World Migratory Bird Day :

Ruffled feathers

Sajitha Prematunge

Colombo University Zoology Department Head Prof Sarath Kotagama. Picture by Nissanka Wijerathne

National Bird Ringing Programme conducted by the Field Ornithology Group of Sri Lanka (FOGSL) headed by Prof Sarath Kotagama . Bird ringing or bird banding is a technique used in the study of wild birds, by attaching a small, individually numbered, metal or plastic tag to their legs or wings, so that various aspects of the bird’s life can be studied by the ability to re-find the same individual later.

The World Migratory Bird Day is organized by the African-Eurasian Migratory Waterbird Agreement (AEWA) and the Convention on Migratory Species (CMS). Its theme focuses on how land use patterns affect bird migrations. Although these transformations are essential for the survival of the human race, they have quite literally, ruffled a few feathers

Black tailed Godwit, known to fly up to 4000 kilometres at a stretch

Marsh Sandpiper Flamingos at Bundala

There is no doubt that land use patterns continue to affect many a feathered friend. The theme of the World Migratory Bird Day (May 9 - 10) this year is how land use patterns such as urbanization, land reclamation and intensive agriculture, affect bird migrations. Although these transformations are essential for the survival of the human race, they have quite literally, ruffled a few feathers.

Every year migratory birds such as Geese, Thrush, Terns and Godwits fly thousands of miles to wait out the winter. Black tailed Godwit are known to fly up to 4000 kilometres at a stretch. “Migration is not a simple movement.” explained Colombo University Zoology Department Head Prof Sarath Kotagama.

He explained that bird migration is a by-directional movement, which takes them from their breeding to roosting grounds in the tropics and then back again. “Their paths are very clearly defined.” Prof Kotagama said that their ‘site tenacity’ is a factor that makes this phenomenon unique. Year after year they return to this same location. “It is a genetically built-in mechanism, rather than behavioural, as previously believed.”

Master navigators

Studies on general migration indicate that the birds could be using stars as celestial maps. “Some believe they use geomagnetic fields,” he explained. “Or they maybe going by geographic features,” such as the coastlines, rivers, vegetation patterns. Yet others believe that the birds make use of infrared light, using the position of the sun as a point of reference. As much as 47 percent avifauna in Sri Lanka, some 120 species, are migrants. Hundred percent of waders in Sri Lanka, except sub species of Kentish Plover and Little ringed Plover, that breed in Sri Lanka, make water edges their temporary home. Ninety five percent of ducks, 60 percent of birds of prey in Sri Lanka, such as Harriers and Buzzard, are also migrants. Sandpipers, Golden plover, Redshank and Curlews are among the common migrants.

“Terns and almost all gulls of the shore bird group are migrants. But the migrant forest bird group comprising Indian Pitta, Brown shrike and a number of Warblers, is comparatively small. Those who can be found in the hill country include Kashmir Flycatcher and Pied Thrush. Indian Blue Chat is one of a small group of migrant ground birds.

Major migrant destination

The reason that Sri Lanka is a major migrant destination is that there is no other land mass south of the island, making the island a much sought after feeding ground for spring breeding winter migrants, explained Prof Kotagama.

They come only for feeding and go back for breeding, which is why they are referred to as migrants. However according to anecdotal evidence a certain bird group has chosen to stay behind and breed. “There is a breeding population of Blue tailed bee-eaters around the Kumana Santuary and Udupotthana in Yala Block 2.”

But this does not disqualify Blue tailed bee-eaters as migrants; apparently it is only a small group.

The birds start migrating southward because of the food scarcity in August that precedes winter. By mid April they are gone. “The food availability does not change in the south.” Tropical countries are not subject to seasonal variations to have any significant effect on food availability.

So why go back? Prof Kotagama explained that they go back because their home breeding grounds are ideal for bringing up chicks, in the Spring. “The days are longer in the north.

This provides more feeding time for the chicks.” Moreover the predator pressure in the north is also low compared to the tropics.

Threats

Deforestation and mineral extraction continue to damage entire regions. It has removed, degraded and fragmented large areas of habitat in the Amazon in South America. Urbanization, most acute in the European region, not only deprives migratory birds of their habitat, but its by-products, such as noise and light pollution, disorient them, while urban wastewater and air pollution render these habitats virtually useless. Physical structures like skyscrapers kill millions of migrant birds every year.

Wetlands are feeding grounds where migrating birds feed and refuel for the return journey. Land reclamation promotes development in these areas. Intensive agriculture uses large amounts of pesticides, herbicides and fertilizers that can be harmful to these migrating birds.

According Prof Kotagama, Sri Lankas wetlands have not drastically reduced to pose a major threat. There was once a danger of losing brackish coastal habitats to aquaculture, but since then most of these have been restored. “Much of the northern coastal stretch, including the salterns in Elephants pass, Vankalai and Mannar has been virtually untouched due to the war.”

On the other hand, compared to wetland depletion, the damage to Sri Lankan forest cover has been much greater. “Forest cover continues to decline. However since 2000, the rate of deforestation has gone down.”

Where are the Flamingos

Bundala is a particular problem associated with the previously mentioned ‘site tenacity’. A question all conservationists ask is ‘where are the flamingos?’ “There used to be 1000 to 3000 flamingos at Bundala during the migratory season, now there are hardly any.” The reason is the conversion of the habitat from brackish to fresh water, which has made a huge impact on the ecosystem from 1994 to 2004. “This is due to the Lunugamwehera agricultural freshwater inflow” explained Prof Kotagama.

Protection for birds, both legal and social, have been high in Sri Lanka. As opposed to European countries, hunting is socially discouraged, where the necessary legal protection is provided by the Fauna and Flora Protection Ordinance. How Sri Lanka will manage the sites located in recently liberated areas remains to be seen. “The preliminary surveys conducted at the Vankalai area found that many of the birds were attracted to abandoned paddy fields.” Paddy cultivation has been a traditional form of agriculture for many years. Will these important sites be re-cultivated? In which case it would lose its significance as a major roosting site.