Common tern Sterna hirundo
In Poland, the species is subject to strict protection, requiring active protection; In Europe, it is considered an unthreatened species whose protective status is probably appropriate.
What does it look like?
Common tern is a small bird, similar to a gull. The dimensions of her body are from 30 to 39 cm. The coloration of the river tern is white-gray, with a black top of the head. The size and color of both sexes are the same. The final plumage, differing depending on the season (the mating coat from April to August, resting from August to March), the birds reach the fourth, exceptionally in the third or fifth year of life. Chicks from the top are buffalo or light brown, varyingly black-stained or mottled. Forehead and throat, brown-black, breast and white belly. Dark brown iris, brown to orange beak, with a distinct black end. Pink or orange-orange legs. Teenage robe (from acquiring the bird’s ability to fly, i.e. from July to October), is very similar to the resting plumage of adult birds. The common tern speaks out loud “krii”, “krre”.
Where raises the young?
It is a small and poorly disseminated species. In the central and eastern part of the country, it is mainly associated with larger rivers, primarily the valleys of the Vistula, Bug, Narew and Warta rivers, which inhabits over 60% of the breeding population. It most often occurs in the middle section of the Vistula, between the mouth of San and Włocławek. In the southern and south-western part, where the watercourses are few and regulated (no sandy banks in the current), the common tern nestles on ponds and artificial water reservoirs, with distinct clusters in the Barycz Valley (Milicz Ponds) and the Upper Vistula Valley (Goczałkowicki Reservoir) ). In the mountains, single pairs were recorded in the Western Carpathians, on the Dunajec.
The common tern is nested in sea and coastal areas as well as inland – on lakes, fishponds, artificial water reservoirs, gravel pits and river valleys, on natural and artificial islands and peninsulas. It prefers flat pebble and sandy beaches, choosing places with low and not very dense vegetation or with a large number of shells, where the chicks can hide. He does not shy away from pastures, salty swamps, moors and rocky islands. In particular, it avoids cold water, steep areas or exposed to high winds and rainfall, as well as densely overgrown, which prevent the movement of the chicks. The choice of habitat by river tern determines the presence of relatively large feeding grounds – stagnant or flowing waters rich in small fish. They can nest individually, in small groups of several or several pairs or in large, compact and dense colonies of several hundred, and exceptionally even over one thousand couples He also eagerly settles in homogeneous, single-species groups, and creates mixed colonies with other terns.
How does he live?
A tern nest is a shallow hole in the ground, in sand or gravel, usually among low, rare vegetation. It is a delicate and durable construction, improved and added during incubation, without lining or scantily lined at the bottom and edges with material brought from the neighborhood. It is built on sand, without any cover, sometimes covered by the wind. In the absence of islands on lakes and artificial water reservoirs, this bird assumes a nest on a floating pleat (a sheepskin coat with plants on the water surface), reed cuts, fragments of trees protruding from the water, possibly on dikes. Common tern is strongly associated with the place of hatching and nesting, about 65% of the chicks return to their native breeding grounds.
How does he live?
The common tern leads a daily lifestyle, wintering mainly in western and southern Africa, less frequently in Portugal and southern Spain. Birds ringed in Poland in the winter spend on the Atlantic coast of Africa, from Morocco in the north to the southern ends of the continent. It comes to breeding grounds in April. It nests once a year, but depending on the environmental conditions, first of all on the availability of food near the breeding grounds, the deadline for laying eggs may vary. On the islands of the central Vistula, the breeding season starts in the last decade of April, and the peak of laying eggs usually falls in the second half of May. The large Vistula gear and unfavorable weather in May (low temperature and heavy rains) may delay the breeding season.
The eggs are incubated by both parents, however, the female is given more time, which during the egg laying and at the beginning of the incubation is fed by the partner. The young are hatching covered and can see at once. The nest may leave after a few hours, but for the first few days of their life they must be warmed up by their parents, and after acquiring the ability to fly, they also have to learn how to independently obtain food. They get their full independence only after 2-3 months of life. They ripen sexually most often in the third year of life.
The common tern is a digestive opportunist, depending on the situation, it can quickly change both the way of feeding and the type of food. The main components of the diet are fish, crustaceans, ringlets, snails and insects. Fish, river terns most often dive from the flight, they also regularly feed from “catch up”, looking for fish from above, sitting, for example, on a bridge, breakwaters, etc.
- Sikora A., Mikusek R. 2004. Sterna hirundo (L., 1758) – rybitwa rzeczna. W: Gromadzki M. (red.) Ptaki (część I). Poradniki ochrony siedlisk i gatunków Natura 2000 – podręcznik metodyczny. Ministerstwo Środowiska, Warszawa. T. 7, s. 186-191.
- Bukaciński D., Bukacińska M., Betleja J. 2015. Rybitwa rzeczna Sterna hirundo, Ślepowron Nycticorax nycticorax W: Chylarecki P., Sikora A, Cenian Z., Chodkiewicz T. (red.) Monitoring ptaków lęgowych. Poradnik metodyczny. Wydanie 2. GIOŚ, Warszawa, s.299-305; 354-358.