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Tern

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Terns are a diverse group of seabirds within the subfamily Sterninae. They belong to the larger family Laridae, which also includes gulls and skimmers.

Birds of Sweden 2016 08
Birds of Sweden 2016 08

These birds have a worldwide distribution. You can find them near oceans, rivers, or wetlands. Terns are known for being slender and lightly built. They have long, narrow wings and long, pointed bills. Most species feature pale grey feathers on their upper bodies and white feathers below. They often wear a contrasting black cap on their heads.

This specific coloring serves a purpose during hunting. The white underparts help the bird stay hidden from fish looking up toward the sky.

The physical structure of a tern is designed for elegant flight. Their long, narrow wings and long tails make them very streamlined.

White tern with fish
White tern with fish

Many sea terns possess deeply forked tails, while other species have at least a shallow V-shape. The noddies, a specific genus called Anous, have even more unusual notched-wedge shaped tails. While their legs are relatively short, terns are actually capable of running well. They have webbed feet, but they rarely swim. Usually, they only land on the water to bathe.

Terns go through several distinct stages of feather growth, known as plumage. Juvenile birds look quite different from adults. They often have brown or yellow-tinged upperparts with dark edges that create a scaly appearance.

They also have dark bands on their wings and shorter tails. Most species do not begin their first major moult, which is the process of shedding old feathers, until after migration. By their second summer, they look much more like adults. They usually reach full mature plumage by their third year. After the breeding season, they moult into a non-breeding plumage, which typically includes a white forehead.

There is a wide variety of tern species with different appearances. Terns range significantly in size. The least tern is very small, weighing only about 33 grams.

Yellow-billed tern Sternula superciliaris
Yellow-billed tern Sternula superciliaris

In contrast, the Caspian tern is much larger, reaching 1.5 kilograms.

Sterna-caspia-010
Sterna-caspia-010

Some species have very dark plumage instead of the typical grey and white. The Inca tern is a notable example of this atypical dark plumage.

Larosterna inca4
Larosterna inca4

Other species, like the black tern or the black-bellied tern, show black underparts during the breeding season. Scientists suggest that dark plumage in tropical areas might make it harder for other birds to detect them while they feed.

Humans have studied and named terns for centuries. The word "stearn" appeared in Old English as early as the eighth century. It even appears in the ninth-century poem "The Seafarer."

Large-billed Tern (Phaetusa simplex), Pantanal, Brazil
Large-billed Tern (Phaetusa simplex), Pantanal, Brazil

In 1758, the scientist Linnaeus formally recognized the distinction between gulls and terns. He placed terns in the genus Sterna. He described them as "rostrum subulatum," which means they have an awl-shaped bill. This refers to their long, pointed bills that distinguish them from the thicker-billed gulls.

Terns use a wide repertoire of vocalizations to communicate. For example, the common tern has a distinctive alarm call described as "kee-yah."

Gull-billed Tern in Koonthalulam, India, by Dr. Tejinder Singh Rawal
Gull-billed Tern in Koonthalulam, India, by Dr. Tejinder Singh Rawal

They also use a shorter "kyar" call when taking flight due to a threat. This sound helps quiet a noisy colony so residents can assess danger. Parents and chicks use specific calls to locate one another. Even siblings can recognize each other's unique voices about twelve days after hatching. These vocal differences also help humans distinguish between very similar species, such as the common and arctic terns.

While terns are long-lived and generally free from many natural predators, they face modern challenges. Most species are currently declining in number due to human activities. These activities include habitat loss, pollution, and disturbance. Introduced mammals also pose a threat through predation. The Chinese crested tern is currently classed as critically endangered.

2020-07-18 Thalasseus sandvicensis, St Marys Island, Northumberland 01
2020-07-18 Thalasseus sandvicensis, St Marys Island, Northumberland 01

Although international agreements offer some protection, adults and eggs are still sometimes used for food in tropical regions. Understanding the complex relationships between tern genera through DNA research continues to help scientists map their history.

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🖼️ Images & Media (20)
File:Birds of Sweden 2016 07.jpg
Birds of Sweden 2016 07.jpg
File:Birds of Sweden 2016 08.jpg
Birds of Sweden 2016 08.jpg
File:Larosterna inca4.jpg
Larosterna inca4.jpg
File:White tern with fish.jpg
White tern with fish.jpg
File:Anous minutus by Gregg Yan 02.jpg
Anous minutus by Gregg Yan 02.jpg
File:Sterna fuscata.JPG
Sterna fuscata.JPG
File:Yellow-billed tern Sternula superciliaris.jpg
Yellow-billed tern Sternula superciliaris.jpg
File:Large-billed Tern (Phaetusa simplex), Pantanal, Brazil.jpg
Large-billed Tern (Phaetusa simplex),...
File:Sterna-caspia-010.jpg
Sterna-caspia-010.jpg
File:Gull-billed Tern in Koonthalulam, India, by Dr. Tejinder Singh Rawal.jpg
Gull-billed Tern in Koonthalulam, India,...
File:Larosterna inca3.jpg
Larosterna inca3.jpg
File:White-winged Tern, Mścichy, Biebrzański Park Narodowy, Polska.jpg
White-winged Tern, Mścichy, Biebrzański...

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