The Great Shearwaters (Puffinus gravis) is a large shearwater in the seabird family Procellariidae. Its relationships are unclear. It belongs to the group of large species that could be separated as genus Ardenna (Penhallurick and Wink 2004); within these, it might be allied with the other black-billed, blunt-tailed species, Short-tailed Shearwater and especially Sooty Shearwater (Austin 1996, Heidrich et al. 1998).
Alternatively (Austin 1996, Austin et al. 2004), it could be a monotypic (one single species) subgenus (Ardenna sensu stricto), an Atlantic representative of the light-billed Hemipuffinus group (Pink-footed shearwater and Flesh-footed Shearwater).
Behaviour
A highly social seabird (Puffinus Gravis), the Great Shearwater often flies and feeds in large groups. You can often see them gliding in front of ships, looking for food scraps. Wind currents allow them to glide effortlessly for long periods of time without a single wing flap.
The name is derived from the way they fly. They “shear”, just above the surface of the ocean, with their wings spread, and follow the rises and falls of the waves. Birdwatchers will enjoy this beautiful sight.
The Great Shearwater is an excellent swimmer, using its wings as underwater flippers to turn, steer and even spin while chasing prey below the waves. On land, however, they are quite awkward, clumsy and waddle instead of walking.
The birds migrate across the equator every year. The birds breed in the Southern Hemisphere and then migrate north to the Northern Hemisphere during the non-breeding season. They travel thousands of kilometres on their epic journeys.
Their calls are loud, varied and varied. When they feed, they squawk loudly and, at night, make croaky noises near their nests. The males and females have different sounds, which is a nice feature for their social life.
It’s interesting to note that, unlike other seabirds, Great Shearwaters do not need to hide during the night. They are relatively safe due to their size from predators such as skuas, and they can be vocal and active during daylight.
Distribution / Range
Great Shearwater species breeds on Nightingale Island, Inaccessible Island, Tristan da Cunha, and Gough Island. It is one of only a few bird species to migrate from breeding grounds in the Southern Hemisphere to the Northern Hemisphere, the normal pattern being the other way around.
This shearwater nests in large colonies, laying one white egg in a small burrow or in the open grass. These nests are visited only at night to avoid predation by large gulls.
This shearwater, like the Sooty Shearwater, follows a circular route, moving up the eastern seaboard of first South and then North America, before crossing the Atlantic in August.
It can be quite common off the southwestern coasts of Great Britain and Ireland before heading back south again, this time down the eastern littoral of the Atlantic. According to BirdLife International, this species is well documented.
Description
This bird has the typical “shearing” flight of the genus, dipping from side to side on stiff wings with few wingbeats, the wingtips almost touching the water. Its flight is powerful and direct, with wings held stiff and straight. According to Audubon Society, this species is well documented.
This shearwater is 43-51 cm in length with a 105-122 cm wingspan. It is identifiable by its size, dark upperparts, and underparts white except for a brown belly patch and dark shoulder markings. It has a black cap, black bill, and a white “horseshoe” on the base of the tail. The stiff flight, like a large Manx Shearwater, is also distinctive.
The only other large shearwater in its range is the all-dark Sooty Shearwater.
Diet / Feeding
Great Shearwaters eat mainly fish, squid, but will also snack on crabs and fishing boat scraps. When food is present, they are known to squabble loudly.
There are several ways they hunt. One is plunge-diving–diving from heights of 6-10 metres into the water, sometimes pausing mid-air before diving headfirst. They often take off again after diving.
They also use Surface-seizing, which makes it look like they are “walking on the water”. They land on the surface with their wings spread to balance themselves. This is a fascinating behaviour to observe.
They are lively seabirds because of their feeding habits. Birdwatchers will enjoy watching them glide and dive from the shore or boat.
Calls / Vocalisations
They have a piercing eeyah cry, usually given when resting in groups on the water.
Conservation Status
Despite being common, Great Shearwaters are facing increasing conservation concerns. Millions of breeding pairs are found on Tristan da Cunha and Gough Island.
Annual Harvesting by Tristan Islanders, including thousands of adults and up to 50,000 young chicks, could become unsustainable. Populations may start to decline without proper limits.
Bycatch can also pose a threat, since birds may be caught accidentally when diving to find bait. It is important to adopt bird-friendly practices for fishing and conduct further research.
More studies on the breeding habits, migration patterns, and long-term impacts of harvesting are required to protect these incredible seabirds. Conservation efforts will ensure that they are a common sight above the sea for many generations to come.
