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Soaring Above the Pacific: Discovering the Wonders of Buller’s Shearwater

Buller’s Shearwater: The Pacific Ocean’s Master GliderWhen it comes to seabirds’ breathtaking displays of aerial prowess, few species compare to the Buller’s Shearwater. This magnificent bird can be found darting gracefully across the ocean’s surface, its wings and tail perfectly choreographed in an intricate dance as it seeks out its next meal.

However, the Buller’s Shearwater is not only a wonder to watch in flight but also in terms of its distinct physical features and unique lifecycle. Read on to learn more about this remarkable bird’s identification, plumages, and molts.

Identification

Field Identification

For novice birdwatchers, identifying Buller’s Shearwaters can be a daunting task since they resemble many other shearwater species. However, there are a few key characteristics to look out for, both in flight and perched.

In general, the Buller’s Shearwater has a medium-sized, robust build, with a wingspan of approximately 3 feet. It also boasts an elongated head and slender neck, which add to its aerodynamic capabilities.

Its wings have a distinct silhouette, with a slightly hooked tip and pointed inner primaries. The bird’s underparts are white, and its upperparts are a dark brownish-grey, which creates a striking contrast when seen in flight.

Similar Species

Several other shearwater species share some similarities with Buller’s Shearwaters, such as the Sooty Shearwater and Pink-footed Shearwater. However, the former has a longer wingspan, while the latter has a shorter bill.

The Short-tailed Shearwater is also unique, with its distinctive call and more prominent brow ridges.

Plumages

Like many other seabird species, Buller’s Shearwaters undergo several plumage changes over their lifetime. Juvenile Buller’s Shearwaters have dark brown feathers on their upper parts, heavily marked with pale-edged, buff-tipped feathers.

Their belly and throat are white, while their flanks are heavily barred with dark brown. The bird’s head is an ashy-gray, with a thin, dark bill and dark eyes.

Adult Buller’s Shearwaters undergo three different plumage cycles: basic, alternate, and breeding. In their basic phase, the bird’s underbody is a pristine white, and their back and wings are all dark brown.

Their beak is horn-colored, which is why they are sometimes called the Horn-colored Shearwater. During the alternate phase, the bird’s feathers on their upperparts have a reddish-brown hue mixed with dark and light gray.

When breeding, adults have a distinct purple or pink wash on their abdomen, and the rest of their underbody becomes grayer and speckled with black flecks.

Molts

Buller’s Shearwaters undergo a different molting process than most birds. They have an alternate plumage cycle, which occurs once a year in late summer to early autumn.

During this time, many of their flight feathers are shed and replaced, resulting in a brown-plumaged transformation. The adult’s primary feathers are replaced over an extended period, which allows for uninterrupted flight and foraging as they wait for new growth.

Conclusion

Buller’s Shearwaters are truly remarkable birds with striking features, unique life cycles, and impressive flight capabilities. Surely, these magnificent seabirds have acquired noteworthy characteristics, allowing them to thrive in the harsh and dynamic Pacific Ocean environment.

Studying these birds’ habits and behaviors could greatly benefit marine conservation efforts in the future, making information about them invaluable. Whether you’re a seasoned birder or just starting, you can’t go wrong, as these birds are sure to provide a fascinating sight for all to see.

Systematics History

The Buller’s Shearwater, also known as Ardenna bulleri, is part of the seabird family Procellariidae, which contains over 90 species of petrels and shearwaters. The species was first described in 1881 by Captain Henry Buller, a British ornithologist, after whom the bird was named.

Geographic Variation

Buller’s Shearwaters inhabit a vast range of oceanic habitats across the southern hemisphere, including the waters around New Zealand, Australia, and Chile. However, variations in their physical characteristics and vocalizations have been observed between populations in different geographic locations.

Subspecies

There are currently three recognized subspecies of Buller’s Shearwaters: Ardenna bulleri bulleri, Ardenna bulleri platei, and Ardenna bulleri parkinsoni. The first subspecies is found exclusively in New Zealand, while the second and third are found in Chile and Australia, respectively.

Ardenna bulleri bulleri has an elongated head and a moderately robust body shape, with a wingspan of 78-82 cm. The bird displays a dark-grey-brown upper body, with a pale belly and white underwings and under tail covert feathers.

On the other hand, the Ardenna bulleri platei, which is found off the coast of Chile, has a slightly paler appearance, with a lighter grayish-brown upper body and more contrasting white underwings. The Ardenna bulleri parkinsoni, which inhabits the Tasman Sea between Australia and New Zealand, is typically smaller in size than the other subspecies, with a wingspan of 70-75 cm.

Its plumage is a darker gray-brown color with a more distinctly marked white underbelly compared to the other two subspecies.

Related Species

Buller’s Shearwater is closely related to other shearwater species, including the Wedge-tailed Shearwater and Sooty Shearwater. Genetic studies have shown that these species have a common ancestor and are part of the same evolutionary lineage.

In fact, many researchers have suggested that Ardenna bulleri is part of a superspecies made up of several related species.

Historical Changes to Distribution

Buller’s Shearwater’s range and distribution have undergone significant changes over the last two centuries. Historical records show that the species’ range was once limited to the waters surrounding New Zealand, where it breeds in large numbers on offshore islands.

However, since the early 1900s, the species has expanded its range to include other regions of the southern hemisphere. One of the most significant changes was the establishment of a breeding population of Buller’s Shearwaters on Lord Howe Island, an Australian territory located about 600 kilometers east of the Australian mainland.

Colonization of the island occurred sometime in the mid-20th century, and the species has since established a permanent breeding population there. The reason for the species’ expansion into this new range is unclear, although it is suggested that it may be due to changing oceanic conditions or an increase in the availability of food resources in the region.

Another significant change in distribution has been observed in the species’ breeding habitats. Buller’s Shearwaters, like many other seabird species, have experienced habitat loss due to human activities such as deforestation and introduced predators.

In particular, many of the species’ offshore breeding islands have been disturbed by introduced species such as rats, cats, and pigs, which have caused significant damage to the native vegetation and precipitous declines in the breeding populations. In response, conservation organizations have implemented measures to control invasive species’ populations and restore breeding habitats.

As a result, Buller’s Shearwater populations have rebounded on some breeding islands, although the species’ overall population trend remains uncertain.

Conclusion

Buller’s Shearwater is a remarkable seabird whose distribution, plumage, and vocalizations have evolved to suit the extreme and dynamic southern hemisphere oceanic environments. Despite the species’ successful expansion into new ranges, it faces significant threats from habitat loss, predation, and human disturbance.

Research into the species’ systematics and historical changes in distribution is crucial for designing effective conservation strategies to protect these remarkable birds.

Habitat

Buller’s Shearwater is primarily found in oceanic habitats and offshore islands throughout the southern hemisphere. During the breeding season, adults will return to the same breeding sites year after year, which are typically small, remote offshore islands.

These islands provide suitable habitats for the birds to nest, which can include rocky crevices, burrows, or shallow pits. Buller’s Shearwaters will spend long periods at sea outside of the breeding season, returning only to the breeding sites to mate and nest.

During this time, they are often found in pelagic waters close to their breeding grounds, such as upwellings, where they can find abundant food resources.

Movements and Migration

Buller’s Shearwaters are known for their long-distance foraging trips, often traveling hundreds of kilometers in search of food. They have been observed traveling up to 800 km from breeding colonies to forage.

In addition, the birds have also been observed traveling thousands of kilometers across the southern hemisphere for non-breeding activities. One of the most notable movements observed in Buller’s Shearwaters is a trans-equatorial migratory route from New Zealand to the North Pacific.

During the breeding season, birds from New Zealand are known to disperse northward, traveling across the equator and into the tropical waters of the Pacific Ocean. Here, they will remain for several months, regularly foraging and resting before returning to their breeding sites.

Studies suggest that the movement patterns and migration routes of Buller’s Shearwaters are largely influenced by changing oceanic conditions, such as the locations of food resources and favorable winds. As such, the species’ movements and migration patterns can vary significantly year to year.

In recent years, scientists have been using satellite tracking technology to better understand the movements and migration patterns of Buller’s Shearwaters. These devices have allowed researchers to track their movements in real-time, providing valuable insights into the species’ behavior and ecology.

Conservation Implications

While Buller’s Shearwaters are known for their remarkable movements and migrations, this behavior also makes them vulnerable to a range of threats, including oceanic pollution, climate change, fishing pressure, and incidental bycatch in commercial fisheries. Their reliance on oceanic habitats, including pelagic waters close to their breeding sites, makes them particularly vulnerable to changes in oceanic conditions, such as changing water temperatures and sea level rise.

In addition, invasive species such as rats, cats, and pigs have caused significant damage to Buller’s Shearwater breeding habitats, causing declines in the species’ breeding populations in some areas. To protect Buller’s Shearwaters, a range of management strategies have been implemented, including the control of invasive species on breeding islands, the identification and protection of important foraging areas, and the reduction of bycatch in commercial fisheries.

Conclusion

Buller’s Shearwaters are remarkable seabirds with unique movement patterns and migration routes. Their reliance on offshore habitats, travel over long distances, and susceptibility to a range of threats underline how crucial it is to conduct more research and management strategies to protect these birds.

Exploring more innovative ways of understanding their ecological and behavioral patterns could also support the development of strategies that will guide how we manage and protect our oceans, safeguarding and conserving the well-being of these important species.

Diet and Foraging

Feeding

Buller’s Shearwaters are well known for their remarkable movements and migration patterns in search of food. They feed primarily on small fish, squid, and krill.

They forage by diving into the water and using their wings to swim after prey, using their sharp bill to capture food. Buller’s Shearwaters are also known to follow marine mammals, such as dolphins, as they feed on schools of fish, taking advantage of the animals’ disturbance of fish to capture prey for themselves.

The birds have also been observed following fishing boats, feeding on discarded catch and offal.

Diet

Studies have shown that the diet of Buller’s Shearwaters varies depending on the time of year and the location of foraging grounds. During the breeding season, the birds will typically feed on moderately small fish species and planktonic krill, which are abundant in the waters around their breeding colonies.

In contrast, during the non-breeding season, the birds are known to travel long distances to forage in regions with abundant squid populations, which can include the Southern Ocean and parts of the South Pacific.

Metabolism and Temperature Regulation

Buller’s Shearwaters are endothermic animals, which means they have the ability to generate and maintain their body heat. To maintain their body temperature, the birds have a high metabolic rate, which requires them to consume large amounts of energy-dense food.

To support their high metabolic rate, Buller’s Shearwaters have several adaptations that allow them to conserve heat and regulate their body temperature. These adaptations include a thick layer of feathers to insulate the body, a countercurrent heat exchange system in their legs to maintain core temperature, and a compact body that minimizes heat loss.

Sounds and Vocal Behavior

Vocalization

Buller’s Shearwaters are highly vocal birds, with a variety of calls and vocalizations. Their vocalizations play an essential role in communication during breeding and foraging activities, as well as in navigating in low light conditions.

During the breeding season, males and females engage in mutual preening, which is accompanied by a complex series of vocalizations. These calls are thought to play an essential role in pair bonding and courtship rituals.

Buller’s Shearwaters also use their vocalizations to locate and communicate with each other during foraging activities. For example, the birds will often call out to each other during feeding to stay in contact and indicate the location of prey.

One notable call made by Buller’s Shearwaters is the “kuk” call, which is used during flights over water and is accompanied by a series of short whistles. These calls are typically made by individuals flying low over the water, and are thought to serve as a contact call between birds in a group.

Conclusion

Buller’s Shearwaters are remarkable seabirds with unique ecological and behavioral characteristics that enable them to thrive in the harsh and highly dynamic oceanic environments of the southern hemisphere. Their endothermic nature, vocalization, and foraging behavior enable them to survive and adapt to the different seasons and oceanic conditions.

Further research and monitoring of their biological and behavioral patterns are essential for protection and conservation strategies to ensure that their delicate way of life is sustained for future generations.

Behavior

Locomotion

Buller’s Shearwaters have highly specialized wings and can glide for long periods without flapping, allowing them to soar above the ocean’s surface for extended periods. They are also skilled swimmers, using their wings to “fly” underwater and catch prey.

The bird’s streamlined body, long wings, and aerodynamic shape make them well-adapted for both aerial and aquatic locomotion.

Self Maintenance

As with many seabirds, preening plays a crucial role in maintaining the Buller’s Shearwater’s feathers and waterproofing. Birds will use their beaks to clean and arrange feathers, removing dirt, and oil and redistributing it to neighboring feathers.

Agonistic Behavior

Like many seabirds, Buller’s Shearwaters can be highly territorial during the breeding season, with pairs aggressively protecting their nesting sites from intruders. Territorial disputes can lead to aggressive vocalizations, physical conflict, and, in some instances, mortality.

Sexual Behavior

Buller’s Shearwaters are monogamous birds, with individuals often returning to the same breeding colony and mate year after year. During courtship, males and females perform duets, calling to each other while standing close and bobbing their heads.

Successful romantic partnerships are shown to depend on the quality of the nest site and the male’s song quality.

Breeding

Buller’s Shearwaters breed during the austral summer along offshore islands and on the mainland coasts of New Zealand, Chile, and Australia. During the breeding season, pairs of birds will return to the same breeding site year after year, utilizing the same nest burrow or crevice for their eggs and chicks.

After pair formation in late November, they begin nest site selection, which includes digging a burrow to lay the egg and defend the site from intruders. The species lays a single white egg that is incubated for approximately 50 days by both parents before hatching.

Both parents are involved in the chick-rearing process, with the male providing food for the female, who remains with the chick, and the female and chick switching roles once the chick gets older. Chicks fledge approximately 80-90 days after hatching, and parents will continue to feed and care for them even after fledging, sometimes for several weeks.

Demography and Populations

The global population of Buller’s Shearwaters is currently estimated to be between 4 and 6 million individuals, with the majority of the population inhabiting the waters around New Zealand. In recent decades, the species’ population has experienced significant population declines in some areas, mostly due to introduced predators and habitat destruction caused by human activities.

The conservation status of the Buller’s Shearwater varies greatly throughout its range, with populations in some regions considered to be declining or at risk of decline. Conservation measures, including the eradication of invasive species on breeding islands and the education of the general public, have largely been successful at enabling population recovery and contributing to the species’ protection.

However, more research and conservation efforts are necessary to continue protecting and preserving these magnificent seabirds for future generations.

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