by R. Nandini and Sanjay Sane

In popular folklore the appearance of certain birds is considered to herald the approaching rains. But there are other, less conspicuous, organisms whose arrival often goes unnoticed. Migratory insects of several species arrive in the thousands, either alone or in swarms, staggered across the days preceding the arrival of the rains.

In a recent paper that generated headlines worldwide, Globe Skimmer dragonflies Pantala flavescens (also called Wandering Gliders) were discovered to have the longest insect migration route recorded so far – a roundtrip flight between India and Africa with stopovers in the Maldives and the Seychelle islands.

Charles Anderson, reporting his findings in the Journal of Tropical Ecology <1>, recorded the arrival and departure of dragonflies in southern India, Maldives and West Africa over a period of fourteen years, with Malé, Maldives being the focal site. Dragonfly occurrence (particularly P. flavescens) in Malé began in October, peaking between November and December, coinciding with the east-bound high-altitude winds (~ 1000 m asl) of the Inter-Tropical Convergence Zone (ITCZ <2>).

Putting together dates of arrival across the study sites as well as the duration of residency of dragonflies at Malé, he reconstructs a steady north-south movement of dragonflies from southern India through the Maldives across 500-1000 km. A second wave of dragonflies was recorded in Malé between April and June, coinciding with occurrence of the Somali Jet, a band of fast low-lying southwesterly winds over the Arabian Sea blowing from Africa to India.

While this study was focused on dragonflies, Anderson also reports some information on birds, and found that the pattern of bird arrival in the Maldives mirrored that of the dragonflies, peaking between November and December. Among the bird species he reports as crossing the Western Indian Ocean are the Pied Cuckoo, Lesser Cuckoo, Eurasian Cuckoo and the Amur Falcon.

Collating available information on the migration of birds like the Amur Falcon, wind patterns like the ITCZ and Somali Jet, and records of occurrence of certain species of dragonflies at specific times of the year in the Maldives and India, Anderson hypothesizes that dragonflies, like some species of birds, possibly migrate in a loop from India over the Maldives and Seychelles to east Africa (Tanzania or Kenya) and then back again to India. The ITCZ is known to travel across the African continent, bringing rains to different parts of Africa over the year <3>, and insect, including dragonflies, are reported to migrate with these winds. Anderson suggests that, once in Africa, Globe Skimmers probably move southwards and then loop back north to equatorial east Africa before leaving the continent on the return migration to India.

In all, this incredible circuit would cover a total distance of 14,000-18,000 km, with 3,500 km over the open ocean, and would span possibly four generations of dragonflies.

How could insects only a few inches long undertake journeys that span their own body lengths several million times over? On the face of it, this implies deterministic and purposeful flying, as well as knowledge of which winds to harness to get to a destination. Anderson proposes instead that dragonflies need only rise upwards, encounter a passing wind and then largely soar or glide along this wind till they reach land. If this simple explanation is indeed the way in which dragonflies cover these enormous distances, how will such behaviour be affected by phenomena like global warming, which is known to alter the intensity and speeds of winds like the Somali Jet <4> and the ITCZ?

Dragonflies are reputed to be powerful fliers, and several species migrate long distances <5>. The Globe Skimmer is considered to be the most widespread dragonfly, occurring between the 40th parallels of latitude worldwide, and it is common across India <6>. Several populations of this species are known to migrate, and there are recorded migrations of Globe Skimmers from South America to Easter Island (possibly 3,600 km or more), to New Zealand (2,000 km), across the Chinese Bohai sea (nocturnal migrations) and over the Hindu Kush mountains (at altitudes of 6,500m asl). Within the Indian subcontinent, the Globe Skimmer arrives in Tamil Nadu after the North-East Monsoon, while in the western regions it arrives with the South-West monsoon, implying that there might be more than one migratory circuit even within this region.

While dragonflies and insects remain challenging to track over long distances, a number of studies have used arrival date information, mark-recapture techniques, and even radio-telemetry <7> to determine their migratory patterns. But, given the epic scale of the migration uncovered by Anderson, perhaps it would make sense to simultaneously examine both more visible taxa like birds and more populous taxa like insects. Doing so might provide a more comprehensive account of migratory patterns, mechanisms, and the evolutionary reasons for these spectacular journeys.

References

1. Anderson, R.C. 2009. Do dragonflies migrate across the western Indian Ocean? Journal of Tropical Ecology 25(4): 347-348. Download pdf.

2. The ITCZ is a weather system around the equator where the North-East and South-West trade winds converge. More information.

3. The ITZC in Africa. http://people.cas.sc.edu/carbone/modules/mods4car/africa-itcz/index.html

4. Meijing, L., Ke, F. and Huijun, W. 2008. Somali Jet Changes under the Global Warming. Acta Meterologica Sinica. 22 (4): 502-510. Download pdf.

5. Corbet, P. S. 1999. Dragonflies: Behavior and Ecology of Odonata. Cornell University Press, Ithaca.

6. Subramanian, K.A. 2005. Dragonflies and damselflies of peninsular India. A field guide. Edition 1.0. E-book of Project Lifescape, Centre for Ecological Sciences, Indian Institute of Science and Indian Academy of Sciences, Bangalore, India. 118 pages. Copyright K.A.Subramanian, 2005. Download pdf.

7. Wikelski, M., Moskowitz, D., Adelman, J.A., Cochran, J., Wilcove, D.S. and May. M.L. 2006. Simple rules guide dragonfly migration. Biology Letters, 2: 325-329. (Wikelski and colleagues radio-tagged 14 dragonflies in North America and followed them for 12 days with Cessna planes and ground teams.) Download pdf.

On The Other Side of Migration
By Kulbhushansingh Suryawanshi

Four months of meticulous notes on all the birds that I could see around my camp-site and my bird list was only EIGHTEEN! Winter months in the Trans-Himalayan region are a dream for the beginner bird-watcher. Unlike birding in the rainforest, where you are swamped by some 50-60 species who fly from tree to tree in an obvious attempt to make sure that you only get glimpses of them, birding in the Trans-Himalayas in the winter was a lot of fun. On the down-side it can get cold, very cold.

I study a mountain ungulate called the Blue Sheep (Pseudois nayaur) in Spiti, Himachal Pradesh and on the side I watch and keep notes on birds – mostly opportunistic sightings. For instance, once on a cold February morning when I opened the door to my base-camp I had a flock of Tibetan Snow-Finches rushing inside. I won’t blame them – it was -35° Celsius outside.

The Trans-Himalayas are not a great place for birds to hang out in the winter – and the species counts in winters hover around a twenty-two or so. But as spring approaches the place starts to change in more than one way. I had a chance to witness this winter to spring transformation in Spiti last year.

My first taste of spring was rather unpleasant – a fruit fly in my soup. The first obvious sign of approaching spring was not the appearance of any bird but actually the disappearance of one – the Alpine Accentor (Prunella collaris). As the days started to get warmer the Alpine Accentor disappeared from vicinity of the camp, but I kept seeing it higher up in the mountains at about 5000m till 1 March and that was the last I saw of the bird that winter.

My first real spring bird sighting was on 8 March when I went to the village of Kibber (4200m) to restock the camp provisions. There are two willow trees in the center of the village. As I walked past them I heard the familiar chirp of a House Sparrow (Passer domesticus). The common house sparrow migrates to lower altitudes during winter. Later in the day, as I was passing by a half-frozen stream that cuts across the village I was warmly greeted by the sharp Chi-chee-Chi-chee of the White Wagtail (Motacilla alba). A week later on 16 March I heard the village kids running around the camp shouting kakche-kakche; crow!!! But why were the kids so excited about the Jungle Crow (Corvus macrorhynchos)? Later, I found out that traditionally the crow is seen as a sign of the arrival of spring. I guess the White Wagtail and Sparrows are too small for them to notice or perhaps the early arrival of White Wagtail and Sparrow is a recent phenomenon.

Of all the species that were going to arrive with spring I was most excited about the Black Redstart (Phoenicurus ochrurus). This was the first migratory bird that I learned to identify. But I had to wait a bit longer. On 23 March I saw a Kestrel (Falco tinnunculus) sitting in a snow-hole as if it was just emerging out of winter hibernation den. A few other altitudinal migrants such as the European Goldfinch (Carduelis carduelis) and Fire-fronted Serin (Serinus pusillus) arrived in the first week of April. On 8 April came the Grey Wagtail (Motacilla cinerea). Unfortunately, I then had to return to the plains before the first Black Redstart arrived. Later a friend told me that they arrived on 6 May.

I was back in Spiti in September and I knew this time I would get to see who leaves when. But before they all flew off again I had some good sightings. First it was a Eurasian Sparrow-hawk (Accipiter nisus) hunting a Black Redstart, then a I saw a Spotted Dove (Streptopelia chinensis) on the streets of Kaza (3800m) and finally a Common Starling (Sturnus vulgaris) at 4400m. Meanwhile the Bluethroat (Luscina svecica) paid a transit visit.

And then it was time for the goodbyes. My last sighting of the Grey Wagtail that year was on 25 September. It had snowed some two feet that night but the morning was bright and the wagtail hopped around on the snow. The Black Redstarts were gone by the 15 October. October 21 was the last time I saw the White Wagtail that winter and by then the night temperature was already down to -5° Celsius. And then I was once more with my faithful eighteen friends.

The winter residents:
Golden Eagle, Himalayan Griffon, Lammergeier, Red-billed Chough, Yellow-billed Chough, Raven, Brandt’s Mountain Finch, Plain Mountain Finch, Tibetan Snow Finch, Alpine Accentor, Brown Accentor, Robin Accentor, White-winged Redstart, Great Rosefinch, Hill Pigeon, Himalayan Snowcock, Horned Lark, Wallcreeper