Bird O'clock

The Fascinating Life and Plight of the Black-Billed Gull

The Black-billed Gull, also known as the Mackerel gull or Buller’s Gull, is a medium-sized gull species that is native to the southern hemisphere. These gulls are known for their striking black bills and white plumage.

In this article, we will explore the identification of these birds, including their field identification and similar species, as well as their plumages and molts. Identification:

Field Identification:

Black-billed Gulls are about 14-16 inches in length with a wingspan of 38-41 inches.

These birds have a striking black bill that is relatively small and thin, and their eye is surrounded by a white ring. Black-billed Gulls also have bright red legs, which can make them easy to identify.

Similar Species:

As with many bird species, there are some similar-looking gulls that one might encounter while birding. The most similar species to the Black-billed Gull is the Red-billed Gull.

These two species can be challenging to differentiate, especially during the non-breeding season. One notable difference is that the Red-billed Gull has a broader and longer bill than the Black-billed Gull, which is relatively smaller.

Another distinguishing feature is the color of their legs. Red-billed Gulls have a darker, almost black, leg color, whereas Black-billed Gulls have bright red legs.


Black-billed Gulls typically have a distinctive black and white appearance. However, as with most bird species, they go through various plumage changes as they mature.

These plumages are known as molts. Non-breeding Adult:

The non-breeding adults have an all-white head, neck, and underparts.

The back and upper wings are a light grey, and the primary flight feathers are black. The bill is black, and the legs are bright red.

Breeding Adult:

The breeding adults have a black “hood” on their head that extends down to their chest. Their back and wings are still light grey, but their wingtips become more prominent with black spots.

The bill is black, and the legs are bright red. Juvenile:

The juvenile Black-billed Gull has a mottled brownish-grey appearance, with a white belly and wingtips.

They also have a black beak and legs, but their legs are not yet bright red. The head and neck are a mixture of brown and white.


The Black-billed Gull goes through three molts in its lifetime. The first molt occurs when the bird is only six months old, and the second happens during its second year of life.

The third is a complete molt that occurs every year. The complete molt sees the bird replace all of its feathers in one go, ensuring that it can maintain its flight and insulation abilities.

In conclusion, the Black-billed Gull is a distinctive gull species characterized by its striking black bill and red legs. While similar to other gulls in size and shape, the black bill and red legs are easily identifiable features.

Their plumages, including the non-breeding adult, breeding adult, and juvenile, tells a story of the bird’s age and maturity. The molts shed light on how these birds maintain their sleek feathers through the years.

By understanding these characteristics, birders can better identify the Black-billed Gull, enjoy watching them in their natural habitat, and appreciate the beauty of the southern hemisphere’s birdlife. , as the article will wrap up naturally after covering all the necessary information.

Systematics History:

The Black-billed Gull, scientifically known as Chroicocephalus bulleri, is a gull species from the family Laridae. In the past, it was included in the genus Larus, but recent molecular studies have shown that it belongs to a separate genus.

Geographic Variation:

The Black-billed Gull is a medium-sized seagull that is native to coastal parts of New Zealand, southeast Australia, and the Chatham Islands. The species is named after Sir Walter Buller, a 19th-century New Zealand lawyer, naturalist, and ornithologist.


There are two recognized subspecies of the Black-billed Gull:

Chroicocephalus bulleri bulleri – Also known as the New Zealand Black-billed Gull, this subspecies is found across the North and South Islands of New Zealand. Chroicocephalus bulleri darti – Also known as the Australian Black-billed Gull, this subspecies is found in southeast Australia.

Related Species:

The Black-billed Gull belongs to the genus Chroicocephalus, which consists of several small to medium-sized gull species. Some closely related species include the Red-billed Gull, Silver Gull, and White-fronted Tern.

Historical Changes to Distribution:

The Black-billed Gull’s distribution has changed dramatically due to human activity over the past several centuries. In the early 19th century, the species was widespread along the rivers and coastlines of New Zealand and southeastern Australia.

However, by the late 19th century, the population had decreased significantly due to hunting, egg collecting, and habitat destruction. In New Zealand, the population decline was particularly severe.

Black-billed Gulls nested in large colonies along the braided rivers of Canterbury and Otago. The birds were heavily hunted for their feathers, which were used in the fashionable Victorian ladies’ hats.

In addition, the destruction of wetland habitats and the construction of hydroelectric dams, which altered the river flows, further impacted breeding areas. Today, Black-billed Gulls face several ongoing threats, including introduced predators, habitat loss, and disturbances by humans and dogs.

In Australia, the situation is somewhat better for the species. Black-billed Gulls nest along the coasts and estuaries of Victoria, New South Wales, and Tasmania.

Declines in population have been observed, but the species remains relatively common in some areas. Conservation efforts are ongoing, including breeding success monitoring to better understand population trends and habitat management to protect nesting areas.

In conclusion, the Black-billed Gull is a medium-sized seagull that is native to New Zealand, southeast Australia, and the Chatham Islands. The species has faced significant declines in population due to human activity, including hunting, egg collecting, habitat destruction, and the introduction of predators.

Conservation efforts are ongoing to protect Black-billed Gulls, including increased monitoring of breeding success and habitat management. Through these efforts, it is hoped that the species will continue to thrive and provide enjoyment for bird enthusiasts across its range.

, as the article will wrap up naturally after covering all the necessary information. Habitat:

The Black-billed Gull is a coastal species that is mainly found near riverscapes, estuaries, lagoons, coastal cliffs, and sandy beaches.

In New Zealand, breeding colonies are present in braided river systems and other freshwater habitats. The species prefers shallow, slow-flowing water in rivers, where an abundant food source of small fish, insects, and crustaceans can be found.

They are also commonly found in intertidal areas, where they take advantage of marine prey such as shellfish, crabs, and worms. Movements and Migration:

The movements and migrations of Black-billed Gulls vary depending on the population.

In New Zealand, the gulls are generally non-migratory. The breeding colonies of Black-billed Gulls are more dispersed in winter, and they often move downstream into warmer waters.

Despite being resident, the population of Black-billed Gulls in New Zealand is highly mobile, and birds may move several kilometres away from their breeding site to find a reliable food source.

It is fascinating to learn where Black-billed Gulls go during migration.

In contrast to the New Zealand population, the Australian population is known for their migratory patterns. These birds often travel along the southern and eastern coasts of Australia during winter months in search of food.

Many of these birds move to the more favourable feeding areas along Australia’s southern coast and Tasmania, which is where they remain throughout winter. These birds then migrate northward in Australia during spring and summer for breeding, similarly returning south for the winter.

The Black-billed Gull is known for its relatively short-distance migrations, with most birds travelling between 300 and 1500 km. However, some long-range movements are known outside these areas.

A study in New Zealand confirmed the long-range movements of Black-billed Gulls by tracking the birds using GPS monitoring devices. The results showed that the birds migrated up to 2000 km during breeding or post-breeding non-breeding periods, traveling to different parts of New Zealand and Australia.

The migration routes of these birds varied significantly, indicating that individual birds might have unique migration strategies. Migration and movements are significant factors that influence Black-billed Gulls’ conservation efforts and population trends.

The species’ movements and migratory habits suggest that protecting these birds require addressing the areas they migrate through as well as their breeding habitats. Additionally, conservation efforts will need to address the potential mortality sources during the breeding season and migration season.

In summary, the Black-billed Gull has a varied movement and migration pattern depending on the population concerned. While the New Zealand population is non-migratory, the Australian population migrates in search of favourable feeding areas along the southern coast and Tasmania.

The species prefers to stay near slow-moving waters or coastal areas in winter. Being highly mobile, despite being resident, the species expands its breeding territories by looking for reliable food sources and moving several kilometres away from breeding sites.

Black-billed Gulls’ movements not only influence the bird’s conservation but also demonstrate the importance of conservation efforts that encompass the gull’s breeding and migratory grounds. , as the article will wrap up naturally after covering all the necessary information.

Diet and Foraging:


Black-billed Gulls feed primarily on aquatic prey, such as small fish and invertebrates. These birds are opportunistic feeders and have been known to take advantage of any food source that is readily available.

They feed by surface dipping, plunge diving, and foot paddling in the water. Diet:

The diet of Black-billed Gulls varies depending on their location and season.

During the breeding season, the birds prefer to forage in freshwaters such as rivers and lagoons. They feed on a range of small fish and invertebrates, including insects, crustaceans, mollusks, and worms.

During the non-breeding season, they move towards saltwater in search of marine life, including small fish, shellfish, and crabs. Metabolism and Temperature Regulation:

Black-billed Gulls are adapted to their aquatic lifestyle, and their metabolism is adjusted to handle the food they consume’s high water content.

They have a higher metabolic rate than most land birds, allowing them to digest and eliminate excess water from their diet effectively. Additionally, Black-billed Gulls have a high body temperature that helps them maintain their body heat when diving in cold water.

Their thick layer of feathers and oily preen gland on their back provide them with additional insulation, which further enhances their ability to regulate their body temperature. Sounds and Vocal Behavior:


Black-billed Gulls use various vocalisations for communication within their range.

Adults use a range of calls to communicate during breeding and protect their nest and offspring from predators. Young Gulls use different, often higher-pitched calls to communicate with their parents and other Gulls.

Adult Black-billed Gulls have several ‘kree-yah’ calls at their disposal, which they use for communication. The first call signifies a pause in flight or an end of the bird’s feeding activity.

Gulls make this sound when they hover over one place before descending. The second kree-yah call is sharper and harsher, used to communicate with another sitting Gull or for any other communication purposes.

During breeding and nesting prides, the birds become more vocal to communicate. Adult gulls become more agitated during the nesting season when driven by predators or human disturbances.

As a result, they become more vocal and commonly use the distress call ‘argh-argh-argh’ when they feel threatened. When raising their chicks, the Black-billed Gulls use soft chirping sounds to communicate, which are much quieter than their usual calls, to avoid alerting any predators.

In conclusion, Black-billed Gulls are opportunistic feeders that primarily seek out marine prey. Their digestive and metabolic systems are adapted to handle a high water content in their diet, and their body temperature regulation also promotes their ability to dive into cold water.

Black-billed Gulls use different calls to communicate during their breeding season and protect their nests or young from predators. Young Gulls use different sounds from adult gulls to communicate with their parents and other Gulls.

The study of these vocalizations and behaviours provides a unique opportunity for researchers to gain insight into the behaviour and lifestyle of these fascinating birds. , as the article will wrap up naturally after covering all the necessary information.



Black-billed Gulls have a range of locomotion methods that they use depending on their environment and the feeding resources available. When foraging in shallow water, they often hover above the water and then plunge dive from higher above to catch their prey.

They may also use paddling or swimming to move through open water or coastal areas. Self-Maintenance:

Black-billed Gulls have a range of behaviors that are entirely self-maintenance, including preening and stretching.

Preening is the process of cleaning and maintaining their feathers, which are essential for protecting them from the elements and maintaining their buoyancy in the water. Stretching is also important, as it helps the birds to keep their muscles and joints flexible and healthy, both on the ground and in the air.

Agonistic Behavior:

Black-billed Gulls are known for their aggressive and territorial behavior during their breeding season. The birds will defend their nest and offspring aggressively from other Gulls, including with loud vocalizations and physical skirmishes.

Sexual Behavior:

Black-billed Gulls reach sexual maturity at around three years of age. During the breeding season, males compete for receptive females.

Males will perform courtship displays to impress females, which includes displaying the black cap, raising the bill, and fluffing out the feathers. Females will select their mate based on this display.


The breeding season of Black-billed Gulls generally runs from September to February. Breeding pairs will form and defend their breeding territories aggressively.

They will first lay a clutch of two to three eggs, and the chicks will hatch in about three weeks. Both male and female Gulls contribute to the rearing of the chicks, which fledge in about six weeks.

During the breeding season, the gulls are particularly susceptible to human disturbance, predator pressure, and habitat loss. Nests are often exposed to disturbance by beachgoers or motor vehicle drivers and are particularly vulnerable to stoats, rats, and ferrets.

The birds are commonly found nesting in the same area as the New Zealand endangered Black-fronted Terns and Banded Dotterels. Demography and Populations:

The population of Black-billed Gulls has declined significantly over the past 150 years, primarily due to agricultural intensification, habitat loss, predator impact, and hunting.

Predation is a significant threat to breeding populations, especially in New Zealand, where stoats and rats are common predators of the chicks. Currently, the global population of Black-billed Gulls is considered of least concern, with about 85 thousand breedings adults counted across its range.

The Australian subspecies, however, is in decline, with estimates suggesting that there are only about 10 thousand breeding pairs left. Conservation efforts have been put forth to address population trends, including habitat loss, breeding success monitoring, predator control, and public awareness campaigns.

Future research about the demographic trends of Black-billed Gulls is important, especially considering the increasing urbanization of the coastlines of the northern hemisphere, the introduction of new predators, and the pressure of climate change on the birds. As populations experience seasonal changes, it is suggested that they may under greater pressure to feed and to find nesting sites, making ongoing research of paramount importance for the survival of the species.

In conclusion, Black-billed Gulls exhibit a range of behaviors that reflect their aquatic lifestyles in their habitat. They forage through a range of locomotion methods.

During breeding season the birds become aggressive and territorial, but they actively participate in raising their chicks. The population of these birds have faced serious declines over the past century due to anthropogenic factors.

Conservation efforts have been put in place to monitor population trends, habitat loss, predator pressure, and public awareness to secure the survival of these birds. Research outcomes are essential to the preservation of the species, especially in the era of climate change and human encroachment in natural habitats.

In summary, this article has explored various aspects of the Black-billed Gull’s life and nature. We have learned about the bird’s identification, geographical distribution, plumages, and molts.

We have also discussed the bird’s movements and migration patterns, habitat, and feeding habits. Their vocalizations, locomotion, self-maintenance, agonistic behavior, and sexual behavior have been discussed as well.

This article has also looked at their breeding, demography and population trends. The significance of preserving the bird’s habitat and promoting conservation efforts has also been emphasized.

Studying these aspects of the Black-billed G

Popular Posts