Forest Tern

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Forest Tern
Adult forest tern (Sterna forsteri) in breeding plumage

Adult forest tern ( Sterna forsteri ) in breeding plumage

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Terns (Sternidae)
Genre : Sterna
Type : Forest Tern
Scientific name
Sterna forsteri
Nuttall , 1834
Adult forest tern in a simple dress
Flying forest tern in breeding plumage

The forest tern ( Sterna forsteri ) is a species of bird from the tern family (Sternidae). Their distribution area covers large parts of North America with some large and numerous smaller, scattered occurrences . The occurrence outside the breeding season is also largely limited to this continent, including the West Indies .

The forest tern was named in honor of the German naturalist Johann Reinhold Forster . The species is sometimes found under the name of the swamp tern . However, this is not clear, as the species of the genus Chlidonias are also referred to as "swamp terns".

description

With a body length of 33–36 cm, a wingspan of 73–82 cm and a weight of 130–190 g, the forest tern is one of the medium-sized species of tern. It resembles the common tern , but is larger and shorter-winged than the common tern , with a relatively larger head, a stronger, dagger-like beak, and longer legs. As with the arctic tern, the tail spikes tower above the wings of the seated bird. The genders do not differ externally.

In adult birds in the breeding plumage , the approximately 39 mm long bill is orange-red with a black tip, which extends over 15-25 mm on the upper beak. The forehead, upper reins, crown and neck are black and form a head cap that extends just below the eye. The lower rein between the cleft beak and the cap is 3–6 mm wide and white. This part is widest in the middle of the reins. The lower sides of the head and neck are pure white like the rest of the underside. The upper side is predominantly light blue-gray and usually a little lighter gray than that of the common tern. The rump is white and contrasts with the gray back. Upper tail coverts and control feathers are predominantly light gray like the back. The control springs also have diffuse white hems. Only the two outer pairs are white at the tip and outer flag and are clearly elongated overall. In the fresh plumage, the hand and arm wings are silvery white and slightly lighter than the upper wing-coverts. The arm wings are broadly lined with white on the inside flag and tip. On the inner wings of the hand these white seams are a little narrower. The inner flags of the outer hand wings are matt gray with a silvery white shaft line and a light gray wedge at the base. The light gray hand covers are lightened white towards the tip. The wing leading edge is like the axillary feathers and the under wing coverts white. The legs and feet are orange-red.

The plain dress of adult birds resembles the brood dress except for the head markings, beak and feet. The beak is black; sometimes you can still see a somewhat red to reddish-brown color at the base. The head is white and shows a characteristic black mask that extends from in front of the eye over the ear covers. The nape of the neck is gray-white and sometimes speckled diffusely dark. The parting can be finely and darkly dashed, especially towards the back of the head. Legs and feet are reddish brown to reddish orange.

distribution

The breeding distribution of the forest tern is limited to North America. It is divided into several disjoint sub-areas and scattered occurrences. The largest is in the Prairie Pothole region . In Canada it stretches from southeast Alberta east over the southern half of Saskatchewan and southwest Manitoba north to Lake Winnipeg , in the United States over the eastern half of North Dakota , the northeast of South Dakota , the west and the southern center of Minnesota and the northern center Iowas .

A second sub-area is located southwest of it in the northern part of the Great Basin . It stretches from central southern Washington through northeast and southern Oregon , northeast California, and northern Nevada to northern Utah . There are other occurrences in the extreme south of British Columbia , in the western center, the southern coastal areas and in the southeast of California, in the north of Baja California Norte , in southern Idaho , scattered over Montana and Wyoming , in the southern center of South Dakota and in the west Nebraskas as well as in central Kansas .

In the Great Lakes area, the forest tern breeds in eastern Wisconsin , in the extreme north of Illinois , in eastern Michigan and in the extreme south of Ontario . On the Atlantic coast, it breeds in Massachusetts , southern New York , New Jersey , Delaware , Maryland , Virginia, and North and South Carolina . On the Gulf Coast, it breeds in Tamaulipas , Texas , southwest and southeast Louisiana, and southern Alabama .

hikes

The forest tern is a short- or medium-distance migrant, which completely clears the breeding areas in the north and those inland in the winter months and can then be found in the coastal regions of subtropical North America as well as the coasts and inland waters of Central America. This year's birds initially disperse in a north and south direction towards the end of the breeding season. The following year they spend the summer in their winter quarters.

The wintering areas extend in the west from the Pacific coast of California via Baja California and along the Sierra Madre Occidental and Sierra Madre del Sur to El Salvador . As a rare winter visitor, the species is found up to Panama . In the east, the winter distribution extends from the extreme south of New Jersey along the Atlantic coast south, across Florida, on the Gulf of Mexico also far into the inland and in Mexico to the coasts of the Yucatán Peninsula . In inland Mexico, the species from Durango and San Luis Potosí westward to Chiapas is a regular winter visitor. It winters in small numbers in Bermuda , rarely in the Bahamas , Cuba and the Cayman Islands, and very rarely in Hispaniola , Puerto Rico and the Virgin Islands .

The autumn migration usually begins in August and continues until mid-October. In spring the birds break out in their winter quarters from March; from April the first arrive in the breeding areas in the temperate latitudes. At the end of May the train is largely completed.

habitat

The forest tern breeds in fresh, brackish and salt water swamps as well as on marshy lake, island and river banks. It mainly inhabits open and deeper wetlands with open water bodies, island-like vegetation and large-scale floating leaf vegetation . In Iowa, it only accepts swamps over 20 hectares as breeding habitat. On the Atlantic coast they can be found on swampy stretches of beach and in estuary areas . The habitats are often subject to strong changes from year to year and are therefore quite short-lived.

nutrition

The forest tern feeds primarily on fish up to 10 cm in size. Various invertebrates are also used as food. The prey fish identified included Cymatogaster aggregata , American anchovies ( Engraulis mordax ), Clevelandia ios , American perch , Notropis sp., Pike and sticklebacks .

Typically, it flies on patrol at a height of 6–8 m over swamps and lakes, canals or coastal areas and prey on its food by diving. To do this , it shakes briefly above the water and then thrusts down, mostly only partially immersing it, but sometimes catching animals up to 30 cm deep. Sometimes she uses posts, bridges, telephone wires or boats as a hide.

Reproduction

When young forest terns breed for the first time is unknown. This is likely not the case until the age of two. There is an annual brood; Replacement clutches after losing the first brood are not uncommon. The species is presumably monogamous; nothing is known about the length of the couple's relationship.

The forest tern breeds individually or in colonies of usually less than 100 pairs, but the largest consisted of over 2,750 nests. The colonies are occupied between mid-April and mid-May. During this time or shortly thereafter, the pairs also form, with courtship flights over the colony playing an important role. Later, courtship takes place more on the ground, for which an average of about 2 m² is defended against other individuals. Important elements of the floor courtship are the “parades” in which the partners run alongside each other and do the courtship feeding. Later copulation occurs regularly.

The nest is built on the ground or on the water and can consist of a simple hollow or a small bowl made of marsh grasses, as well as a floating platform made of plant parts with an average diameter of about 30 cm. In inland swamps it usually stands on muskrat castles or carpets of floating plants. Often old nests are used by racing or binding divers as a source of material, rarely used directly or usurped. Sometimes the species also nests on gravel banks of river islands, where the nests are on the bare ground or in the pioneer vegetation. Artificial brood rafts are also accepted.

The egg-laying time begins at the beginning of May and sometimes lasts until July. The clutch usually consists of three, sometimes two, more rarely one, four or even six eggs of about 43 × 31 mm in size and a matt surface, which are irregularly spotted dark brown on an olive-colored to yellowish beige or pinkish beige background. The incubation begins with the first egg and lasts between 23 and 28 days. Both parents brood. Now only the nest and its immediate surroundings are defended against other birds.

After hatching, young forest terns are, as is typical for those who flee from the nest , very well developed and can already walk. However, they only leave the nest permanently after 2–7 days. They are able to fly after 4–5 weeks.

Duration

No information is available on the total population of the forest tern. According to inventory surveys, the population in Canada amounts to 2133–4216 breeding pairs, those in the Great Lakes area to 3025 pairs in 45 colonies, those on the Atlantic coast to 5766, those of the Gulf coast to 23,069 pairs. 8,095 individuals were counted on the US Pacific coast and 30–35 pairs in Baja California.

There is no information on inventory trends. The species is not considered endangered ( least concern ) by the IUCN .

literature

Individual evidence

  1. ↑ Mcnicholl et al. (2001), section Systematics , see literature
  2. ↑ a b c Mcnicholl et al. (2001), section Distinguishing Characteristics , see literature
  3. ↑ a b c Olsen / Larsson (1995), pp. 103-110, see literature
  4. ^ Lars Svensson, Peter J. Grant, Killian Mullarney, Dan Zetterström: Der neue Kosmos Vogelführer . Kosmos, Stuttgart, 1999, ISBN 3-440-07720-9 , pp. 190-191
  5. ↑ a b c d Mcnicholl et al. (2001), section Distribution , see literature
  6. ↑ a b Mcnicholl et al. (2001), Migration section , see literature
  7. ↑ Mcnicholl et al. (2001), Habitat section , see literature
  8. ↑ a b Mcnicholl et al. (2001), section Food Habits , see literature
  9. ↑ a b Mcnicholl et al. (2001), section Demography and Populations , see literature
  10. ↑ a b c Mcnicholl et al. (2001), Behavior section , see literature
  11. ↑ John A. Hall: Aspects of Forster's Tern (Sterna forsteri) Reproduction on Cobblestone Islands in Southcentral Washington , Northwest Science, Vol. 63, No. 3, 1989, pp. 90-95 ( PDF )
  12. ↑ a b c Mcnicholl et al. (2001), section Breeding , see literature

Web links

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