Sunday, December 11, 2005

Flutter-by Migration

K. R. Kishen Das documents the amazing migration saga of butterflies

It is believed that the old name for butterfly was ‘flutterby’. However, another strong theory is that ‘butterfly’ originated from the old English word ‘buttorfleoge’, which means ‘milk thief’. The German ‘milchdieb’ for butterfly also means milk thief.

As a child, I would watch ants carrying food to their nest and track large groups of water birds long distances. Summer vacations at my grandfather’s farm were spent following large groups of grasshoppers, beetles and caterpillars, and watching as they devoured crops! Mass movements of birds, animals and insects have always fascinated me. As I grew older, I was wonderstruck by the dramatic migrations I would watch on television, including wildebeests in Africa, monarch butterflies in North America and desert locusts in Africa and birds across the globe. Today, what has me in its grip, of course, is the migration of our wonderful desi (homegrown) butterflies, particularly those of South India. These are ‘tigers’ and ‘crows’ and they migrate twice a year between the Western and Eastern Ghats, a most unusual route.

Lepidopterists recognise three distinct types of butterfly migration – short distance (local movement), long distance and dispersal (sporadic, random movement). I have observed all three types in South India. Oakleaf, emigrant, lime and albatross butterflies migrate short distances and can mainly be seen in the Western Ghats. Painted lady butterflies can be seen across India, and present the best-known example of dispersal migration. Some species of the family Danaidae, mainly in the Western Ghats, undertake amazing migrations for much longer distances of up to 500 km.

With my team, I have studied butterfly migration (mainly in and around Mysore) for five years now and our special interest is long distance migration. Initially, we had no idea where the butterflies around Mysore came from, or where they were headed. But after meticulous observation and by noting down dates and locations, a pattern emerged. We found that several species migrated along particular flyways at specific times of the year. Between March and April, migratory butterflies move in a southwest-to-northeast direction from the hills of the Western Ghats to the plains below and then upward to the Eastern Ghats. Few migrating swarms even make it to the Eastern Coasts. In September and October, they reverse this direction.
Interestingly, I often observed three species migrating together: the dark blue tiger Tirumala septentrionis, the double-banded crow Euploea sylvester and the common Indian crow Euploea core. Crows, predictably, are black in colour, while tigers have striped wings. Some tiger species such as the plain tiger Danaus chrysippus and the striped tiger are orange and black, like their feline namesakes. I also occasionally saw several other species migrating through the Mysore area – the lemon pansy Junonia lemonias, the blue tiger Tirumala limniace, the plain tiger and the common emigrant Catopsilia pomona.

Why do butterflies undertake long and clearly traumatic migrations? There are a number of possible reasons, of which the availability of habitats in which they can breed is clearly the most important. In South India, the extremely heavy rain of the Western Ghats monsoon makes breeding well nigh impossible and this probably triggers their move to the plains and to the Eastern Ghats. But when winter arrives these butterflies cannot survive in the open plains and scrub jungles and hence they move to the Western Ghats and enjoy the thick green cover. Also during summer, the lower plains turn very hot and host plants for butterflies, including many alkaloid plants, dry out. Unlike other butterfly species, the Danaidae do not undergo diapause (a sort of suspended animation when no growth occurs) and this probably inspires them to spend their summers at the Western Ghats, which offers lush and green vistas.

These migrations can be seen in cities such as Bangalore, Tumkur, Mandya, Mysore, Chamrajnagar, Virajapete, Madikeri, Palakkad, Coimbatore, Ooty, Kannur, Vellore, Chennai, Tirupathi, Salem, Dharmapuri, Dindgul, Kodaikanal and Protected Areas like Sri Venkateswara Sanctuary and National Park, Horsely Hills, Jawadi Hills, Nandi Hills, Bannerghatta National Park, Melukote Temple Sanctuary, Bandipur, Waynad, Mudumalai, Upper Bhavani, Nagarahole, Brahmagiri Wildlife Sanctuary, Chinnar Wildlife Sanctuary, Valparai, Topslip, Annamalai, etc.

As with most species, in the case of butterflies too, the urge to migrate is probably thanks to a combination of climatic conditions and food availability. But this area of natural history is so little studied. We need considerably more data to develop a clearer understanding of the incredible long distance butterfly migration of south India.

Whatever the reason, the behaviour of these flying jewels during their migrations is utterly fascinating. For starters, how does one know if a group of butterflies is migrating or not? To begin with, the clusters give them away. When you see hundreds, sometimes thousands of blue and black butterflies moving in loose flocks (roughly southwest to northeast in March/April and northeast to southwest in September/October) you can be sure you are witnessing a migration. And, rooted to one spot, you may be able to watch the phenomenon for hours. In the Western and Eastern Ghats, this is most likely to be on a sunny day, with a sky studded with high-level cirrocumulus clouds appearing as thin white patches or layers without shading.

Our observations suggest that butterflies start their daily expeditions around 9 a.m., choosing to settle down to rest around
3 to 4 p.m. Much, of course, depends on the weather. Naturalists confirm that butterflies may break journey in a given area for as long as three to five days. But heavy rain could cause such halts to be extended to weeks. The butterflies we observed typically took between one and two months to migrate the 300-500 km. between destinations. During the April 2005 migration, I observed butterflies settling in Bangalore all the way to July because of the exceptionally heavy rains, which even brought the bustling metropolis to a halt.

Apart from migration, butterflies have a whole array of fascinating behaviour to keep naturalists absorbed, including ‘mud-puddling’, basking, feeding, mating and breeding. Like birds, butterflies can often be seen basking in the sun, wings spread wide. In many butterfly species, only males mud-puddle, but in migratory species such as tigers and crows, both sexes engage in this activity, in which the insects alight on wet mud and suck up salt and other minerals and nutrients.

Tigers and crows usually mate as they congregate along their migration route. I have often observed males ‘carrying’ females along with them. The female to male sex ratio of migrating tiger butterflies is approximately 1:3. It is difficult to distinguish the sex of crows. The ratio of crows to tigers is also 1:3.

Tiger and crow butterflies need pyrrolizidine alkaloids for the production of sexual pheromones and these they obtain from Crotalaria and Heliotropium plants. Breeding usually takes place in the months of February and August. Both species lay eggs on milkweed plants, preferring Tylophora indica and Wattakaka volubilis over others.

Since we had initially identified four species, we assumed that they all migrate together. But we soon realised that only three species migrate, with the blue tigers temporarily joining the congregation, for reasons we have been unable to fathom. In the plains, we also saw a few resident common Indian crow butterflies that do not participate in the mass migration.

Sanctuary readers can help us keep track of the phenomenon of butterfly migration by keeping a watchful eye on the silent flocks. All too often, we see ‘processions’ flitting past but probably never give them a second glance or thought. Consider for a moment the sheer grit of millions of butterflies travelling 300 to 500 km. each way, each year. They expend colossal amounts of energy and without huge internal storage systems in their bodies, they must obviously replenish expended energy frequently. For this, they must visit flowering plants from which to suck nectar. Just imagine the incredible pollinating job they do, visiting literally billions of flowers of various species across a wide swathe of country.

Additionally, migrating tigers and crows play an important part in the food chain, since many birds, spiders, reptiles, amphibians and small mammals that inhabit their migratory path feed on these butterflies. These delicate creatures are also preyed on by rodents, and toads, particularly when they ‘mud-puddle’.

No one has really even estimated the sheer numbers that are trapped in spider webs, or are eaten by bulbuls, mynas, bee-eaters, flycatchers and other avian predators. Butterflies have survived this gauntlet of threats over millions of years, but today they are faced with a threat they may not be able to tackle – us.

Humans constitute an overwhelming threat to butterflies, primarily because we are destroying their natural habitats and spewing lethal toxins into their food sources. Additionally, migrating tigers and crows die in thousands each year as they negotiate highways where fast-moving vehicles take a hideous toll. While we sit up and take notice of the effect of mining, urbanisation, industrialisation, deforestation and encroachments on species such as tigers and elephants, we hardly spare a thought for the impact on migrating butterflies depending upon plants to feed, breed and to seek shelter from harsh weather.

Virtually anyone can be a part of a growing network of sensitive individuals who seek to understand butterfly migration by carefully observing and cataloguing their annual passage and behaviour. This work is important not just to the well being of butterflies, but for conservation efforts on a larger canvas because such efforts can contribute to habitat protection.
Butterfly migration maps could plot forest stretches and natural resources needed by insects and these habitats could be singled out for special conservation so as to aid sustained migrations. Even simple steps, such as promoting organic agriculture along butterfly routes, encouraging the growth of suitable wild host plants and alerting motorists to the vulnerability of butterfly flocks to danger from high speeds could go a long way in providing these miraculous survivors with the edge they need.

Sanctuary readers are requested to contact us when they see a large number of butterflies anywhere in South India. Even more valuable, (if you have the time and the inclination), you can help us conduct butterfly counts. This involves counting the number of butterflies across a width of 25 m. over a 15 minute time span. There are many more guidelines that we can provide to readers and we look forward to working with you in defence of butterflies. You never know, a migratory butterfly breeding ground might be awaiting discovery right now in your own backyard.



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