Being near water bodies (rivers or lakes), everyone must have seen medium-sized and inconspicuous at first glance long-winged birds. In the people they are called seagulls for a distant resemblance. In fact, this is a river tern (order Charadriiformes). You can notice them by their characteristic flight and a sharp, slightly raspy 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, in fact, humans.
River tern: description
The species is very common and is found everywhere south of the tundra zone. It is a graceful bird the size of a dove. 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 characteristically inconspicuous light gray or white. On the head is a "hat" of glossy black color. Brightness gives only a red beak(with a black top) and paws. The common tern's voice can have a very diverse voice, but it is dominated by a sharp with a characteristic crackle, creaky, it sounds something like "kierr", sometimes a quieter and calmer "ki-ki-ki".
The appearance really strongly resembles a small seagull. 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 "cap" on the head.
Adults twice a year experience a molt - full prenuptial and partial. As a rule, it takes place in winter quarters.
Habitats and distribution
The nesting area is wide enough. It extends throughout the Palearctic, except for the regions of the Far North, where this species is replaced by the Arctic tern. It is also found on the North American continent. The common tern nests almost all over Europe, both in inland waters and on sea coasts. In the south, the habitat in the form of separate settlements reaches Senegal, Mauritania, Tunisia, Israel. Irregular nesting is observed in Libya, Morocco, Syria and Cyprus. And isolated parts of the range are located in Turkey, Afghanistan, Iran, Iraq and Pakistan. This is a migratory bird, and in winter it migrates to warmer regions: New Guinea, Africa, the Philippines, the west of the South American continent.
There have been cases of a settlement of the common tern in the tundra, however, unlike its polar relative, it chooses river valleys there. She avoids the typical tundra landscape.
Inhabits mainly onpebble and sand spits, along the shores of lakes (in the lowlands), on flat sea coasts, in the valleys of large rivers. Moreover, for nesting, it chooses not only flat areas, but also mountainous areas at an altitude of up to 4800 m (in Tibet, the Pamirs). In general, according to the observations of ornithologists, the tern still prefers stagnant water bodies and calm rivers with a slow flow.
River Tern Food
This is first and foremost a good hunter. The diet consists mainly of small fish and shellfish, it easily rushes into the water after them, plunging at the same time to the very wings. Favorite habitats are sandbars 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 looks out her prey, hovering in one place in the air. In addition, dragonflies, flies, various beetles, locusts, etc. are eaten.
Feeding places are large stretches, shallow waters, and these birds can catch insects on the fly, similarly to swallows. During the nesting period, they can fly for food over distances, mostly not exceeding 10 km, in rare cases 20-26 km.
By forming large flocks and colonies, common terns can wreak havoc on fisheries. However, this is rare and, as a rule, they hunt singly for species that have no commercial value.
Nesting
The ability to reproduce occurs at 3-4 years of age. Birds are monogamous and in almost 80% of cases keep a couple for at least two seasons. Male terns are characterized by a specialmarital behavior. It is expressed in an aggressive display, adopting a bent posture, lowering the beak to an almost completely vertical position, tail up.
The river tern builds its nests on the shallows (sand or pebble), as a rule, as part of a large colony, and sometimes even together with other birds. This is primarily due to the need for collective protection from predators. Alone, a bird is not able to protect its nest and chicks. And in cooperation, they attack the “robber”, beat him with their beak and stun him with their screams.
River terns prefer places with little vegetation. The tern's nest is built right on the ground. It looks like a small hole in the ground. The litter in it, if it happens, is very meager, made of dry grass and feathers. The diameter of the nest is 8-10 cm.
Hatchling
The timing of reproduction varies quite a lot depending on some 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.
River tern in clutch usually has three eggs, much less often four, they have a green-ocher or olive hue with brown or almost black speckles. The eggs are small in size, between 3.8-5 cm long and 2.9-3.2 cm wide.
The process of incubation of the common tern (photo can be seen above) starts from the momentlaying the first egg, and this period lasts an average of about 20-22 days. It is carried out alternately. The female sits at night, while the male most often replaces her only during the day. Chicks start hatching in early July, and by August they are able to fly (about 25 days after hatching).
Subspecies of the common tern
In total, it is customary to distinguish four subspecies, the differences often relate to the color of plumage, beak, legs, body size and wings. Here are their Latin names and a short description.
- Sterna hirundo hirundo. These are the lightest birds, they do not have a brown tint in plumage. The beak with a black top is red, as are the legs. Conventionally, they are called the nominal race.
- Sterna hirundo minussensis. Individuals 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 birds also changes noticeably to brown or black.
- Sterna hirundo tibetana. This is the darkest in body color, on top they have a brown coating. But the legs and beak are red.
Natural enemies
The river tern (photo) is a bird subject to attack by larger relatives. Colonies are damaged by corvids (most often they are ordinary gray crows), large gulls (gray and silver species). Mammals also do not bypass their nests. Stoats, weasels, foxes, raccoon dogs and even wild boars pose a threat, and in warm areas, masonry and small chicks can suffer from the steppe viper.
Environmental impact
In addition to predators and nest destroyers, terns, like all living organisms around, are greatly influenced by the environment. Perhaps the most unfavorable, dangerous and most common factor is a sharp increase in the water level in the places of tern settlements. 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 may die. In addition, prolonged rains during the breeding season affect the fertility of birds.
A person is also related, and it should be considered in two aspects, as a predator and as an unfavorable environmental factor. Harm is caused in a variety of ways - from seemingly harmless noise in places where the common tern lives (which disturbs the birds), to the collection of eggs and grazing in the colony.
Any animal or bird, plant is beautiful in its own way. In simplicity lies the elegance of the river tern. With a fragile body structure, she is nevertheless an excellent hunter. Her flight is akin to planning - easy and carefree.
