Colours of Wildlife: Sooty Terns

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Sooty Terns

Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"

Sooty Tern by Willem

Here you see something very, very unusual. These are Sooty Terns, Sterna fuscata. They're actually one of the most abundant species of seabirds. So, what's so unusual about them? It is that these were found inland – they're now residing in the Wolkberg Animal Clinic in Polokwane, having turned up in the surrounding regions, hundreds of miles from the sea. How did they get here?

You'll have the answer from weather reports. South Africa has been impacted by Cyclone Eloise over the past few days (late January 2021). We've had torrential rains in the northeastern parts of the country. But actually the biggest impact of the cyclone was over the ocean itself. Now these terns are, as I've said, properly seabirds. Not only that, they're some of the most aerial of all bird species. They breed on islands in the ocean, in tropical and subtropical waters all over the globe.

The thing is, they only come on land to breed. They nest on the ground, bare or somewhat sheltered by surrounding vegetation. Their nests are only shallow depressions at best. The female lays a single eggs most of the time, rarely 2. The parents bring their chick fish and squid, and it grows rapidly. In about two months, it fledges. And then it leaves the nesting island together with its parents. It doesn't return to land until it is itself ready to breed. They typically start breeding at the age of six – so for all those years, they remain at sea – more properly, over the sea.

Sooty Tern by Willem

Yes. They spend years on the wing without interruption. They're not equipped to rest on the water or to swim; indeed, their feathers easily become waterlogged. They feed just by dipping their beaks into the water, or with shallow plunge-dives at most, emerging immediately and swallowing their catch on the wing. They also snatch flying fish in mid-'flight'! They feed at night, on fish, squid and some crustaceans that only come towards the surface after dark. By day, they rest. While remaining in the air. They even sleep on the wing! This amazing ability they share with the other (but not at all closely related) extreme aerial specialists, the swifts. Their sleek design, with light bodies on extremely long wings, is so aerodynamic that they can remain aloft with minimal effort.

Sooty terns hunt and feed over vast stretches of the ocean. The problem is that in the very same tropical oceans they inhabit, there are regularly some extreme atmospheric disturbances. Such as cyclones. Cyclone Eloise was a particularly powerful cyclone. These conditions of strong winds and torrential rains are very bad for the terns. They get blown about the winds, and/or try to flee ahead of the storms, and for many of the sooty terns, this means getting away from the sea and into the continental interior. And this is precisely what happened. Very large numbers of terns must have been displaced from their usual haunts by cyclone Eloise. They arrive here exhausted and often dehydrated, as after many days of flying and being unable to feed. They are forced down to land in this exhausted state, in what is to them a very hostile environment and with no sources of food.

This must have happened to thousands of birds. We only hear from the ones noticed by people. There must be thousands that landed in various parts of Africa without anyone having seen them. They would then be in great trouble. Mostly they would be too exhausted to fly back to the ocean. Many would then surely die. Those that are found by people, can be helped. But people who see them need to know what they are and what sort of help they need. Here in Polokwane, we take them to a local vet, who feeds them and lets them rest, and later we take them back to the seaside. From there they should be able to fly back to their feeding waters. Terns certainly have a great sense of direction, and can travel thousands of miles over the oceans with little effort.

Sooty Tern by Willem

Apart from cyclones, sooty terns face many other challenges and threats. The fishes of the oceans also go through cycles of abundance and scarcity. During good years, many fish are available and the terns breed and raise their chicks successfully, but in poor years there can be massive, widespread breeding failures and chick starvations. They're probably to some degree impacted by human fishing, though they tend to focus on fish too small to be of much interest to humans. They do suffer from oil and other pollution of the oceans. On some colonies, people collect some of their eggs. The worst impact is from rats and cats introduced to some of the islands where they breed. Under natural conditions, they nest on the ground, making their eggs and chicks vulnerable to all land predators. Consequently, they nest only on islands that are predator-free. But several such islands that used to be safe havens, now have rats and/or cats that have been recently introduced to them by people, and these have caused the numbers of terns to plummet on those islands. But fortunately there are still many predator-free islands for them to breed on, and they are still abundant overall. There might be more than fifty million adult birds of the species all over the world. Sooty terns, like many seabirds, are quite long-lived, and an adult that survives chickhood might live for over thirty years.

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