Bird O'clock

Discover the Graceful Flight and Remarkable Behavior of the Aleutian Tern

The Aleutian Tern, Onychoprion aleuticus, is a small, migratory bird that breeds in the Aleutian Islands of Alaska and winters along the west coast of Mexico and Central America. This striking bird has a sleek and slender body that measures around 12-14 inches in length and has a wingspan of 25 inches.

In this article, we will discuss the field identification, plumages, and molts of the Aleutian Tern.

Identification

The Aleutian Tern is easily identifiable by its sleek and slender body with grey upperparts, white underparts, and black cap and nape. The bill and feet are black, and the eyes are dark brown.

During breeding season, the black on the head extends further down the neck. In flight, the bird shows a distinctive forked tail with dark wingtips.

The tern has a distinctive call that sounds like a high-pitched klee-err or kih-luh. Field

Identification

To identify the Aleutian Tern, observers should look for the bird’s small size, sleek body shape, forked tail, dark wingtips, black cap and nape, and white underparts.

When flying, the bird’s wings appear long and slender, and they row through the air with a distinctive, graceful, and effortless flight pattern. This bird’s dark bill and feet contrast its pale body.

It breeds in locations where other tern species are absent.

Similar Species

The Aleutian Tern can be easily confused with other tern species, namely the Arctic Tern and the Common Tern. Still, it has several characteristics that distinguish it from these species.

The Arctic Tern has a long, slender tail, while the Common Tern has more black in its head and a shorter bill that is more orange in color. Compared to these two species, the Aleutian Tern’s tail has a more noticeably deeper fork.

Plumages

The Aleutian Tern has two plumages: breeding and non-breeding. The breeding plumage is more striking, with a jet black cap and nape that extends to the back of the neck.

During non-breeding season, the black cap and nape are dull, and the bird’s white forehead has conspicuous dark markings. Its wings and upperparts are uniform gray, and the head, neck, and throat are white.

The underparts are white without any markings.

Molts

The Aleutian Tern has two molts in a year. The first molt takes place during late summer to early fall, and the second occurs from late winter to early spring.

During the first molt, the bird sheds its feathers and grows new ones. In the second molt, the bird replaces its flight feathers.

In conclusion, the Aleutian Tern is a migratory bird that can be easily identified by its sleek and slender body, forked tail, and black cap and nape. The bird has two plumages, breeding and non-breeding, and two molts in a year.

Field identification and awareness of similar species help in distinguishing the Aleutian Tern from other terns. Those lucky enough to spot an Aleutian Tern are sure to experience the sight of a graceful and magnificent bird.

Systematics History

The Aleutian Tern, Onychoprion aleuticus, is a species of tern that belongs to the family Laridae. The bird was first described by William Stimpson in 1857.

In the past, it was considered a subspecies of the Sandwich Tern (Sterna sandvicensis), but studies in the 1990s revealed that it was a distinct species.

Geographic Variation

The Aleutian Tern is primarily found in the Aleutian Islands of Alaska. This bird is unique as it breeds in areas where most other tern species are absent.

While it primarily breeds in the Aleutian Islands, it can also be found in Kamchatka, Russia, and occasionally in Japan. During winter, the Aleutian Tern migrates southward to the west coast of Mexico and Central America.

Subspecies

The Aleutian Tern has no recognized subspecies, but there is some geographic variation in its appearance. Birds found in eastern areas of the Aleutian Islands have a slightly larger bill and a darker crown than those found in western areas.

However, these differences are not considered significant enough to warrant subspecies status.

Related Species

The Aleutian Tern is closely related to other tern species in the genus Onychoprion, including the Bridled Tern (Onychoprion anaethetus) and the Gray-backed Tern (Onychoprion lunatus). These species share similar body shapes and behaviors, and they breed in tropical and subtropical regions around the world.

The Aleutian Tern’s closest relative is the Cabot’s Tern (Onychoprion anaethetus eurygnathus), which is found in the Caribbean and the Gulf of Mexico.

Historical Changes to Distribution

The historical distribution of the Aleutian Tern is difficult to determine due to its remote breeding locations and the limited scientific attention it has received. However, it is known that the bird’s range has expanded over time.

Historical records show that the bird was rarely sighted in coastal Alaska until the 1970s, when their numbers began to increase. One significant historical change in distribution occurred in 1980 when an American oil tanker, the SS Texaco North Dakota, ran aground near Unalaska Island in the Aleutian chain.

This accident resulted in an oil spill that affected the entire breeding colony of Aleutian Terns in the area. Researchers monitoring the colony before and after the spill found that the population declined significantly following the spill, indicating the vulnerability of this species to human disturbance.

Another significant historical change in distribution occurred in the late 1980s, when a group of Aleutian Terns began nesting on the mounds of abandoned sea otter pelts on the southern coast of the Alaska Peninsula, which was outside of their known breeding range. The reason for this change is unclear, but it may be due to a lack of suitable nesting sites in their traditional range.

In recent years, the Aleutian Tern’s range has continued to expand, with the bird now breeding in areas as far east as False Pass and Umnak Island in the Aleutian chain. This expansion has been attributed to climate change, which has created more favorable conditions for the bird’s prey.

In Conclusion, the Aleutian Tern is a unique and fascinating bird species that breeds in the remote Aleutian Islands of Alaska. The bird’s geographic variation, lack of subspecies, and close relation to other tern species illustrate its distinctiveness.

The historical changes to the bird’s distribution, including oil spills and range expansion, demonstrate the species’ vulnerability and resilience to human activity and environmental change. While we continue to learn more about this species, it is important to protect their fragile breeding grounds and monitor their populations to ensure their continued survival.

Habitat

The Aleutian Tern is a bird species that prefers a marine habitat near the coastlines of the Aleutian Islands, Alaska. These birds breed in the remote Aleutian Islands, where they construct their nests on rocky cliffs, slopes, or low-lying islands.

They typically choose nesting sites that are near their primary food source, which is fish and invertebrates. The bird is known to use habitat features like rocks, gravel, and seaweed to build their nests.

The Aleutian Tern shares its habitat with other bird species like the Tufted Puffin and the Horned Puffin. Outside of the breeding season, the bird moves to the open waters of the Northern Pacific coast and migrates to the West coast of Mexico and Central America.

Movements and Migration

The Aleutian Tern is a migratory species and travels between breeding and non-breeding habitats usually twice a year. The bird’s migration path takes it on a long journey from its breeding sites in Alaska to its wintering grounds along the west coast of Mexico and Central America.

The Aleutian Tern starts its southward migration in August by moving from its breeding grounds in Alaska to Western British Columbia, Canada. Together with other waterbirds, they move along the Pacific coast, stopping in areas where their prey is abundant.

Eventually, they reach their wintering areas along the Pacific coast of Central and South America, where they remain until March or April. While migrating, the Aleutian Tern travels extensively in a series of migratory hops that are usually several hundred miles long.

They travel in loose flocks that can include tens or hundreds of birds, sometimes travel with other tern species. During migration, they are known to rest briefly on offshore islands, beaches, or on the calm ocean surface.

The birds’ navigation is not yet fully understood, but it is thought they use celestial cues, visual landmarks, and Earths magnetic field to navigate. Upon arrival in their wintering area, the Aleutian Tern will find a spot where its food source is abundant, such as shoals or estuaries.

They will typically remain in these areas and feed on small fish and invertebrates throughout the winter. The birds start leaving their wintering areas in late February and early March and undertake the northward migration journey to their breeding grounds.

In the late 20th and early 21st century, the Aleutian Tern’s migratory pattern face new threats through climate change, ocean acidification, and loss of breeding habitat due to increased human activity. Climate change impacts the birds’ food availability at breeding sites, which is often negatively affected by changes in ocean temperature.

Additionally, loss of breeding habitat due to oil spills, development, pollution, and other human activities have caused the bird populations to decline sharply. In Conclusion, the Aleutian Tern is a migratory bird species that experiences two migrations a year from the breeding grounds in Alaska to non-breeding grounds along the Pacific coast of Central and South America.

The bird’s habitats are marine, preferring the coastlines of remote islands where they build their nests. The bird migrates in loose flocks frequently stopping in areas where their prey is abundant.

Climate change, loss of breeding habitat, and increased human activities are some of the critical issues that affect the species, requiring conservation efforts to protect the birds and ensure their continued survival.

Diet and Foraging

The Aleutian Tern is a seabird that feeds on small fish and invertebrates, which it catches by diving into the water from the air. The bird will forage within 12 miles of their breeding colony but may venture farther to feed later in the season.

They prefer small fish like sand lance, herring, and smelt, as well as squid and shrimp.

Feeding

The Aleutian Tern hunts for food in shallow-shore habitats, rocky shores, estuaries, and open water. The bird is known for its unique feeding behavior, which includes fishing by plunge-diving and surface-skimming.

When foraging, the bird can hover over water and scan the area for fish and invertebrates while diving to the surface to catch prey and then flies back up to the sky. These birds are also skilled at locating schools of fish by detecting their underwater shadows.

They will plunge-dive into the water to capture their prey with their sharp beak. They hunt individually and in small groups, and sometimes with other tern species.

Diet

The Aleutian Tern feeds primarily on small fish, typically prey less than 10 cm in length. Some of the fish species that the bird consumes include sand lance, capelin, herring, smelt, and juvenile salmon.

The bird also feeds on invertebrates such as shrimp, squid, and small crustaceans.

Feeding habit varies depending on food availability and breeding season.

Metabolism and Temperature Regulation

The Aleutian Tern has unique physiological mechanisms to survive in their challenging habitats. The bird has a high metabolic rate due to their energy-intensive lifestyle of constant flight, diving, and catching prey.

They have a unique system that helps them maintain their body temperature when migrating in cold water. The bird increases its metabolic rate to produce more heat to maintain its core body temperature.

In addition, during high activity, the bird also breathes more frequently as a way of exchanging heat to increase body temperature, enabling it to tolerate cold temperatures despite their small size.

Sounds and Vocal Behavior

Vocalization

The Aleutian Tern has a variety of calls that it uses for communication between individuals. During the breeding season, the bird produces several calls, including a high-pitched klee-err or kih-luh call.

It is made mainly by males and associates with courtship behavior, and calling is essential in maintaining pair bonds between individuals. Females tend to use a softer call.

They also use sharp, short, and repeated calls when displaying territorial behavior. Outside of the breeding season, the bird produces shorter, more scattered vocalizations used to stay in contact with other members of their flock.

These calls are simpler and less pronounced than the ones made during breeding. The bird also makes a soft purr when soliciting food from their mate or parent.

In conclusion, the Aleutian Tern is a specialized seabird that feeds on small fish and invertebrates, captured by plunge-diving and surface-skimming. The bird has unique adaptations to survive in their challenging habitats, including high metabolism, a unique system to regulate their body temperature in water during migrations.

The tern has distinct vocalizations used for communication between individuals and territories, and calls vary depending on breeding and non-breeding seasons. Understanding the bird’s behavior helps biologists in enacting preservation and conservation strategies to ensure the survival of this beautiful and unique bird species.

Behavior

Locomotion

The Aleutian Tern has a distinctive and elegant flight in the air, making it easy to distinguish from other tern species. They have long, pointed wings that enable them to fly with a graceful, buoyant motion.

When foraging, they can hover over water and scan the area for prey, then quickly dive into the water to capture their prey.

Self-Maintenance

The Aleutian Tern is a relatively independent bird that can fend for itself without much assistance from parents. They possess specialized glands above their eyes that remove excess salt, maintaining electrolyte balance in their body.

The bird keeps its feathers clean, oils them, and preens to keep them waterproof and well-insulated, improving its aerodynamic performance by reducing drag.

Agonistic behavior

The Aleutian Tern, like most terns, is aggressive and will defend their territory from other intruding birds. They will take part in physical confrontations and display aerial chases with other species that get too close to their nesting area.

Sexual Behavior

During the breeding season, the Aleutian Tern will begin courtship behavior. The male bird will display a unique hanging posture that involves bowing its head forward and hanging its wings down, appearing taller, and more attractive.

Males will also offer females prey as part of the courtship process. Females are selective, and male success in courtship depends on his ability to offer food, the size of the fish, and the quality of his territory.

Breeding

The Aleutian Tern breeds in large, dense colonies located on cliff edges, shorelines, and along the coast of islands. The birds return to the same colony and often the same nest site every breeding season.

The pair bond forms during courtship, and both birds will share the task of building their nest using small rocks, seaweed, and other material. The male provides the majority of the material, while the female places it, creating a shallow cavity in which the eggs are laid over the course of several days.

The female bird will typically lay two eggs at a time, which are olive-brown or buff-colored with dark spots and markings. After incubation for approximately 20-22 days, the chicks will begin to hatch.

The chicks are born with a precocial plumage, which allows them to leave the nest within a few days of hatching to search for food with their parents.

Demography and Populations

The Aleutian Tern’s breeding population has been declining since the 1980s due to several factors. The bird is vulnerable to habitat loss, climate change, overfishing, and exposure to pollutants and human activities, such as oil spills and industrial development.

The bird population is estimated at around 12,000 birds, with the majority of the breeding population concentrated in the central Aleutian Islands. Several conservation measures have been put in place to protect the species, including nest box programs, mitigation of oil spills, and monitoring of population size trends.

In Conclusion, the Aleutian Tern performs several behaviors that allow it to survive, mate and maintain itself. The bird is prone to territorial fights during breeding season but is diligent during self-maintenance, like preening and cleaning feathers.

During mating season, males, and females perform actions of courtship. The bird builds its next unique among marine vegetation along the shoreline and clifftops.

The bird fights for survival in the face of environmental challenges and human activities, which have made conservation efforts paramount to the survival of the species. In conclusion, the Aleutian Tern is a migratory bird species that breeds in the remote Aleutian Islands of Alaska and migrates to the west coast

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