Pelicans, mangroves, and salt marshes

April 08, 2023 08:30 pm | Updated 08:30 pm IST

One of six: The Nelapattu Bird Sanctuary in Andhra Pradesh is one of the breeding sites for spot-billed pelicans.

One of six: The Nelapattu Bird Sanctuary in Andhra Pradesh is one of the breeding sites for spot-billed pelicans. | Photo Credit: File Photo

The island of Sriharikota serves as a barrier that shields a brackish water lagoon that we call the Pulicat lake. Being mostly off-limits to tourists because it is an ISRO launch site, this area is teeming with 76 species of water birds. The lake itself has an average depth of only one metre, although it is nearly 60 km long. 

The tidal flats, and both fresh and brackish water wetlands found here are ideal for the spot-billed pelican.

Although classified as ‘Near-Threatened’ in the IUCN red list, this bird looms large in our minds when we think of water birds. 

Blue spots

The spot-billed pelican’s comical walk points to weak leg muscles, which also means that the bird is not a great swimmer, and catches fish near the surface of the water. The common name comes from blue spots on the sides of the large bills. A social bird, this species sometimes goes fishing in groups, forming a semi-circle that pushes the fish towards shallow water. It also forms a foraging partnership with the little cormorant.

Cormorants are divers, and their dives cause the fish present in deeper regions to scatter towards the surface, where the pelican awaits them.

Adult spot-billed pelicans weigh 4.5-5 kg. The pouch, which is called the gular, is for catching fish. In the breeding season, the adult may bring home 2 kg of fish in one catch. Spot-billed pelicans form stable colonies along with other water birds. Nests are built on trees, and two-three eggs are laid. When they are about a month old, the chicks destroy the nests.

Breeding colonies occur very close to, or even within villages, and the birds do not seem perturbed by human activity, and the villagers welcome and protect the pelicans and the nests. Villagers use the droppings of the spot-billed pelican as a fertilizer. After the breeding season, pelican populations scatter over a very large area as they forage for food.

Breeding sites

A detailed survey of spot-billed pelican populations by Kannan and Manakadan (Forktail, Vol 21, 2005) placed a crude estimate of their number in India at 6,000-7,000. The survey identified breeding sites for these birds in South India at Karaivetti-Vettangudi near Thanjavur and Koonthankulam near Tirunelveli in Tamil Nadu, Kokkarebellur (Mandya District) and Karanji Lake (Mysuru city) in Karnataka, and Uppalapadu near Guntur and Nelapattu near the Pulicat lake in Andhra Pradesh.

Andhra Pradesh has recently lost a large breeding colony of the bird at the Kolleru lake, where aquaculture has contributed to a total degradation of the ecosystem.

Paleobotanists have shown that the Pulicat lake, now a salty marsh, was a thick mangrove forest in the 16th century. Wetland ecosystems lock up carbon dioxide from the atmosphere, as ‘Blue Carbon’. As carbon sinks, mangroves can store 1,000 tonne of carbon per hectare.

Ramsar sites

Wetlands of global importance are called Ramsar sites, after the city in Iran where the Treaty on Wetlands was signed.

India has 75 Ramsar sites, of which 14 are in Tamil Nadu, including three added last year: the Karikili bird sanctuary, the Pallikaranai Marsh Reserve Forest and the Pichavaram mangrove. The spot-billed pelican is seen in all these places.

(The article was written in collaboration with Sushil Chandani, who works in molecular modelling.

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