Great Shearwater Life Cycle: Nest Building To Fledging (and everything in between)
The Great Shearwater (Ardenna gravis) is one of the most remarkable seabirds in the world, known for its incredible transequatorial migration that spans thousands of miles across the Atlantic Ocean.
These oceanic wanderers breed on remote islands in the South Atlantic and then embark on an extraordinary journey that takes them as far as the waters off the UK coast.
In this article, let’s have a closer look into the life cycle of the Great Shearwater, from nest building to fledging and beyond!
Table of Contents
How Long Does A Great Shearwater Live?
Great Shearwaters typically live between 15 to 20 years in the wild.
Their survival depends heavily on ocean conditions, food availability, and their ability to navigate the challenges of their extensive migrations. While predation at sea is relatively rare for adult birds, they face various threats including plastic pollution, fishing gear entanglement, and changes in ocean temperatures affecting their food sources.
Climate change and its impact on marine ecosystems pose significant challenges to these birds’ longevity, particularly affecting their ability to find food during their long distance migrations.
How Fast Can A Great Shearwater Fly?
Great Shearwaters can reach speeds of 30 to 40 miles per hour (48 – 64 kilometres per hour) during regular flight. However, when riding ocean winds and currents, they can achieve even higher speeds.
These birds are exceptionally skilled fliers, using a technique called dynamic soaring to conserve energy during their long migrations. They take advantage of wind gradients above the ocean surface, alternating between high and low elevations to maintain momentum with minimal energy expenditure.
Their flight pattern is characterised by long glides just above the waves, followed by banking turns that showcase their mastery of oceanic conditions. This efficient flying technique enables them to cover vast distances during their annual migrations across the Atlantic.
Are Great Shearwaters Aggressive?
Great Shearwaters are generally not aggressive birds, but they can display competitive behaviour when feeding in groups. During these gatherings, they may engage in noisy disputes over food, particularly when scavenging behind fishing vessels.
At their breeding colonies, they become more territorial, especially when defending their burrows. However, their aggression is typically limited to vocalisations and threat displays rather than physical confrontations.
These birds are known to be quite social when gathering in feeding groups at sea, where they can form large flocks numbering in the hundreds or even thousands.
What Is A Great Shearwater’s Habitat?
Great Shearwaters are pelagic birds, meaning they spend most of their lives at sea in the open ocean. They only come to land to breed, choosing remote islands in the South Atlantic, particularly Nightingale Island and other islands in the Tristan da Cunha archipelago.
These birds are highly adapted to marine environments, capable of drinking saltwater and extracting the salt through specialised glands. They prefer productive ocean waters where upwelling brings nutrients to the surface, supporting abundant fish and squid populations.
How Long Does It Take For A Great Shearwater To Build A Nest?
Great Shearwaters typically take 3 to 5 days to construct their nests. These seabirds are burrow nesters, either digging their own burrows or modifying existing ones in the soft soil of their breeding islands.
The nests are usually simple scrapes at the end of burrows that can extend up to 2 metres in length. Both parents participate in the burrow excavation and nest preparation, working predominantly at night to avoid predation.
These nocturnal activities help protect them from predators such as skuas and gulls that might otherwise prey on the adults or their eggs.
Eggs
The egg laying phase is a crucial period in the Great Shearwater’s breeding cycle, occurring in remote island colonies far from human observation.
When Do Great Shearwaters Lay Eggs?
Great Shearwaters lay their eggs between October and November in the Southern Hemisphere. This timing coincides with the austral spring, when conditions are optimal for raising chicks.
The breeding season is highly synchronised within colonies, with most pairs laying eggs within a few weeks of each other. This synchronisation helps maximise the chances of survival for the chicks by ensuring they fledge when food availability is highest.
How Many Eggs Does A Great Shearwater Lay?
A Great Shearwater lays only one egg per breeding season. This single egg strategy is common among seabirds and reflects the significant investment required to raise a chick successfully in challenging oceanic conditions.
If the first egg is lost early in the season, the pair may attempt to lay a replacement egg, but this is relatively rare. The single egg strategy allows parents to invest maximum resources in raising one healthy chick rather than dividing their efforts among multiple offspring.
What Do Great Shearwater Eggs Look Like?
Great Shearwater eggs are large and oval shaped, measuring approximately 75 to 80 mm in length. They are white in colour, sometimes with fine reddish brown speckles, particularly at the larger end.
The egg’s shell is relatively thick, providing protection in the burrow environment. The size of the egg is quite substantial relative to the adult bird’s body size, representing a significant energy investment by the female.
How Long Do Great Shearwater Eggs Take To Hatch?
Great Shearwater eggs take approximately 53 to 57 days to hatch. During this extended incubation period, both parents take turns incubating the egg, typically in shifts lasting several days.
The long incubation period is characteristic of pelagic seabirds and allows for full development of the chick before hatching.
Chicks
Great Shearwater chicks undergo a remarkable transformation from helpless hatchlings to ocean going birds capable of transoceanic migration.
How Many Chicks Does A Great Shearwater Have?
A Great Shearwater pair raises one chick per breeding season. This single chick strategy allows parents to focus all their energy and resources on successfully raising one offspring.
The survival rate of chicks varies depending on factors such as food availability and weather conditions. Both parents contribute to feeding and caring for their single chick, making regular foraging trips to sea to gather food.
When Do Great Shearwater Chicks Open Their Eyes?
Great Shearwater chicks open their eyes within 24 to 48 hours after hatching. This relatively quick eye opening is essential for their survival in the dark burrow environment.
The chicks are born semi altricial, meaning they are relatively well developed at hatching but still require extensive parental care. Their early ability to see helps them recognise and respond to their parents during feeding.
When Do Great Shearwater Chicks Fledge?
Great Shearwater chicks fledge after approximately 80 to 90 days in the nest. During this period, they develop their flight feathers and gradually lose their down feathers.
The fledging period is crucial as the chicks need to reach a healthy weight and develop strong flight muscles before leaving the nest. Once they fledge, young Great Shearwaters immediately head out to sea, where they will spend the next several years before returning to breed.
SEE ALSO: Great Shearwater Diet and Size: Feeding Habits, Predators, and Measurements
Frequently Asked Questions
Great Shearwaters primarily feed on small fish, squid, and crustaceans. They catch their prey by either surface seizing or plunge diving up to 2 metres deep.
Great Shearwaters can be seen in UK waters from August to October, particularly off the southwest coast during their northern migration.
Great Shearwaters undertake one of the longest migrations of any bird, traveling over 14,000 kilometres in a figure of eight pattern across the Atlantic Ocean.
