Serving as the northerly stretched arm, the Bay of Bengal is a wide-mouthed opening to the Indian Ocean. The Bay holds an area of more than 2 million square kilometres, widens around 1,600 kilometres on average, and stretches up to 2,600 metres down into the sea with a dynamic bottom topography. She is the largest bay of the world.
The Bay of Bengal forms a distinct tropical marine biome, empowered by the tributaries of the largest delta of the planet. Being one of the world's 64th largest seaborne ecosystems, the Bay rims our coast with pride.
Because of the rich and vibrant benthic and pelagic fauna, the Bay offers suitable habitats for a myriad of bird species. There is a very special group of avian community that are dependent on the Bay's resources. They spend almost their entire life on the ocean, winged, wandering from place to place. These evolutionary awe-inspiring groups of seabirds are called pelagic birds.
Bangladesh, holding the lion's share of the Bay of Bengal, offers home to about a dozen different bird species adept in sea-faring lifestyles. There is not much that is known about them; pelagic birds are very rarely seen. Thanks to natural forces - storms, swells, and cyclones, they pop up from the least-expected places at times. In regular intervals, newer seabird names are being added to the country's checklist. This is an attempt to bring all the pelagic birds of Bangladesh under a single anecdote.
Defining a pelagic seabird
Pelagic birds have exceptionally long and thin wings that allow them to fly effortlessly for long periods without rest. Albatross, undoubtedly, are the ambassador of this group of seabirds. In fact, the wandering albatross has the longest wingspan among all the birds in the world and the gray-headed albatross holds the record for the fastest level flight compared to any bird.
However, there are dozens of pelagic bird species with a great range of sizes and geographic distributions. While the exact birds that are considered truly pelagic can vary depending on the characteristics assigned to seabirds. The most familiar types of pelagic birds include albatrosses, frigatebirds, fulmars, petrels, shearwaters, and tropicbirds.
Some birds are so heavily associated with coasts that they are called near-pelagic birds, even though they are not seabirds in the formal sense. These almost-seabirds include cormorants, gulls, pelicans, penguins, razorbills, skimmers, terns, and eiders. And, you cannot even discard penguins of the South Pole, and razorbills and auks of the North Pole, although they are not flighted species at all or only with weak wings. These birds, too, are completely sea-dependent.
Construing a formal definition of pelagic or seafaring birds is not easy. Biology of Marine Birds says, "The one common characteristic that all seabirds share is that they feed in saltwater; but, as seems to be true with any statement in biology, some do not."
However, pelagic birds bear some certain traits. Their wings are aerodynamic and super-strong. While they may land on the water's surface to rest occasionally, or will float briefly after hunting and feeding, they can spend most of their lives in the air. They only return to land to nest. Many pelagic birds have special salt glands. This allows them to drink seawater and discard extra salt accidentally ingested with their oceanic prey. The excretions from these glands are almost pure sodium chloride. To do this efficiently, some have even developed tubiform nostrils, also called tubenoses.
These are master divers. Boobies catch fish by diving from a height into the sea and continuing an underwater pursuit, a technique called plunged diving. They have air sacs on their face to brace and cushion the impact from heightened diving.
Bangladesh has seen two boobies: masked booby was noted in 2017 from an expedition to the Swatch of No Ground (SONG) led by Isabella Foundation. Red-footed booby was seen in 2020 in Cox's Bazar. The sub-adult specimen was displaced by the cyclone Amphan.
Both are highly interesting observations as boobies tend to live far in the southern part of the Indian Ocean.
Storm-petrels and shearwaters
These two tubenose groups share the same family. Storm-petrels are small birds, the smallest of all pelagic birds. Shearwaters are moderate in dimensions. Except for the breeding season, these groups always stay on the ocean. Both occur globally. Storm-petrels get their name as they are deemed as divine warning of storms. Shearwaters fly with stiff wings very close to the water and seemingly cut through the wave tips.
Short-tailed shearwater is often found in our Bay and is being observed since 2008. The cyclone Amphan brought two more species: Wedge-tailed shearwater and Wilson's shearwater. Both were swept by storm into the heartland of the country.
The former was seen in Dhaka by Seth Miller, the other in Rajshahi by Mainul Ahsan Shamim.
Skuas and frigatebirds
Some pelagic seabirds have one astounding way of acquiring food; a technique called kleptoparasitism. This behaviour is seen among larger and more robustly-built groups, involving an act of robbing smaller species off their prey. Skuas and frigatebirds are highly acrobatic, strong flyers, and predatory birds. Both are exceptionally infamous for this habit, often comprising 95percent of their feeding in the wintering periods. Frigatebirds are also reputed for their vibrant inflatable throat-pouch in males.
Here in Bangladesh, we have three relatively smaller skuas, also called jaegers. Pomarine jaeger has been seen in regular intervals - first in 2006, then 2008, and 2013 - according to a study published in "Forktail".
The Arctic skua, also known as parasitic jaeger, was first noted during the SONG expedition by the Bangladesh Bird Club. Shamim, an avid bird-watcher of Rajshahi Bird Club, claimed the third one – Long-tailed jaeger, blown away by the Amphan into the Ganges or Rajshahi.
The only frigatebird of Bangladesh is the lesser frigatebird – seen by Israt Jahan, an ornithologist, and a team of Bangladesh Bird Club in 2016. It was also believed to be vagrant, dispelled by stormy condition.
Terns form a board group of birds that have adapted to life in waters. In terms of habit and habitats, there are coastal terns (common tern, gull-billed tern), riverine terns (riverine tern, black-bellied tern, marsh terns, etc.), and terns that are largely pelagic. Of the pelagic groups, perhaps, the Arctic tern is the first name that hovers over thoughts. This species literally lives from pole to pole, making rounds each year in their lifecycle.
Bangladesh has recently got two pelagic species: sooty tern and bridled tern. Again, credit goes to the cyclone Amphan and efforts of the Rajshahi Bird Club members.
There is a smaller group of terns, called noddies, that used to live in Sri Lanka and the Andaman. They pose high chances to be seen in Bangladesh waters someday.
As the name suggests, this group loves the tropical oceans. Tropicbirds are likely to be the most beautiful among winged seafarers. These birds are sleek and develop long tail-streamers in adulthood. They are used to living in solitary, pairs or smaller flocks and avoid mixed-species hunting frenzies – all uncommon in any other pelagic birds. Pair fidelity is high in tropicbirds, they often put up magnificent pair-forming aerobatic maneuvers.
Only red-billed tropicbirds fly over maritime Bangladesh. They were discovered during the 2013 expedition of the Bangladesh Bird Club.
Know before they are gone
Bangladesh has now entered into the era of the blue economy. Dots of project sites are speckling over the Bay, seemingly resembling a string. To thrive on what the concept of blue economy offers – the best utilizations of maritime resources for boosting economic growth, improved livelihood, better job opportunities, and sustainable ocean ecosystem health – we must not convert the string into a noose.
We need to do more and more systematic and scientific explorations in our maritime waters. The better we can know the lives on the bay, the safer refuges we can build – for the fish, for the birds, and ultimately, for us.