Sooty Shearwater: The Champion Migrants of the Avian World

Sooty Shearwater
Bird migration is one of the nature’s most extraordinary wonders. Every year our entire globe is criss-crossed by millions of birds belonging to different species which fly thousands of pain staking miles along the length and breadth of planet earth finally augmenting in their dream destinations. And subsequently their return journey is performed a few months later to their native places after spending their holidays.
Sooty Shearwater: 
The Champion Migrants of the Avian World

-Rahul Rohitashwa 

Bird migration is no doubt a fascinating phenomenon of nature and therefore has consequently mesmerized everyone ranging from common people to the scientists since time immemorial. Actually bird migration is the regular seasonal journey undertaken by many species of birds. Bird’s movements include those made in response to changes in food availability, habitat or weather etc. Flocks of migratory birds are like a parade in the sky. 

Bird migration is one of the nature’s most extraordinary wonders. Every year our entire globe is criss-crossed by millions of birds belonging to different species which fly thousands of pain staking miles along the length and breadth of planet earth finally augmenting in their dream destinations. And subsequently their return journey is performed a few months later to their native places after spending their holidays. The works on bird migration have always been a great mystery to man and still today many questions as to how birds find their way and what makes them set out on their journey remains enigmatic.

In this perspective it is not an exaggeration to state that seabirds are marvelously adapted for covering enormous distances over trackless oceans and therefore they are considered as champions among the migrants. As for instance with an eye to the bird migration since a long time it is deeply penetrated both in the minds of common people as well as of scientists that the Arctic Tern’s migratory pattern is an unknowable biological mystery and wonder of the natural world. It is so because the breeding range of this bird includes the northernmost coast of Europe, Asia and North America. 
They spend their winters in the extreme Southern Pacific and Atlantic coastal areas chiefly along the Antarctic Rock ice 17,600 km i.e. almost 11,000 miles from their breeding range. Thus, they travel farther than any other bird species known till date. During its migration activities the Arctic Tern enjoys more daylight by experiencing both the polar summers each year. This bird breeds from the Arctic coasts to Alaska, Greenland, Canada, Europe and Siberia and winters in the southern continental latitudes eventually reaching the Antarctic ice edge. 

Arctic Terns have been known to nest within 220 km of the North Pole and some of them actually circumnavigate the globe covering approximately 40,200 km between successive breeding seasons. But in the light of recent studies scientists have discovered that the Sooty Shearwater (Puffinus griseus) a small nomadic bird having, sooty brown colour, dark billed, dark legs, slim pointed wings and having a wing span of almost 100 cm which is confined mainly to offshore and pelagic waters of New Zealand and Chile has been scientifically proved to have the longest migrating pattern. They migrate nearly 40,000 miles (64,000 kilometres) a year, flying from New Zealand to the North Pacific Ocean every summer in search of food and fodder according to the new study.

The Sooty Shearwater (Puffinus griseus) is a medium-large bird falling in the seabird family Procellariidae. In New Zealand it is also known by its Maori name titi and also as "mutton-bird" like its relatives the Wedge-tailed Shearwater (P. pacificus) and the Australian Short-tailed Shearwater (P. tenuirostris). Sooty Shearwater appears to be closely related to the Great and Short-tailed Shearwaters which are blunt-tailed, black-billed species with long, dark, hooked top mandible, but its precise relationships with those shearwaters are obscure. Genders are similar with overall dark, dull brown plumage that appears blackish on the tail and wingtips.

Sooty Shearwater is almost 51 cm in length with a 110 cm wingspan. It has the typically "shearing" flight, dipping from side to side on stiff wings with the wingtips almost touching the water. Its flight is powerful and direct, with wings held stiff and straight, giving the impression of a very small albatross. The sooty shearwater is also identifiable by its dark plumage which is responsible for its name.. These birds are generally docile in nature, but during the mating season they use a rhythmic, low pitched moaning or braying call. While arguing over food, they use series of noisy squeaks, and this can be particularly audible near large feeding flocks. Sooty shearwaters are very social birds that congregate in flocks of more than one million individuals. In-flight, they have a pattern of several fast flaps followed by a stiff glide just a few feet above the surface of the water.

Sooty Shearwaters breed on small islands in the south Pacific and south Atlantic Oceans, mainly around New Zealand and also in the Auckland Islands , Norfolk Island and also in the Falkland Islands near Argentina. They start breeding in October, and incubate their young for about 54 days. Once the chick hatches, the parents raise their chicks for 86 to 109 days. At the end of the nesting season in the months of March to May, they reach sub-Arctic waters in the months of June to July where they cross from west to east and then return south down the eastern side of the oceans in the months of September to October, reaching to the breeding colonies in November. Amazingly they do not migrate as a flock but rather as single individuals.
Sooty Shearwater feeds mainly on surface zooplanktons. Usually, they chatter along the surface water of the sea scanning for their prey. But at irregular intervals, they can also dive deep in the sea for food. This bird is a very robust diver and can swim easily underwater, reaching depths up to 30 feet in search of food such as fishes, squid, shrimp-like krills and other crustaceans. Usually, like other diving birds nature has also provided sooty shearwater with a thick lining of down feathers in the ventral part of their belly which is water-resistant in nature and thus helps this bird to find food in the chilling water of the oceans.

Sooty shearwaters are one of the most widespread pelagic birds and they can be found throughout the world. While they prefer to stay far out at sea, they are occasionally found close to land in times of high onshore winds or near deep coastal bays. During the summer months, they are most common in northern waters of both the Atlantic and Pacific oceans, and they continue their cyclic migration to all the world's oceans in the winter. 

They are infrequent however reports about their scanty presence have been reported by some ornithologists in the Indian Ocean and near the Pacific coast of China. Scientists have long been known that sooty shearwaters breed in New Zealand and Chile and migrate to feeding grounds in the Northern hemisphere. But the details of their remarkable trans-equatorial migrations are now emerging from a recent study using electronic tracking tags.

Upon vigorously contemplating the data gained from electronic tags scientists jumped to the conclusion that these birds leave New Zealand in the Southern Hemisphere in the winter and summer in the Northern Hemisphere taking advantage of the prevailing winds along different portions of their migration route. In the course of their migration these birds flew fastest over the equatorial region almost about 620 miles i.e. 1000 km in a single day. These small sea birds crossed the equator twice a year in pursuit of an endless summer feeding near the period of peak productivity. 

The diving patterns recorded by the electronic tags revealed that these birds stopped little to feed as they pass through the equatorial regions of their journey. Investigators were also astonished to discover that once breeding pairs had reared their young ones they had also taken their separate journeys. The data also proved that due to high productivity these birds dived to a depth of almost 30 feet under water so as to catch fish, squid, krill and other aquatic animals to fill its belly near Antarctica during the summer and then zipped to North Pacific to accomplish their journey.
The targeted study also showed that contrary to the previous assumptions sooty shearwaters do not make a big Pan-Pacific sweep to cover all of their feeding areas in the Northern Hemisphere instead individual birds went to just one of the major hot spots and stayed there until time to return Southern Hemisphere to breed. The timing and route of the northward migration was somewhat variable with birds crossing the equator at various locations but the return trip was remarkable synchronous.

sooty shearwater birds
Thus it can be said that with the help of sophisticated technology researchers along the length and breadth of the earth are unearthing more and more hidden facts pertaining to bird migrations in the best possible manners which were masked since a considerable long time. 

These studies not only usher people to look deeply into the marvellous, mystique and daring lives of birds but also persuade them to protect and conserve them. As for instance the Sooty Shearwater are considered as one of the most abundant bird species in the world with a global population of about 20 million birds. But sadly to state that according to the recent report of IUCN (International Union of Nature and Natural Resources) they have been classified as near threatened species because their numbers have been decreasing in the recent years. Scientists have reported their recent population decline at breeding colonies in New Zealand and in the eastern North Pacific. 

The main reason attributed to this assertion is the global climate change which is affecting ocean productivity at an alarming rate. The increase in oceanic temperature and oceanic acidifications are perhaps causing limited regional biological productivity of zoo planktons and other one-celled organisms which are the staple diet of these birds. Without adequate food to consume the birds feel incapable of restoring their vigour and strength to fly back successfully.

The hazards these birds face due to human interferences are another factor which tends to jeopardize their population while they are in the process of migration. Human activities have threatened many migratory bird species and in this respect and they are also not an exception. The distances involved in their migration mean that they often cross the political boundaries of the countries. Hunting along their migratory route also takes a heavy toll. Structures such as power lines, wind farms and offshore oil-rigs have also been known to affect these migratory birds. Habitat destruction by land-use changes is the other biggest threat they encounter during their journey.

Eventually environmentalist around the nook and corner of the world unanimously agree to create the suitable environment for their proper protection and propagation otherwise due to our small mistakes these birds may vanish from the face of the earth forever. So the time recalls admiring the spirit of these wonderful birds so that the future generations also experience it without any interruptions.

Rahul Rohitashwa:   Free lance science writer, Environment and Wild Life Naturalist, Keen Bird Watcher & Involved in various Nature Conservation Campaign and as well as in Educational Activities.
Winner of Prestigious “Earth Eco-Warrior Award- 2008” by the Honorable Vice President of India in the field of Nature and Eco-Conservation activities in Bihar Twice Winner of “Prithvi Mitr (Friends of the Earth)” Award & “Yuva Rashtriya Pratibha Samman” by Earth Matters Foundation and Govt. of Bihar respectively.
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