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8 Fascinating Facts About the Black-Tailed Gull

Bird: Black-tailed Gull, Larus crassirostrisThe black-tailed gull, also known as Larus crassirostris, is a seabird that is native to East Asia, breeding along the coasts of China, Japan, and Korea. These gulls are medium-sized and can be distinguished by their yellow beaks and black tail feathers, giving them a unique and striking appearance.

In this article, we will explore everything you need to know about these magnificent birds, from their identification to different plumages and molts. Identification:

Field Identification:

The black-tailed gull is a medium-sized bird with a length of around 47-52cm, and a wingspan of around 125-140 cm.

They have a white body and dark wings with black primary feathers. A distinguishing feature of this gull is their yellow bill and black tail feathers.

These birds also have pink legs and a white head and neck, with dark patches around their eyes. These patches help to distinguish it from other gull species.

Similar Species:

It is important to note that the black-tailed gull can be easily confused with other gull species such as the herring gull and the lesser black-backed gull. However, the black-tailed gull is much smaller in size, and lacks the pink legs and dark patches around the eyes that are present in these other gulls.

Plumages:

Gulls, like many other bird species, have different plumages throughout their life cycle. The black-tailed gull also follows this pattern with various plumages that can help distinguish them based on their age.

Adults of this species have a white body, dark mantle and wings, yellow bill, and pink legs. The tail feather is black, and the bird’s eyes are dotted with a thin and blue eye shadow.

In juveniles, the wings and mantle are brownish-grey, and the bill is pink with a black tip. The eyes are brown.

As the bird ages, it gradually loses its brownish-gray plumage to obtain adult plumage. The feathers on the body do not have much change from year to year.

Molts:

Gulls’ feathers undergo various molt patterns throughout their lives. These molts can also help determine the gull’s age.

Black-tailed gulls have two molts each year, one in the spring and one in the fall. They spend much of their life cycle in winter and only a couple of months breeding in the summer.

The molting process occurs from head to tail feathers, with adult birds taking longer to molt than immature birds. The immature birds take approximately three years to molt completely, while adults take four or more years to complete the process.

Conclusion:

In conclusion, the black-tailed gull is a fascinating bird species, with a striking appearance and distinct plumages based on their age. They are found along the coasts of East Asia and can be easily identified by their yellow beaks and black tail feathers.

The molting process can also be used to determine the gull’s age and maturity. Understanding the identification, plumages, and molting patterns of the black-tailed gull is essential for any bird enthusiast, and this article has provided a comprehensive overview of this bird’s life cycle.

Systematics History:

The systematics of the black-tailed gull, Larus crassirostris, has undergone significant changes over the years, as scientists have gained more knowledge of the bird’s genetic makeup and morphology. The bird’s classification has been the subject of many debates, with scientists initially classifying them as a subspecies of the herring gull.

However, later studies revealed that the black-tailed gull was distinct from the herring gull and closer in relation to the glaucous-winged gull. Geographic Variation:

Black-tailed gulls have a wide range, with populations found throughout East Asia, breeding in China, Japan, Korea, and the Russian Federation.

Their range extends to the Yellow Sea, northern Sea of Japan, and southern Kamchatka Peninsula, with some sightings reported in Alaska and Hawaii. Subspecies:

The black-tailed gull has several subspecies, with varying ranges in China, Japan, and Korea.

Some of the subspecies include:

– Larus crassirostris crassirostris: This subspecies is found in Japan, breeding in areas such as Izu Islands and Bonin Islands. – Larus crassirostris heinei: This subspecies occupies a range in China and breeds on Zhongjian Island, near the mouth of the Yangtze River.

– Larus crassirostris kamtschatschensis: This subspecies is found in eastern Russia, on the Kamchatka Peninsula, and breed in colonies around the Sea of Okhotsk. Related Species:

The black-tailed gull belongs to the gull family, Laridae.

This family includes more than 100 species, including the herring gull, black-headed gull, and glaucous gull. The black-tailed gull’s closest relative is the glaucous-winged gull, and both species have been known to interbreed in regions where their ranges overlap.

Historical Changes to Distribution:

The range of the black-tailed gull has undergone significant changes over time. The bird’s range was initially limited to Japan, but they have since expanded their range to include areas in China and Korea.

There have also been reports of black-tailed gulls outside their traditional range, with sightings in Alaska and Hawaii, indicating a possible expansion of their range. The reasons for this expansion are not entirely clear, but it could be due to changes in temperature patterns, habitat availability, or migration patterns.

The bird’s breeding range has also shifted over time, with some colonies expanding their distribution, while others have declined. The construction of harbors and other coastal development activities have impacted their breeding sites, leading to a decline in numbers.

The black-tailed gull has also been subject to hunting for food in some areas. In Japan, they were considered a delicacy, leading to overhunting and a significant decline in their population.

However, hunting has since been regulated, and the population has stabilized. Conclusion:

The black-tailed gull is a fascinating bird species with a rich systematics history.

The variations in their range, subspecies, and relation to other bird species have been the subject of much research. The bird’s range has undergone significant changes over time, expanding to include areas in China and Korea, and sightings have been reported outside their traditional range in Hawaii and Alaska.

Human activities such as habitat destruction and hunting have also impacted their population. Understanding the black-tailed gull’s distribution and history is critical in developing conservation strategies that ensure their survival.

Habitat:

The black-tailed gull occupies a range of habitats, breeding on islands and coastal areas. Their preferred habitat includes rocky cliffs, sandy beaches, and open grassy areas.

They also prefer areas close to fishing grounds, enabling them to scavenge for food. The birds are known to breed on offshore islands and rocky outcrops, where they are relatively safe from predation by terrestrial predators, including humans.

During the non-breeding season, black-tailed gulls can be found in a range of habitats, including coastal waters, estuaries, and rivers. They are known to feed on crustaceans, fish, and other marine invertebrates in shallow waters.

The gulls are also known to roost on offshore rocky reefs or sandy beaches. Movements and Migration:

Black-tailed gulls are generally non-migratory, but their movements are influenced by the availability of food sources.

During the non-breeding season, they may move away from islands to forage for food in new areas. Juvenile birds may also disperse to unfamiliar territories, leading to sightings outside their breeding range.

Some black-tailed gulls have been known to undertake short migrations, moving between regions to take advantage of seasonal food sources. For example, some birds have been observed moving to the coast of Japan during the winter months.

During the breeding season, black-tailed gulls remain close to their breeding grounds, limiting their movements significantly. However, the birds may fly out to sea to forage for food and then return to their nests.

The maximum distance recorded for a black-tailed gull during a foraging trip was 168 km offshore. In addition to their movements, black-tailed gulls also exhibit flocking behaviors.

During non-breeding periods, they may form large flocks of up to a thousand birds. These flocks are also known to mix with other gull species, especially during periods of food scarcity or roosting.

Breeding black-tailed gulls exhibit territorial behavior, with each pair defending its assigned breeding site against intruders. The birds may also become aggressive when their chicks are threatened or disturbed, sometimes flying up to 100 meters away from the nest to attack intruders.

Conclusion:

Black-tailed gulls occupy a range of habitats, including coastal areas, grassy fields, and offshore islands, mostly breeding on rocky cliffs and islands close to fishing grounds. The birds are non-migratory but may move away from their breeding grounds to forage for food during the non-breeding season.

They also exhibit flocking and territorial behavior, with breeding pairs defending their nests against intruders. Understanding the movements and behavior of black-tailed gulls is vital in developing conservation strategies to protect these birds’ populations.

Diet and Foraging:

Feeding:

Black-tailed gulls are opportunistic feeders, scavenging for food in a range of environments and habitats. They are omnivores and feed on a variety of prey, including fish, crustaceans, mollusks, insects, and small mammals.

During the breeding season, the birds often feed on fish, squid, and krill, which are abundantly available in the coastal waters close to their breeding areas. When foraging for food, black-tailed gulls fly over shallow waters, scanning the surface for fish or other prey.

They use their keen eyesight to locate prey, and once they spot something, they dive headfirst into the water, using their wings to swim through the water after their prey. Diet:

Black-tailed gulls’ diet varies depending on the season and availability of prey.

During the breeding season, they feed mainly on small fish, squid, and krill, but may also eat insects, crustaceans, and other marine invertebrates. In the non-breeding season, the gulls may feed on a wide variety of foods, including fish, crabs, mussels, and other invertebrates.

They may also scavenge for food in urban areas, including scraps from garbage containers, which can lead to conflicts with humans. Metabolism and Temperature Regulation:

Black-tailed gulls are adapted to the marine environment and are capable of regulating their body temperature in cold water.

They have a high metabolic rate, allowing them to withstand the cold temperatures of their environment. The birds also have a specialized gland above their eyes that helps regulate salt levels, allowing them to drink seawater without becoming dehydrated.

This adaptation enables them to survive in environments with limited freshwater. Sounds and Vocal Behavior:

Vocalization:

Black-tailed gulls are highly vocal and use a range of calls to communicate with other birds.

They have a variety of calls, including alarm calls, territorial calls, and courtship calls. Their calls vary in intensity, pitch, and duration, and are accompanied by a range of body movements and postures.

During the breeding season, black-tailed gulls use a loud “ah-eeh” call to establish and defend territories. They also use a low “krug” call to warn off intruders or predators.

Non-breeding birds may use a range of calls, including a high-pitched “quee-quee” sound when foraging for food or flying over water. The chicks of black-tailed gulls also use a range of vocalizations to communicate with their parents.

They use a “begging call” to signal when they are hungry, and the parents respond by regurgitating food into their beaks. Conclusion:

Black-tailed gulls are opportunistic feeders, scavenging on a wide range of prey, including fish, crustaceans, and marine invertebrates.

They are adapted to their marine environment, regulating their body temperature and salt levels to survive in cold coastal waters. The birds are highly vocal, using a range of calls to communicate with each other, including territorial calls, alarm calls, and courtship calls.

Understanding the diet, foraging behavior, metabolism, and vocal behavior of black-tailed gulls is vital in developing conservation strategies to protect these birds’ populations. Behavior:

Locomotion:

Black-tailed gulls are highly adaptive birds, capable of moving both in the air and in the water.

They are strong fliers with excellent vision, which enables them to locate their prey from a great distance. When in water, black-tailed gulls use their wings to swim and hunt prey such as fish, mollusks, and crustaceans.

Black-tailed gulls also use their wings to catch the wind while gliding over water or land. Self-Maintenance:

Black-tailed gulls are known for their fastidious nature and spend a considerable amount of time grooming themselves.

Grooming involves preening their feathers and removing dirt and parasites from their feathers and skin. They keep their feathers clean and in good condition by applying waterproofing oil from a gland near the base of their tails.

Agonistic Behavior:

Black-tailed gulls, especially during breeding season, exhibit agonistic behavior. Agonistic behavior includes threatening, attacking, or avoiding other birds of their same species or predators or intruders.

Black-tailed gulls do this to establish and defend their territory, breeding areas and their mates. Sexual Behavior:

Black-tailed gulls develop pair bonds and mate for life.

Courtship behavior starts by the male choosing and presenting the female with food and calling out to her. After they form bonds, the pair will preen each other’s feathers, copulate, and build a nest where they will breed.

They will also share the responsibility of incubating their eggs and feeding their young.

Breeding:

Black-tailed gulls breed in colonies, where they compete for territories and mates.

Breeding typically occurs from April to May, when the birds construct nests on rocky ledges or the ground. The female will lay one to two eggs, which both parents will incubate for about 25 to 28 days.

Once the eggs hatch, the parents will feed the chicks for about eight weeks before they fledge and become independent. The breeding success of black-tailed gulls is highly dependent on their access to nesting sites and food availability.

The construction of coastal developments such as harbors and marinas can threaten nesting sites, leading to a decline in the population and breeding success rates. Demography and Populations:

The population of black-tailed gulls appears to be stable, with an estimated global population of around 200,000 individuals.

The birds’ range in East Asia extends over 22 degrees of latitude and has a diverse population distributed in Japan, China, Korea, and the Russian Federation. However, some studies suggest that the breeding success of black-tailed gulls is declining in some areas due to habitat loss.

Changes in the availability of food sources, climate change, and hunting for food or for their feathers have also impacted the gulls’ population and breeding success. Conclusion:

Black-tailed gulls exhibit a range of behavior, including fastidious self-maintenance, and agonistic behavior during the breeding season.

Their sexual behavior involves pair bonding, courtship, and shared parenting of their young. The birds’ breeding is affected by habitat loss and declining availability of food sources.

Understanding the behavior, breeding cycle, and population trends of black-tailed gulls is essential in developing conservation strategies that will conserve their populations in the future. In conclusion, the black-tailed gull is a fascinating bird species that has undergone significant changes to its systematics, range, and behavior.

Understanding the bird’s identification, plumages, molting patterns, habitat, movements, foraging, behavior, breeding cycle, and demographics is critical in developing effective conservation strategies to protect their populations. The black-tailed gull is an important indicator species that can help us understand the health of coastal ecosystems.

We need to identify the threats such as habitat loss, climate change, and hunting, which impact their populations and develop effective measures to conserve these birds. The future of the black-tailed gull relies on our ability to protect and preserve the coastal ecosystems where they live.

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