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Survival Strategies of the Black-Vented Shearwater: From Prey Diving to Monogamous Pairing

The Black-vented Shearwater, also known as the Puffinus opisthomelas, is a seabird that belongs to the Procellariidae family. These birds are relatively small, and most of their bodies are covered in black feathers.

However, they have a unique feature that makes them stand out from other shearwaters their white underbelly, which can be seen when they are flying over the water. They are mysterious birds, spending most of their time out at sea.

In this article, we will learn more about the identification, plumage, and molts of the Black-vented Shearwater.

Identification

Field Identification

The Black-vented Shearwater is a bird that can be easily identified by its black color and white underbelly. They also have long wings that are narrow and pointed, which help them to stay airborne for long periods.

They have a sharp, hooked bill that is designed to help them catch fish and other prey while flying over the water. Their legs are short and designed for swimming, so the birds are powerful swimmers.

Similar Species

The Black-vented Shearwater is similar to other shearwater species, but it can be differentiated by several features. For example, the Wedge-tailed Shearwater has a longer bill and a different pattern of blackness on their feathers.

The Sooty Shearwater is a much darker bird with a different bill shape, and the Pink-footed Shearwater has pink feet and a different underbelly color.

Plumages

Black-vented Shearwaters only have one plumage, which is black on the upper side and white on the underbelly. They have a white tuft of feathers on their chin, which adds to their unique appearance.

During the breeding season, the birds will become more vocal, calling loudly to one another.

Molts

Black-vented Shearwaters go through a single molt each year before they begin their breeding season. They will lose all of their feathers and grow new ones in their place.

During molt, the birds become flightless, and they will spend much of their time on land. They will rapidly grow new feathers over a period of several weeks, after which they will be ready to take to the skies again and search for food.

In conclusion, the Black-vented Shearwater is a fascinating bird with unique identification features that set them apart from other species. Their plumage is distinct, with black feathers on the upper side and white underbelly feathers.

They go through a single molt each year before their breeding season, and during this time, they will temporarily lose their ability to fly. Although they are elusive and spend much of their time out at sea, the Black-vented Shearwater is a beautiful and interesting bird to appreciate from afar.

The study of the systematic history and geographic variation of the Black-vented Shearwater, a seabird commonly found in the eastern Pacific Ocean, provides valuable insights into the evolution of marine ecosystems. This article will explore the Black-vented Shearwater’s systematics history, geographic variation, subspecies, and related species, as well as historical changes to its distribution.

Systematics History

The Black-vented Shearwater (Puffinus opisthomelas) is a member of the petrel family, Procellariidae, which comprises approximately 100 species of seabirds. The earliest known record of the bird’s discovery was by Juan Ladrillero on his 1557-59 voyage to the Pacific coast of Chile.

The species was first formally identified by French naturalist Philibert Commerson in 1785 based on a specimen collected on his circumnavigation of the globe with Louis Antoine de Bougainville.

Geographic Variation

The geographic variation of the Black-vented Shearwater has been a subject of scientific study for many years. The species is distributed throughout the eastern Pacific Ocean, ranging from the southern part of Alaska to Baja California, Mexico in the north, and from Peru to Chilo Island, Chile in the south.

The species also shows differences in its migratory patterns, with some populations being resident year-round and others being migratory over short or long distances.

Subspecies

The Black-vented Shearwater is further divided into several subspecies, each of which exhibits unique characteristics. The nominotypical subspecies, Puffinus opisthomelas opisthomelas, is found off the coast of Chile.

Puffinus opisthomelas columbinus, which is found off the coast of California, has a different plumage and a smaller bill compared to other subspecies. Puffinus opisthomelas kermadecensis from the Kermadec Islands, and Puffinus opisthomelas opisthoproctus from Mexico, have similar plumage but differ in the size of their bills and wings.

Related Species

The Black-vented Shearwater is closely related to several other species of shearwaters, including the Wedge-tailed Shearwater and the Flesh-footed Shearwater. The Wedge-tailed Shearwater (Ardenna pacifica) is a slightly larger seabird with a more robust bill and darkened underparts.

Flesh-footed Shearwater (Ardenna carneipes) is a larger and darker bird with pink feet and bill. These three species are similar in behavior, diet, and general appearance, with the Black-vented Shearwater exhibiting prominent white belly and black upperparts prominently, compared to the other species.

Historical Changes to Distribution

Historical changes to the distribution of the Black-vented Shearwater have been recorded due to various factors such as climate change, human activity, and the introduction of predators to previously uninhabited islands. For example, fossil records suggest that the species may have once had a much wider range, with evidence of populations in New Zealand and South Africa.

In addition, the decline in seabird populations due to human activity, such as overfishing and oil spills, has also affected the species. Furthermore, the introduction of predators, such as rats and cats, to previously uninhabited islands where the Black-vented Shearwater nests, has resulted in the decline of the species in certain areas.

In Hawaii, for example, the introduction of rats and cats has resulted in the decline and potential local extinction of shorebirds and seabirds, including the Black-vented Shearwater. In conclusion, the study of the systematics history and geographic variation of the Black-vented Shearwater provides valuable insights into its evolution and distribution, as well as the evolution of marine ecosystems.

The species has several subspecies and is closely related to other species of shearwaters. However, historical changes to its distribution, largely due to human activity and the introduction of predators, have affected the species’ population numbers.

Despite this, the Black-vented Shearwater remains an important species to study, in order to better understand the impacts of human activity on marine ecosystems. The Black-vented Shearwater (Puffinus opisthomelas) is a seabird that is generally found in the eastern Pacific Ocean.

This article will focus on the habitat, movements, and migration of the Black-vented Shearwater, including its nesting habits, breeding season and feeding behavior.

Habitat

The Black-vented Shearwater is known for its affinity to the eastern Pacific, where it nests and forages. During the breeding season (March-June), these seabirds find rocky crevices, burrows in cliff tops and small caves to construct their nests up to 3 feet deep.

The species requires no land-cover for nesting since it typically inhabits open rocky or sandy environments near the ocean. Roosting is typically nocturnal and conducted in large groups, which aids in the protection of the birds against predation.

The feeding behaviour however stretches out far beyond the breeding season, where bird travel upwards of more than 2200km to waters rich in food sources.

Movements and Migration

The Black-vented Shearwater is a migratory bird, its movement patterns are largely determined by the availability of food, season and weather. The birds feed on small fish and cephalopods, and during their non-breeding season (June-February), these birds often move northwards to cooler temperate waters in the brackish river mouths to forage.

However, some populations remain close to their breeding sites year-round. The birds are known to make frequent trips between their breeding grounds and seasonal feeding areas, often covering great distances.

It has been recorded that during their non-breeding season, the Black-vented Shearwater migrate as far as British Columbia, Alaska, and the Aleutian Islands. There have also been sightings in Hawaii, with birds moving there in late summer and early fall.

There have been more recent sightings in the Gulf of Alaska extending their feeding areas to the coolest waters of the central North Pacific. The bird bird uses a combination of celestial cues such as the arc of the sun, stars, and the earths magnetic field to navigate.

The shearwaters also follow the currents that flow in the waters where they feed.

Breeding Behaviour

Breeding behavior of the Black-vented Shearwater can vary between locations. For example, colonies in southern California usually mate in late March and early April, while others have been observed breeding during other times of the year.

The birds lay one egg per breeding season, which is incubated by the parents for around 50 days. The chick is then reared by the parents for around three months before it fledges and takes to the sea.

Offspring size varies by subspecies, with the Puffinus opisthomelas opisthomelas having larger chicks that may require up to five months of parental care. The feeding of the young depends on the availability of food, with a predominance of anchovy and sardines being thought to be their preferred diet.

Parents take turns to visit their young at nests and feed them regurgitated fish, which increases in frequency as the chick grows. After fledging, the chicks begin to explore and learn the skills required to survive in open waters.

The young shed their flight feathers soon after they fledge, becoming flightless and remain so for around four weeks.

In conclusion, the Black-vented Shearwater is a migratory seabird that travels great distances during the non-breeding season to access food that its requires.

It breeds along rocky coastlines increasing its need to travel for its main food source. The birds have been observed living in large roosts, providing them with safety in numbers against predators and the use stars, the sun, and the earth’s magnetic field to navigate.

Their breeding behavior is diverse with chicks depending largely on the availability of prey species. As such, more work is required to understand the responses of these birds to rising ocean temperatures and changes in the distribution of prey upon which they rely for survival.

The Black-vented Shearwater (Puffinus opisthomelas) is a seabird that feeds on small fish and cephalopods, which it captures by diving into the ocean. This article will explore the diet and foraging behavior of the Black-vented Shearwater, including its feeding habits, diet, metabolism, temperature regulation, vocalization and calls.

Feeding

The Black-vented Shearwater is a forager and has a unique feeding habit that involves diving into the ocean to capture its prey. The birds use their sharp, hooked beaks to catch small fish and cephalopods such as squid and octopus.

They fly over the waters surface, diving in once they spot their prey with the help of their keen eyesight. The bird twists and turns as it dives, flashing white on their underbelly, where the fish often flock toward, making them easy targets.

The Black-vented Shearwater can catch up to 30 prey items per dive, with feeding time taking up most of the day.

Diet

The Black-vented Shearwater is known for its selective diet, which includes small fish such as anchovies and sardines, crustaceans, and cephalopods. These prey items are typically found in the Eastern Pacific Ocean, where the birds spend most of their time.

The species generally prefers small prey such as myctophids, as they offer a more predictable and stable food source. The birds depend on the presence of these fish and cephalopods, which are usually dormant during the day and rise later at night to feed, allowing the Shearwaters to earn their keep by catching meals where they can.

Metabolism and Temperature Regulation

The Black-vented Shearwaters metabolism and regulation of body temperature have adapted for life in the cold ocean. Research has shown that these birds possess exceptionally large hearts compared to other birds.

This is thought to help with thermoregulation in a cold-water environment, where they need to maintain a body temperature that doesn’t fluctuate rapidly. The large heart is also believed to help them exchange heat with the environment efficiently as they adjust to the ocean’s temperature.

Additionally, the big lungs associated with seabirds allow for increased oxygen capacity and lung ventilation, enabling the bird to more readily supply oxygen to their muscles during busy feeding periods.

Sounds and Vocal Behaviour

The vocalizations of the Black-vented Shearwater are essential for communication between the birds. The birds have a distinctive call that is loud and used during flight to communicate with their mates and chicks, which includes chuckling or hissing sounds, which can carry quite a distance for others of its kind to hear.

Although thought not to be as complex as the vocalization of songbirds, they are still believed to be relatively sophisticated.

Vocalization

The Black-vented Shearwater often reproduces the songs of other species, such as the Cassin’s Auklet and Xantus’s Murrelet, that breed in the close proximity to the Shearwaters. The bird’s breeding calls can also be linked to colony size, where the larger the group, the less discriminative the call.

Conversely, the calls of birds belonging to smaller colonies were more individualistic. In conclusion, the Black-vented Shearwater is a specialized forager with a unique feeding habit that involves diving into the ocean to catch small fish, cephalopods, and crustaceans.

They have a selective diet, which is primarily determined by the availability of prey items that offer a more predictable and stable food source. They have adapted their metabolism to a preferred diet, which can provide ample and consistent fuel for their active, soaring lifestyle.

Their vocalizations are also important for communication and are adapted to the birds’ living environment and breeding conditions. These adaptations are fundamental to a healthy population of Shearwaters, where as they fill important niches in the ocean diet pyramid; their success and survival ensure a healthy marine ecosystem.

The Black-vented Shearwater (Puffinus opisthomelas) displays peculiar behaviors that aid in its successful reproduction. This article will expand on the specific behavior of the Black-vented Shearwater, including its locomotion, maintenance, agonistic and sexual behavior, breeding habits, and population demographics.

Behavior

Locomotion: Black-vented Shearwaters are skilled flyers capable of soaring on thermals and performing aerial acrobatics to capture prey in mid-air. They are known for their straight and swift flight, which is typical of the Procellariidae family.

Their swim pattern is sluggish and used for escaping potential prey on the ground, landing and takeoff. Their well-adapted webbed feet and short legs make them supreme divers, capable of plunging to depths of up to 120 m to capture their prey.

Self-Maintenance: The Black-vented Shearwater engages in a particular behavior called allopreening, which is the preening of feathers by birds on other individuals. Although the purpose of allopreening is still unclear, they appear to use it to cement bonds, alleviate stress, and exchange potential ectoparasites in the colony.

Agonistic

Behavior: Agonistic behavior, exhibited by the Black-vented Shearwater, is an important aspect of territorial defense and food acquisition. The birds perform aerial chases, dive bombing, beak jabbing and fighting when competing with their peers for resources.

Sexual

Behavior: Black-vented Shearwaters engage in complex courtship rituals during the breeding season. These displays include bill clacking, head swaying, and wing flapping.

These courting behaviors are also used for pair formation and reaffirmation.

Breeding

Breeding occurs between March and June during the thermally stable upwelling season, where birds form monogamous pairs for the breeding season. Unlike other seabirds that build nests on the ground or cliffs, Shearwaters lay their single egg in burrows excavated in soil or in crevices among rocky cliffs.

The chicks are fed regurgitated fish by both parents for around 90 days before they fledge and leave the nest. Parents often fly long distances to forage to have enough food for their single chick.

Demography and Populations

The Black-vented Shearwater has a large breeding range, which spans both North and South America. However, the population of Black-vented Shearwaters has been declining due to a number of factors, including habitat loss, overfishing, bycatch in fishing nets, and the introduction of rats and other predators to nesting islands.

These factors have resulted in declines across the range of the Black-vented Shearwater, with many subpopulations now of concern due to local population declines. The International Union for Conservation of Nature and Natural Resources have listed the species as Near Threat

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