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Discover the Fascinating World of the Antarctic Tern: From Plumage to Migration

Antarctic Tern, Sterna vittataThe Antarctic Tern is a small migratory seabird that spends its summer breeding season in Antarctica and its winter in the South Atlantic. This bird is a member of the family Laridae, which includes gulls, terns, and skimmers.

The Antarctic Tern is a fascinating creature that has a unique natural history and interesting behaviors. In this article, we will explore the identification, plumages, molts, and other important aspects of this species to gain a better understanding of this captivating bird.

Identification

The Antarctic Tern is characterized by its white plumage, with black caps on its head and red-orange bills, feet, and legs. The black cap extends down to the birds eyes, giving it a distinctive appearance.

This tern has an overall length of 36-41 centimeters, making it a relatively small species. Its wingspan ranges from 76-80 centimeters.

The birds weight varies from 92-138 grams. Field

Identification

The Antarctic Tern can be easily identified in the field by its distinctive black cap and red-orange bill, feet, and legs.

This terns white plumage is also a good field mark. Its wings are long and slender, with a pointed tip.

This feature distinguishes it from gulls, which have broader wings. The Antarctic Tern has a graceful flight style, with steady wing beats and occasional gliding.

Similar Species

The Antarctic Terns black cap is a key field mark that distinguishes it from other terns, such as the Arctic Tern and Common Tern, which have gray caps. The South American Tern, which is found in the same range as the Antarctic Tern, has a similar appearance.

However, this tern has a dark red bill and darker underwings. The smaller size of the Little Tern and Least Tern also distinguishes them from the Antarctic Tern.

Plumages

The Antarctic Tern, like most gulls and terns, undergoes two distinct plumages – breeding and non-breeding. The breeding plumage is more colorful and distinctive than its non-breeding plumage.

In breeding plumage, the Antarctic Terns bill and feet turn a bright red-orange color. This color change signals to other birds that the tern is ready to breed.

The birds also develop a black cap on their heads that extends down to the eyes. The back and wings of breeding birds are also darker than those in non-breeding plumage.

In non-breeding plumage, the Antarctic Terns bill and feet are paler in color. The black cap also fades, and the back and wings become lighter.

This plumage is less distinctive than the breeding plumage.

Molts

Like most birds, the Antarctic Tern undergoes a series of molts throughout its life. Molting is the process of shedding old feathers and growing new ones.

The molting process can be divided into six stages: pre-basic, basic, pre-alternate, alternate, pre-formative, and formative.

The pre-basic molt is when the bird replaces worn-out flight feathers, body feathers, and coverts after the breeding season.

The basic molt occurs in non-breeding birds and is the replacement of all feathers except the flight feathers. Pre-alternate molt begins as the breeding season approaches and is when the bird begins to grow its breeding plumage.

The alternate molt is the replacement of all non-flight feathers in the breeding season and is when the bird achieves its colorful and distinctive breeding plumage. Pre-formative molt occurs in young birds and is when they replace their down feathers with juvenile feathers.

The formative molt is when juvenile feathers are replaced with adult feathers.

Conclusion

The Antarctic Tern is a unique and fascinating bird species with distinctive physical features and plumages. Its black cap and red-orange bill, feet, and legs make it easy to identify in the field, while its graceful flight style is a joy to watch.

The molting process is an essential part of the bird’s life cycle, and understanding it helps us appreciate this species better. Whether breeding in the frozen expanses of Antarctica or foraging in the South Atlantic, the Antarctic Tern is a remarkable seabird to behold.

, as the information will speak for itself.

Systematics History

The Antarctic Tern, Sterna vittata, is a member of the family Laridae that includes gulls, terns, and skimmers. The species was first described by John Gould in 1841 based on specimens collected from Antarctic expeditions.

Over the years, there have been changes and updates to the taxonomy of the species.

Geographic Variation

The range of the Antarctic Tern is primarily confined to the Southern Hemisphere. The species breeds on the coastlines of Antarctica, the Falkland Islands, South Georgia, and the South Sandwich Islands.

During the non-breeding season, the birds disperse northward along the South American coast up to Peru and North Carolina in the United States. The species has a circum-Antarctic distribution.

However, there are geographic differences in size and plumage coloration across its range. These variations have led to the recognition of subspecies within the species.

Subspecies

The scientific name of the Antarctic Tern, Sterna vittata, refers to a distinctive feature of the species, the black crown stripe. This characteristic is more pronounced in some populations, leading to the recognition of subspecies.

There are two recognized subspecies of Antarctic Tern:

1. Sterna vittata vittata – Breeds on the Antarctic Peninsula, South Shetland Islands, and South Orkney Islands.

This subspecies is the smallest of the two and has a shorter bill compared to the other subspecies. 2.

Sterna vittata georgiae – Breeds on South Georgia, the South Sandwich Islands, and the Falkland Islands. This subspecies has a larger bill and a more extensive black crown stripe.

Related Species

The Antarctic Tern is part of a group of terns known as the “water terns.” These birds consist of several species that breed on coasts and islands in the Southern Hemisphere. All water terns, including the Antarctic Tern, have a black cap and brightly colored bills, feet, and legs.

The Antarctic Tern is most closely related to the South American Tern, Sterna hirundinacea. These two species are similar in appearance, and their ranges overlap in the South Atlantic.

However, the South American Tern is slightly larger than the Antarctic Tern and has a darker red bill.

Historical Changes to Distribution

The Antarctic Tern’s distribution and abundance have been affected by several factors, including climate change, human disturbance, and whaling. The species has undergone significant range changes over the past two centuries.

During the 18th and 19th centuries, whaling and sealing expeditions often recorded sightings of Antarctic Terns. However, by the early 1900s, hunting had severely depleted whale populations, and the terns that depended on them for food suffered as well.

By the mid-1900s, Antarctic Terns were considered scarce in many parts of their range due to changes in the availability of prey. In recent years, the Antarctic Tern’s range has expanded to new areas, possibly due to changes in prey availability and climate patterns.

In the Southern Hemisphere, warming ocean and air temperatures are leading to changes in the distribution of prey, which could be driving range shifts in the species. In South Georgia, where the species has one of its largest breeding populations, there has been a decline in breeding success due to human disturbance from the increasing number of tourism activities.

Scientists are studying the effects of these activities on the behavior and nesting success of the Antarctic Tern and other seabirds.

Conclusion

The Antarctic Tern is a remarkable seabird species that inhabits one of the most inhospitable regions of the world. The species displays geographic variation in size and plumage, leading to the recognition of subspecies.

The Antarctic Tern is closely related to other water terns and has undergone significant range changes over the past two centuries. While climate change and changes in prey availability may be driving range shifts, human disturbance from tourism activities is threatening breeding success in some areas.

Understanding the systematics history and distribution changes of the species can inform conservation efforts and help protect this unique seabird. , as the information will speak for itself.

Habitat

The Antarctic Tern is a seabird species that is found primarily in the Southern Hemisphere. During the breeding season, these birds are found in Antarctica, the South Sandwich Islands, South Georgia, and the Falkland Islands.

The species prefers to nest on exposed rock ledges or gravel beaches in open areas near the sea. Antarctic Terns feed primarily on fish and krill.

They forage in near-shore waters and over estuaries, and occasionally dive in shallow water to catch their prey. During the winter, they disperse northward along the South American coast up to Peru and North Carolina in the United States.

Movements and Migration

The Antarctic Tern is a migratory seabird. During the breeding season, population concentrations are found in Antarctica, South Georgia, and the South Sandwich Islands.

After the breeding season ends, the adults disperse to wintering areas along the South American coast. The migration pattern of the Antarctic Tern is unique in that it migrates to areas of upwelling, where nutrient-rich waters provide abundant food for the birds.

These areas are characterized by cooler water temperatures and are located along the western coasts of South America and the eastern coasts of North America. Recent studies have shown that the migration patterns of the Antarctic Tern are changing.

As ocean temperatures continue to rise due to climate change, the distribution and abundance of prey are also changing. This could alter migration patterns of the species and lead to changes in its distribution.

In addition to migratory movements, Antarctic Terns also engage in regional movements during the breeding season. These movements are related to variations in prey availability.

For example, during years of low krill availability, the birds may move to other breeding locations in search of more plentiful food. Antarctic Terns are also known for their long-distance movements.

Studies have shown that some birds travel over 14,000 km during their annual migrations, making this species one of the most migratory of all seabirds.

Conclusion

The Antarctic Tern is a migratory seabird that is found primarily in the Southern Hemisphere. The species breeds in Antarctica, the South Sandwich Islands, South Georgia, and the Falkland Islands, and migrates northward along the South American coast during the winter.

The birds engage in regional movements during the breeding season, and some individuals engage in long-distance movements of over 14,000 km. Changing climate patterns and prey availability could alter the migration patterns and distribution of this species in the future.

Understanding the movements and habitat requirements of the species is essential for effective conservation efforts, which can help protect this remarkable seabird. , as the information will speak for itself.

Diet and Foraging

The Antarctic Tern is a seabird species that feeds primarily on fish and krill. The species forages in near-shore waters and over estuaries, and occasionally dives in shallow water to catch prey.

The birds are capable of flying long distances in search of food.

Feeding

Antarctic Terns are active feeders that forage during the day and feed their young during the breeding season. During the non-breeding season, the birds disperse northward along the South American coast up to Peru and North Carolina in the United States.

The species engages in a variety of feeding behaviors to obtain food. The birds typically forage in small groups or individually, using sight and hearing to locate prey.

They are also known to follow fishing vessels, where they scavenge for scraps of discarded fish. Antarctic Terns use a variety of feeding techniques, including plunge-diving, surface dipping, and aerial pursuit.

Plunge-diving is the most common technique, where the birds hover over the water before diving head-first into the water to catch prey. In surface-dipping, the bird skims the surface of the water and dips its bill to catch prey.

In aerial pursuit, the bird hovers over the water and swoops down to catch its prey.

Diet

Antarctic Terns feed primarily on fish and krill. The species has a varied diet that includes small fish, squid, and crustaceans.

In the Antarctic Peninsula, the bird’s diet is dominated by krill, while in South Georgia, the diet is more diverse and includes fish species such as Atlantic Salmon and Sand Eels. The species has a high metabolic rate and requires a constant supply of food to maintain its energy levels.

During the breeding season, the adults feed their young with small fish and crustaceans. As the chicks grow, their diet shifts to larger prey items such as squid.

Metabolism and Temperature Regulation

Antarctic Terns have a high metabolic rate, which allows them to fly long distances and sustain high levels of activity. The species has a unique ability to maintain an elevated metabolic rate, even in cold environments.

This is achieved through a combination of insulation from their feathers and a high metabolic rate, which generates internal heat. The birds are also capable of regulating their body temperature by altering their posture and using thermoregulatory mechanisms.

When temperatures are cold, the birds huddle together and tuck their bills into their feathers to reduce heat loss. When temperatures are warm, they spread their wings and legs to increase heat loss.

Overall, the Antarctic Tern has evolved to thrive in the harsh environments of the Southern Ocean, where food is not always plentiful, and temperatures can be extreme.

Sounds and Vocal

Behavior

Antarctic Terns are vocal birds that use a variety of calls and vocalizations to communicate. The species has a repertoire of vocalizations that is used to reinforce social bonds, defend territories, and attract mates.

Vocalization

The most common call of the Antarctic Tern is a shrill, high-pitched scream that is used during aggressive encounters and to alert other birds to the presence of danger. The species also makes a variety of other calls, including a harsh, grating call that is used in defense of territory.

During courtship, the male bird makes a soft, whistling call to attract a mate. Antarctic Terns are also capable of producing complex vocalizations that are used to reinforce social bonds.

These calls consist of low-frequency sounds that are produced in the bird’s syrinx, and they are thought to be unique to each individual bird. Overall, the vocalizations of the Antarctic Tern are an important aspect of the species’ social behavior and communication.

By understanding the birds’ vocalizations, scientists can gain insights into their behavior, ecology, and evolution. , as the information will speak for itself.

Behavior

The Antarctic Tern is a social and relatively active seabird species. The birds engage in a variety of behavior patterns, including locomotion, self-maintenance, agonistic behavior, and sexual behavior.

Locomotion

The Antarctic Tern has a graceful and buoyant flight style, characterized by rapid, shallow wing beats and occasional gliding. The species can fly long distances in search of food or during migration.

The birds are also capable of swimming and diving to catch prey.

Self Maintenance

The birds engage in various forms of self-maintenance behavior. They preen their feathers to maintain their insulation and waterproofing, and use their beaks and feet to remove parasites from their feathers.

The birds also bathe in water to remove dirt and oil from their feathers. Agonistic

Behavior

Antarctic Terns engage in a variety of agonistic behavior patterns, particularly during the breeding season.

The birds defend their territories through aggressive behavior, such as chasing and aerial attacks against intruders. They use a variety of vocalizations and body postures to communicate with other birds and signal their intentions.

Sexual

Behavior

During the breeding season, the male Antarctic Terns establish territories and court females by performing displays and vocalizations. The males engage in aerial displays that involve hovering, calling, and swooping.

The female selects a mate based on the quality of their territory and display.

Breeding

The Antarctic Tern is a monogamous species that breeds during the austral summer. The birds form pairs during the breeding season and engage in courtship behavior.

After copulation, the female bird usually lays one to two eggs in a scrape on the ground, often lined with vegetation. Both parents take turns incubating the eggs and caring for the young.

During incubation, the adults huddle together to keep warm and protect the eggs from the cold. After hatching, the chicks are fed regurgitated fish and krill by both parents, who take turns to forage for food.

Chicks fledge after 20-30 days, once they are able to fly and feed themselves. The breeding cycle of the Antarctic Tern is relatively short, with birds leaving their breeding sites soon after chicks fledge.

Demography and Populations

The global population of the Antarctic Tern is estimated to be around 50,000-100,000 individuals. The species is considered to be stable, although some local populations may be declining due to human disturbance and loss of habitat.

The bird’s breeding range is limited to the Southern Hemisphere, where it breeds in Antarctica, the South Sandwich Islands, South Georgia, and the Falkland Islands. The species disperses northward along the South American coast during the non-breeding season.

Monitoring the demography and

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