LITTLE TERN IV

Motif: Little Tern (Sterna albifrons) The Croatian Post has issued four commemorative postage stamps with the motif of the Little Tern in cooperation with the Worldwide Fund for Nature – WWF, and the sign of the panda - the logotype WWF, is printed on the stamps with the permission of the registered owner of the protected sign. Rivers with their shingle and sandy shoals and islands, shallows and limans, rapids and silence, whirlpools and beams, backwaters and pools, land-slide sloped river banks and many other shapes that are produced by rivers, all these belong to the most beautiful, most attractive and most endangered landscape riches in Croatia and Europe. In Croatia, the little terns settle just in such habitats and in many ways share their destiny: they belong to the most beautiful, most attractive and most endangered bird species. Little terns are the smallest, but at the same time the most elegant and adroit of our terns. Their body is slender (22 to 24cm in length from the tip of the bill to the tip of the tail), so they are very light – weighing only 40 to 60 grams. Their wings are very long (the wing-span is from 50 to 55cm). This is the reason their flight is very easy, dexterous and harmonious. This way of flying is very important for the little terns because they feed on small fish, crustaceans and insects, all of which demands a continuous flight above the river, particularly above the river shallows and backwaters. While catching them they fly low above the river, between 2 to 3m, up to 10 to 20m high above the water surface. When they spot a fish or crab they plunge through the air and dive into the water to catch their prey. If they cannot see their prey properly, they vibrate above it before plunge-diving for it (vibrating is a special type of flying when birds moving their wings “stand” or keep still in one place) in order to see better. Doing this they make sure that the sunlight should be behind their backs in order to see their prey better and for their prey to fail seeing them. The success in their hunt, depending on the visibility (visibility is decreased by the muddiness of the water, the wavy surface, etc.) varies from 60 to 20 percent. The small fish they feed on are usually 4 to 6cm in length, the biggest are not longer than 10cm. Except for hunting in the water, little terns hunt for insects while they are flying, usually low above the water surface. Little terns nest in colonies on barren or slightly overgrown, usually gravel islands, mostly in co-habitation with the larger and more numerous red-billed common terns. They make up pairs at the time of the spring migrations or upon coming to their nesting places in the course of May, and the pair usually remains together for a number of nesting seasons. The nest is a shallow cavity, usually covered with some grassy material. They usually lay two to three eggs, and both partners sit on the eggs, though the female does it for longer periods. The chicks hatch after 21 day, and both parents alternate in feeding them and caring for them. While the chicks are small, the female remains in the nest all day and keeps them warm. During that time the male hunts on its own and feeds the chicks and the female. When the young little terns are 5 or 6 days old or older, both parents feed them and the chicks are temporarily left on their own. The young start flying in about twenty days’ time, and the parents continue feeding them for a bit longer, until they become independent. Many birds also remain in family flights in the course of the autumn migrations (the family flight consists of parents and their already independent chicks). Approximately two weeks after their first flying attempt, little terns abandon their nest and disperse in the wider surroundings. They start the autumn migration at the end of August and in September. The wintering habitat of the little tern spreads from the Atlantic coast of western Africa all to its extreme south and further on along the coast of the Indian Ocean to the north of Kenya, including the islands on the western part of the Indian Ocean. This makes the little terns real globe-trotters who fly during their migrations over distances of thousands of kilometres along the Mediterranean coastal line, across the Atlantic all to the Indian Ocean. They repeat this huge travelling distance twice a year, in autumn and in spring. Such a demanding migratory system together with the insecure, changeable habitat like the river, asks for lots of skill and experience to secure survival. This makes the little terns, compared to other small birds, long-lived. Those that survive the first few years gain sufficient experience and skill to be able to reach the age of 30 or even more years of life. In the continental part of Croatia little terns nest only in the upper course of the Drava river (two small colonies with a total of 5 or 6 pairs) and on the Sava river, downstream from Zagreb (one colony with some 20 pairs). This is why we consider the species highly endangered and there is an immediate threat of their extinction in the continental part of Croatia. They are mostly threatened by the permanent river regulation and canalization of the river courses or the flooding of rivers by artificial lakes. Along with the population of the little terns nesting by the rivers in northern Croatia, there is a smaller population that nests in the area of the northern part of the islands of the Zadar area up to the island Pag. On these small, bare islands there are 4 to 6 colonies (depending on the year) with a total of 30 to 40 pairs. These birds hunt for food in the shallows and bays in the same way as those by the rivers. Unfortunately, this population, too, is threatened, mostly on account of the ever growing pressure of tourism, recreational activities and fishing trade. Dragan Radović