Society

Terns in Chennai

A flock of White-winged terns over Pallikaranai Marsh. Photo: Sundaravel Palanivelu  

Terns are not difficult to track. With a roosting pattern that ticks to the tidal clock, they may however come across as putting in a slightly irregular appearance.

So, here is a tern-watching tip: Follow the low tide, find the tern. It is a tip Chennai nature lovers would do well to remember: Around a dozen tern species hit its coast during the migratory season.

Ornithologist V. Santharam unravels this pattern.

“People tend to see these birds (terns) more when they go on pelagic trips, or in coastal areas where these birds come to roost. During low tide, terns roost on the sand banks and when the water level rises, they fly away. They may go out in the night, depending on the tidal movement. They are not strictly diurnal, and their movements are based on the ebb and flow of tides.”

Common Tern. Photo: Sundaravel Palanivelu

Common Tern. Photo: Sundaravel Palanivelu   | Photo Credit: Sundaravel Palanivelu

While conceding that waders also sync their roosting behaviour with the tidal movement, Santharam spells out the difference: “Usually, terns roost on the mudflats during low tide, and waders during high tide. Waders usually need shallow open mudflats to feed on, and so with high tide, the entire area being covered with water and only small parts staying uncovered, these birds are left with little opportunity to feed. So, waders would rather go and ‘rest the high tide’ out. In contrast, terns roost when there is low tide, as it gives them enough place to park themselves on; and they go into the sea during high tide. As with many other things about terns, even this one has to be studied.”

The high flier

Among the striking physical features of terns is how they look aerodynamically-enhanced. Comparisons are indeed odious. But they are also the best bet in bringing uniqueness into the light of unmistakable knowledge.

Standing, a gull may appear heavier; and a tern, better stream-lined. The latter is something of a Polaris Slingshot. A three-wheeled motorcycle, the Slingshot tapers off finely, as does a tern. Parked, it looks ready for take-off.

Santharam underlines how terns are built for long-distance flying. One of the easily-recalled faces of long-distance migration is that of a tern. The Arctic Tern does an impossible Arctic-to-Antarctic annual “flyathon”.

The Caspian Tern seen around Chennai’s coastal sections during the migratory season is also an icon of long-distance migratory flying.

Once here, the migratory Caspian Tern knows how to make itself at home, even found a bit inland in coastal marshlands.

Birdwatchers in these parts would not be surprised to come upon congregations of Caspian Terns in the Perumbakkam wetland.

“Perumbakkam can be considered part of the coastal marshlands. ‘Coastal’ would include waterbodies that are within three to four kilometres from the seashore. But, during the migratory season, finding them in waterbodies far from the coast may be difficult,” points out Santharam.

The appointed time

The White-winged Tern is among the relatively rarer migratory terns to sight around the Chennai coast.

“The White-winged tern is a passage migrant. It comes around this time — March and April, on reverse migration, when one can find it along the Chennai coast, on coastal sections like Sholinganallur. It comes only for a short period. In the non-breeding season, it can be confused with the Whiskered Tern. During the breeding season, its plumage with its white wing offset by the black in the head and neck and down to the belly, makes it strikingly distinct. The next two weeks is the time to look for them,” says Santharam, adding that during this narrow window, large numbers of White-winged Terns can be sighted. So, a White-winged Tern sighting is bound to happen in Chennai if you know the when of it.

To illustrate, birder Sundaravel Palanivelu is accustomed to meeting up with hordes of White-winged Terns in March-April around Sholinganallur-Perumbakkam area.

On the morning of March 20, Sundaravelu Palanivelu witnessed “a flock of around 200 White-winged Terns, flying over the Perumbakkam Wetland.” A couple of weeks earlier, he had witnesed and shot a video of a murmuration of White-winged Terns over the Pallikaranai Marsh.

Possible discoveries

The terns seen around Chennai are visiting migrants. Santharam however underlines that some species could be breeding around Sri Lanka and in places on the South Indian Coast.

“The Greater Crested Tern (a winter migrant in Chennai) breeds around Sri Lanka and probably even around Rameswaram. They are also known to be breeding off the West Coast. I have seen Greater Crested Terns in Lakshwadeep, but not breeding,” he says. “During the migratory season, Point Calimere would be the place to spot both Greater and Lesser Crested Terns, as also Caspian Terns.” Amidst abounding knowledge about bird distribution and behaviour due to technology and citizens’ science, birds still manage to fly under the radar, keeping parts of their lives couched in a mystery.

Greater Crested Tern. Photo: Sundaravel Palanivelu

Greater Crested Tern. Photo: Sundaravel Palanivelu   | Photo Credit: Sundaravel Palanivelu

“Sometimes, I have seen Caspian Terns around the Chennai Coast after April and May and they probably breed off the Sri Lankan coast.” And on the Common Tern, Santharam makes this observation: “The Common Tern is known to breed on the coast of Sri Lanka, but in Chennai it is a winter migrant. It is possible that it is breeding in undisturbed places along South Tamil Nadu, probably around Mandapam.”

On how birds seldom cease to spring a surprise, he points out that Common Tern breeding has been reported from Ladakh.

More studies required

Santharam highlights the fact that terns could be better studied, and existing studies, especially of wintering terns, are thin on the ground. He draws attention to neighbouring Sri Lanka: Exemplary efforts over the last decade spotlighting terns in Sri Lanka have shown these birds to be breeding in greater numbers than previously believed. “Around a dozen species of terns come to Chennai during the migratory season. Regular monitoring can throw up interesting discoveries about their habits and habitat requirements.”

( ‘Migrant Watch’ is a weekly column about birds seen in Chennai during the migratory season)

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Printable version | May 9, 2021 11:27:39 AM | https://www.thehindu.com/society/terns-in-chennai/article34116092.ece

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