Visiting near water bodies (rivers or lakes), everyone must have seen medium-sized and nondescript at first glance long-winged birds. They are commonly called gulls for distant similarities. In reality, this is a river tern (Charadriiformes). You can notice them by a characteristic flight and a sharp, slightly creaking voice in case of alarm. This is a fairly common species of birds, often forming large colonies. Being a numerous species, however, they are defenseless against predators, and indeed, by humans.
Krachka river: description
The species is very common and is found everywhere south of the tundra zone. It is an elegant pigeon-sized bird. The body length is from 30 to 35 cm, but with a large wingspan - 70-80 cm. Weight varies from about 100 to 180 g. The plumage is characterized by an inconspicuous light gray hue or white. On the head of the "hat" glossy black. Only the red beak (with a black top) and paws give brightness. The river tern may have a very diverse voice, but a sharp one with a characteristic crack, creaky prevails, it sounds something like a kierr, sometimes a more quiet and calm ki-ki.
Appearance really strongly resemble a small gull. However, the tern has narrower and longer wings. The second difference is the tail, it has a deep neckline, like a swallow. And the third - a black "hat" on the head.
Adults undergo molting twice a year - pre-nuptial full and partial. As a rule, it takes place during the winter.
Habitats and distribution
The nesting area is wide enough. It extends throughout the Palearctic, except in the Far North, where this species is replaced by the Arctic tern. It also occurs on the North American continent. River tern nests almost throughout Europe, both in inland waters and on sea coasts. In the south, the habitat in the form of separate settlements reaches Senegal, Mauritania, Tunisia, and Israel. Irregular nesting is observed in Libya, Morocco, Syria and Cyprus. And isolated areas of the range are in Turkey, Afghanistan, Iran, Iraq and Pakistan. This is a migratory bird, and in winter it migrates to warm regions: New Guinea, Africa, the Philippines, the west of the South American continent.
Cases of the settlement of river terns in the tundra were noted, however, unlike its polar congener, there it chooses river valleys. She avoids the typical tundra landscape.
It lives mainly on pebble and sand spits, along the shores of lakes (in the lowlands), on flat sea coasts, in the valleys of large rivers. Moreover, for nesting, he chooses not only flat areas, but also mountainous areas at an altitude of up to 4800 m (in Tibet, Pamir). In general, according to the observations of ornithologists, the tern prefers still standing reservoirs and calm rivers with a slow course.
River tern: food
This is primarily a good hunter. The diet consists mainly of small fish and mollusks; it easily rushes into the water behind them, plunging to the very wings. Favorite habitats are sand spits and shallows along the banks of water bodies, especially large rivers. In shallow water, it is much easier for her to get prey, mainly fry. She peeps out her prey, hovering in one place in the air. In addition, dragonflies, flies, various beetles, locusts, etc. are eaten.
Feeding places are large reaches, shallow waters, and these birds can catch insects on the fly, similar to swallows. During the nesting period, they can fly for forage at distances that generally do not exceed 10 km, in rare cases, 20-26 km.
Forming large flocks and colonies, river terns can harm fisheries. However, this is rare and, as a rule, they hunt alone for species that do not have commercial significance.
Nesting
The ability to reproduce occurs at 3-4 years of age. Birds are monogamous and, in almost 80% of cases, retain a pair for at least two seasons. Tern males are characterized by a special mating behavior. It is expressed in an aggressive demonstration, the adoption of a bent posture, lowering the beak to an almost completely vertical position, the tail upturned.
The river tern equips its nests on the shallows (sandy or pebble), as a rule, as part of a large colony, and it even happens that together with other birds. This is primarily due to the need for collective protection from predators. Alone, the bird is not able to protect its nest and chicks. And in cooperation, they attack the "robber", beat him with his beak and stun them with their cries.
River terns choose places with a little vegetation. Tern nests are built right on the ground. It has the appearance of a small hole made in the ground. Litter in it, if it happens, is very scarce, made of dry grass and feathers. The diameter of the nest is 8-10 cm.
Breeding chicks
Breeding times vary quite a lot depending on several factors, including habitat. Birds arrive from the southern edges closer to mid-May; the first clutches can be found already in the first half of June.
The river tern in the masonry usually has three eggs, much less often four; they have a green-ocher or olive hue with specks of brown or almost black color. The eggs are small in size, from 3.8-5 cm in length and 2.9-3.2 cm in width.
The process of hatching the river tern (photo can be seen above) starts from the moment of laying the first egg, and this period lasts an average of about 20-22 days. It is carried out alternately. The female sits at night, the male most often replaces her only during the day. The chicks begin to hatch in early July, and by August they are able to fly (about 25 days after hatching).
Tern subspecies
In total, it is customary to distinguish four subspecies, the differences often relate to the color of plumage, beak, legs, body and wing sizes. We give their Latin names and a small description.
- Sterna hirundo hirundo. These are the lightest birds, they do not have a brown shade in plumage. The beak with a black top is red, as are the legs. Conventionally, they are called the nominal race.
- Sterna hirundo minussensis. The specimens are darker in color, the black area on the beak is more pronounced. The color of the legs varies from bright red to brown.
- Sterna hirundo longipennis. Even more river tern (see photo in the article). She has a wide black stripe on her beak. In some individuals, especially in populations in the East, it is completely dark. The color of the legs of the birds also changes markedly to brown or black.
- Sterna hirundo tibetana. It is the darkest in body color; on top they have a brown coating. But the legs and beak are red.
Natural enemies
River tern (photo) - a bird susceptible to attack by larger relatives. Colonies are damaged by corvidae (most often they are ordinary gray crows), large gulls (bluish and silver species). Mammals also do not bypass their nests. Ermines, weasels, foxes, raccoon dogs and even wild boars are a threat, and in warm areas masonry and small chicks can suffer from the steppe viper.
Environmental impact
In addition to predators and destroyers of tern nests, like all living organisms around, the environment has a great influence. Perhaps the most unfavorable, dangerous and more common factor is a sharp increase in water levels in places where terns settle. It can be caused by strong winds, prolonged rains or spring floods, etc. As a result, the entire colony or the main part of the clutches can die. In addition, prolonged rains during the breeding season affect the fecundity of birds.
Man is also relevant, and it should be considered in two aspects, as a predator and as an adverse environmental factor. The harm is done in various ways - from seemingly harmless noise in places where river tern lives (which worries birds), to collecting eggs and grazing in the colony.
Any animal or bird, plant is beautiful in its own way. In simplicity lies the grace of river terns. Having a fragile body structure, she is, nevertheless, a wonderful hunter. Her flight is akin to planning - easy and carefree.