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Discover the Fascinating World of Stewart Island Shags: Behaviors Plumages and Populations

Birdwatching is a popular hobby, and for good reason. Birds are fascinating creatures that come in all shapes and sizes, each with its own unique characteristics.

In this article, we will focus on one specific bird species, the Stewart Island Shag, also known as Leucocarbo chalconotus. We will cover various topics such as identification, plumages, molts, and more, to help you get to know this bird better.

Identification

The Stewart Island Shag is a medium-sized bird that can grow up to 70 cm long and weigh around 1 kg. It has a long, thin neck, and a sharp, pointed beak, which it uses to catch fish in the water.

The adults have a black head and a white patch on their neck, while their upper body and wings are black with a greenish tinge. The underpart of their body is white.

Juvenile birds have brown upperparts and white underparts. They also have a white spot on their forehead.

Field

Identification

One way to identify the Stewart Island Shag is by its distinct call, which is a series of croaks and screeches. It is also a coastal bird, often spotted near rocky shores and inlets.

When flying, it has a distinct and direct flight pattern.

Similar Species

The Stewart Island Shag is often confused with other shag species such as the Otago Shag, which has a smaller size, a shorter neck, and no white patch on its neck. Similarly, the Spotted Shag has white spots on its back, wings, and head, and a larger white patch on its neck.

Plumages

The Stewart Island Shag has distinct plumages that change throughout its life. It has three main plumage types: juvenile, breeding, and non-breeding.

Juvenile: The juvenile plumage is brown on the upper body and white on the underparts. They still have their white forehead spots.

Breeding: The breeding plumage is black on the head and upperparts, with a white neck patch. The underparts are white.

Non-breeding: The non-breeding plumage is similar to the breeding plumage, but the black feathers have a greenish tinge.

Molts

Molts are an essential part of a bird’s life as they help renew their feathers, which is vital for their survival.

The Stewart Island Shag has two molts: Prebasic and Prealternate.

– Prebasic: The Prebasic molt happens once a year, typically in the late summer/early fall. During this molt, the bird replaces its feathers on the body, wing, and tail.

– Prealternate: The Prealternate molt happens in the spring. During this molt, the bird replaces the feathers on its head and neck.

In conclusion, the Stewart Island Shag is a unique bird species that is fascinating to observe, with its nests perched atop rocky ledges and its sharp beak and distinctive call. With an understanding of its identification, plumages, and molts, you can better appreciate this species on your next bird-watching expedition.

Systematics History

The Stewart Island Shag’s scientific name is Leucocarbo chalconotus, which belongs to the order Suliformes and the family Phalacrocoracidae. This family consists of around 40 species of cormorants and shags found in coastal and freshwater habitats across the globe.

The taxonomy of the family has undergone numerous revisions and is still the subject of much debate.

Geographic Variation

The Stewart Island Shag is found on the southernmost coast of New Zealand, primarily on Stewart Island and the smaller islands surrounding it. These birds have a limited distribution, with few specimens being seen anywhere else in the world.

Consequently, little is known about their geographic variations, behaviors, and habits.

Subspecies

There are four subspecies of the Stewart Island Shag, which vary in size, plumage, and distribution. – L.

c. chalconotus: This subspecies is found on Stewart Island and its surrounding islands.

It is the largest and darkest of the four subspecies, with greener plumage on its back. – L.

c. purpurascens: This subspecies is found on the Snares Islands, approximately 100 km northwest of Stewart Island.

It is smaller than the L. c.

chalconotus and has a purple sheen in its plumage. – L.

c. stictocephalus: This subspecies is found in the Chatham Islands, approximately 900 km northeast of Stewart Island.

It has a smaller bill than the other subspecies and is lighter in color. – L.

c. undulatus: This subspecies is found on the Antipodes Islands, approximately 760 km southeast of Stewart Island.

It has a smaller bill and a more wavy or undulating plumage pattern.

Related Species

The Stewart Island Shag is closely related to other cormorant and shag species found across New Zealand and Australia. These birds belong to the Leucocarbo genus, which includes over 20 species of shags and cormorants.

Historical Changes to Distribution

The Stewart Island Shag’s distribution has largely remained unchanged, given that it has always been restricted to the coast of Stewart Island and its surrounding islets, with occasional sightings on the coasts of South Island and Fiordland in Southwestern New Zealand. However, it is believed that the population of this species has decreased, in particular, the subspecies purpurascens, as a result of habitat loss and predation by introduced mammals.

It is believed that the decline in the population of the Stewart Island Shag has been linked to the decline of kelp beds in New Zealand’s coastal waters. Kelp beds are an essential habitat for the species as they are used by the birds for roosting, nesting, and foraging.

The decline of these kelp beds has been attributed to a combination of factors such as environmental changes, pollution, and overfishing. Another significant threat to the Stewart Island Shag’s population is introduced mammals, such as rats, stoats, and cats, which prey on the birds and their eggs.

These invasive species have affected populations of several native bird species in New Zealand, including the Stewart Island Shag.

Conclusion

The Stewart Island Shag is a unique bird species that plays an important ecological role in New Zealand’s coastal ecosystems. With their unique plumage, behaviors, and habitats, these birds are fascinating to observe.

Although their geographic variation and distribution are limited, their subspecies adaptation to their specific environments is a testament to the resilience of nature. As with many other native bird species in New Zealand, the Stewart Island Shag’s population is under threat from habitat loss and invasive species, highlighting the need for conservation measures to protect this bird species for future generations.

Habitat

The Stewart Island Shag is a coastal bird that is found in the southern regions of New Zealand. These birds have adapted to a range of coastal habitats, including rocky shores, cliffs, and shallow inlets with kelp beds.

They are rarely seen far from the shoreline, as they prefer to forage and nest near the water’s edge. One unique habitat of the species is the Stewart Island Marine Reserve, which is located around the island’s southern coast.

The reserve is home to a range of marine species, including the Stewart Island Shag. The reserve’s kelp forests provide the ideal habitat for the species to rest while not foraging.

The kelp also provides cover from predators, such as gulls and skuas, which sometimes attack the shags.

Movements and Migration

The Stewart Island Shag is a resident bird, meaning that it does not migrate long distances. However, they are known to move between different parts of their range depending on the season and the availability of food.

During breeding season, which occurs in the summer, the Stewart Island Shags breed in colonies that are usually located on rocky islets and cliffs close to the water. In winter, the birds disperse to different feeding grounds along the coast, and many birds move to deeper waters in search of food.

Recently, researchers have been using tracking devices to learn about the movement patterns of the Stewart Island Shag. One study used GPS backpacks to track the movements of the birds, revealing that they forage up to 40 km away from their breeding colony during the non-breeding season.

They also found that the birds have specific feeding areas that they return to year after year, suggesting that they have a strong fidelity to their feeding grounds. The study also found that the foraging behavior of the Stewart Island Shag varied depending on the time of day.

The birds were most active and covered the longest distances during the early morning and late afternoon. During the midday, they rested on rocks and islets along the coast.

This behavior is likely due to the fact that the fish they prey on are more active during those times. Overall, while the Stewart Island Shag is not a migratory bird, it is still a highly mobile bird that moves through different habitats depending on the season and the availability of food.

Conservation

The Stewart Island Shag is considered to be a species of least concern by the International Union for

Conservation of Nature. However, the species is still vulnerable to habitat degradation, disturbance, and predation.

There are several conservation actions that could be taken to ensure the long-term survival of the species. One action would be to protect and restore kelp beds along the New Zealand coast.

This would provide the birds with much-needed habitats for foraging and nesting. The New Zealand Department of

Conservation has also implemented measures to control the population of introduced predators, such as rats and stoats, which pose a threat to the Stewart Island Shag’s populations.

Finally, researchers have stressed the importance of monitoring the movements and populations of this species to ensure their long-term survival. Through GPS tracking and other methods, scientists can learn more about the Stewart Island Shag’s behaviors and habitats, helping to inform future conservation efforts.

Conclusion

The Stewart Island Shag is a unique and intriguing bird species that inhabits the southern regions of New Zealand. Their distinctive plumage and range of habitats make them a fascinating bird to observe.

While the species is not migratory, they are highly mobile and move between different habitats in search of food. To ensure the long-term survival of these birds, it is essential to protect their habitats, control invasive predators, and monitor the populations and movement patterns of the species.

By taking these measures, we can help to preserve the Stewart Island Shag for future generations.

Diet and Foraging

The diet of the Stewart Island Shag includes a variety of fish, crustaceans, and invertebrates that are found in their coastal habitats. These birds are excellent divers, and during foraging, they often swim underwater for several seconds, using their wings to propel themselves through the water.

They usually forage alone or in small groups of up to ten birds.

Feeding

The Stewart Island Shag feeds mainly on small fish such as sand lance, plaice, and flathead, and occasionally on crustaceans such as crabs. They capture their prey by diving underwater, using their sharp beaks to catch the fish once they spot them.

They can dive up to 12 meters in search of food, and they can remain submerged for up to 100 seconds.

Diet

The Stewart Island Shag’s diet is impacted by seasonal changes in the availability of prey. During the breeding season, which occurs in the summer, the birds feed on small fish, which are abundant in shallow coastal waters.

In winter, the birds disperse to deeper waters in search of food, where they feed on larger fish species and invertebrates. In addition, the Stewart Island Shag has an intraspecific competition for food.

Due to a decline in the population of kelp, which provides the ideal shelter for the fish species that the shags feed on, there has been a reduction in the available fish for the birds, leading to competition for resources.

Metabolism and Temperature Regulation

The Stewart Island Shag has unique adaptations that allow it to regulate its metabolism and body temperature. One adaptation, known as countercurrent heat exchange, is a mechanism in birds that helps prevent body heat from being lost through the legs and feet.

The shags have arteries that carry warm blood close to veins that return cool blood to the body, allowing for efficient heat exchange and conservation of body heat. In addition, these birds have a metabolic rate that is lower than similar-sized land birds and is more efficient at utilizing the energy from their food.

This adaptation enables the Stewart Island Shag to survive on a lower calorie diet, which is essential during the winter months when food availability is less predictable.

Sounds and Vocal

Behavior

The vocalization of the Stewart Island Shag is characterized by a range of croaks, rattles, and screeches. These sounds are used for communication between birds, particularly during the breeding season.

Vocalization

During the breeding season, male shags use their vocalizations to attract females and establish their territory. The males perform a courtship display that involves bowing, bill fencing, and vocalizations, and the male and female birds will continue to vocalize throughout the breeding season to coordinate their efforts in nest building, incubation, and feeding their young.

Researchers have noted that the calls of the Stewart Island Shag are relatively low in frequency compared to other cormorant species. Additionally, the frequency and repetition rates of the vocalizations vary depending on the context and the birds’ social behaviors.

Conclusion

The Stewart Island Shag’s behavior is tailored to its unique coastal habitat. These birds are efficient divers and forage on a diet dominated by fish, with intraspecific competitions for food.

Their metabolic rates are adapted to the low-calorie diets of the winter months, and their body temperature is efficiently regulated using countercurrent heat exchange. Finally, the shags vocal behavior includes a range of croaks, rattles, and screeches used for communication, including during courtship displays, territory establishment, and coordination of activities during the breeding season.

Behavior

The Stewart Island Shag is a highly adaptable species that exhibits a range of behaviors suited to its coastal habitat. Their behavior includes locomotion, self-maintenance, agonistic behavior, and sexual behavior.

Locomotion

The locomotion of the Stewart Island Shag is predominantly through swimming and diving. When swimming, the birds use a smooth gliding motion, using their wings to provide propulsion.

When diving, the shags use their wings to swim underwater and catch prey.

Self Maintenance

The Stewart Island Shag engages in a range of self-maintenance behaviors, including preening, bathing, and sunbathing. Preening is a behavior the bird performs to maintain its feathers, which it does by using its bill to groom and clean its feathers.

Bathing behaviors also help to maintain the feathers, removing dirt and excess oil. Agonistic

Behavior

Agonistic behavior refers to any behavior intended to resolve conflicts between individuals.

The Stewart Island Shag exhibits agonistic behavior during territorial disputes, mainly during the breeding season. Sexual

Behavior

During the breeding season, male Stewart Island Shags perform courtship displays to attract females.

The displays include bill-fencing, bowing, and vocalizations, where males vocalize their distinctive calls to establish territories and attract females. Once a female has accepted a male’s courtship display, the pair begins to build a nest together.

Breeding

Breeding in the Stewart Island Shag occurs during the late summer months, with eggs typically laid in January and February. The birds build their nests on rocky cliffs, islets, and campsites.

The nests are made up of sticks and vegetation and are lined with small twigs, grasses, and feathers. Stewart Island Shags typically lay two eggs, with incubation lasting around 30-31 days.

Both male and female birds take turns incubating the eggs, and both are responsible for feeding and caring for the chicks.

Demography and Populations

The Stewart Island Shag’s demography and population are challenging to estimate due to the limited range of the species and their habitat preferences. However, recent studies suggest that the population size of the species is declining due to habitat loss and predation by invasive mammalian species, such as rats and stoats.

The Stewart Island Shag’s population in the Chatham Islands, in particular, is under threat, with the L. c.

stictocephalus subspecies listed as critically endangered by the IUCN. The subspecies purpurascens, which is found on the Snares Islands, has also experienced a decline in population size.

Efforts are currently underway to protect the Stewart Island Shag’s population, including controlling the population of introduced mammalian predators and habitat restoration initiatives. Monitoring the population and demographic trends of the species is also essential to better understanding the challenges it faces and developing effective conservation strategies.

Conclusion

The Stewart Island Shag’s behavior is well-suited to its specific coastal habitats, exhibiting adaptive behaviors such as swimming, diving, and preening. During the breeding season, the species displays courtship and territorial behavior.

Breeding occurs through incubating eggs where both parents share the duties of feeding and caring for the chicks. Finally, the population of the Stewart Island Shag is declining in certain subspecies, highlighting the need for conservation actions to protect this unique and important coastal bird species.

The Stewart Island Shag

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