Bandipur, researchers have uncovered the importance of migration for the survival of the species, writes Pavan Kumar H.

Just before the monsoon sets into the foothills of the Western Ghats, thousands of butterflies prepare to make their way to drier plains. Some of the migrating species include the dark blue tigress, double-branded black crow and Indian common crow. Over the next month, these colourful species travel over 400 km, passing by mountains and braving rough winds to reach the Eastern Ghats. 

The journey to the Eastern Ghats is essential for these butterflies. The eastern plains are climatically suitable as they are rain shadow areas between June and September. The butterflies who migrated spend their sunset days here. 

Butterfly

The migratory swarms typically consist of several thousands of individual butterflies. This annual migration is noteworthy for two reasons. Firstly, the migration takes place in response to the heavy downpour in the Western Ghats during monsoon. Secondly, the species of butterflies migrating from the Western Ghats do so longitudinally (from west to east) and not latitudinally (north to south).

While experts know where their journeys start and end, the route these species take to arrive at the eastern plains and back to the Western Ghats is still unclear. Any disturbance to the route will adversely impact their life cycles. 

Butterfly

Before the onset of the northeast monsoon, their progeny returns to the Western Ghats between October and early December. 

“To thermoregulate, these three species of butterflies migrate to the eastern plains to beat the rain,” says Santosh S, a faculty at the department of studies in zoology, Mysuru University. Along with V Gopi Krishna, president of the Nagarahole Conservation Society, Santosh has been conducting studies on these butterflies in Nagarahole and Bandipur Tiger Reserves. 

Butterfly

Over the last decade or so the duo have recorded the details of 209 butterflies in Nagarahole National Park and 185 species in Bandipur National Park. Apart from Nagarahole and Bandipur, the team intends to study the behaviour, adaptations and migration patterns in all five tiger reserves in Karnataka.

“There have been studies on butterflies encompassing the entire Western Ghats in general but this is the first area-specific study in Tiger Reserves of  Nagarahole and Bandipur including range and beat level information, along with GPS readings. There are hardly any such similar scientific studies being conducted in B R Hills, Bhadra and Kali Tiger Reserves,” says Gopi Krishna.

Butterfly

Ecosystem indicators

Butterflies are known to indicate the health of an ecosystem and play an important role in pollination. "Butterfly watching, coupled with scientific documenting and statistical analysis can be very helpful in staying alert about the subtle changes in habitat and climate,” says Brijesh Kumar Dikshit, Principal Chief Conservator of Forests, also an avid butterfly watcher. The number of species, their spatial distribution and count can provide important information about the habitat and its temporal change, he explains.  

However, disruption to their ecosystems and migratory routes has affected the survival of many species. The International Union for Conservation of Nature (IUCN), an international organisation working for nature conservation and sustainable use of natural resources, states that there are more than 18,000 species of butterflies in the world. India is home to 1,501 varieties. Experts so far have recorded the presence of 334 species of butterflies in the Western Ghats, a biodiversity hotspot.

Butterfly

Though butterflies live for a short period, their life is full of fascinating events. For instance, line blue retires to the shade by 9 am during the summer to avoid extreme heat and harsh sun. Krishna and Santosh are also mapping the presence of various species of butterflies in their habitats, the reasons for the presence of specific butterflies in those particular regions and the impact of development work. 

“Even the dust, smoke or residual smoke from minor construction could impact the larval host plants and nectar plants which are important drivers for migration. The absence of such supporting plants, which are cleared for such construction could adversely impact the lifecycle of butterflies,” says Gopi Krishna. He adds that any alteration to habitat that causes butterflies harm could have a cascading impact on human lives as well. 

Butterfly

“They are known to be  umbrella species and several plants that humans are dependent on, are pollinated by these insects,” he explains. 

Large-scale butterfly migration was last seen in 2018. Ever since, there has been a noticeable decrease in numbers due to varying monsoon patterns and climate change.

The researchers say their study can help the forest department assess the impact of projects and make crucial decisions regarding long-term conservation measures of a particular ecosystem. The impacts could include improving habitat connectivity and managing invasive species. Exhibits