Cory's shearwater

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Kingdom: Animalia

Phylo: Chordata

Grade: Birds

Order: Procellariiformes

Family: Procellariidae, Leach, 1820

Species: C. borealis

Scientific name: Calonectris borealis (Cory, 1881)

Who has never heard of the famous shearwaters? Perhaps the best known bird by the Azorean people and certainly the most emblematic of the archipelago!

The Cory's Shearwater is a medium-sized bird that can be easily identified by its gray-brown coloration on the upper part and white on the underside. The beak is entirely yellow. It has a body length of about 50 cm and a wingspan that can reach 125 cm. Regarding weight, it can vary between 700 – 950g.

The Cory's Shearwater belongs to the order of Procellariiformes which includes several seabirds such as albatrosses, petrels and storm petrels.

All birds belonging to this order have tubular nostrils that allow them to expel the excess salt they acquired after ingesting seawater. They demonstrate pelagic habits and therefore inhabit the open ocean. The wings are long and narrow, thus minimizing the energy costs associated with the long flights they carry out. Their toes are joined by interdigital membranes and the posterior toe is poorly developed or even non-existent. The fact that they spend most of their life at sea and have their legs located further back on the body makes it quite difficult for them to make well-balanced bipedal progress. They are clumsy on land, eventually making use of their wings to aid locomotion.

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Figure 1 - Close up view of the Cory's shearwaters head.

The ability of these birds to be able to fly practically without flapping their wings depends on the fact that the wind speed is significantly lower near the waves than in the upper layers. The flight pattern is a series of broad ellipses gaining lift in the upper layers of air, followed by an upwind movement into the lower layers of air with less wind. Then they slide downwind, gaining momentum again.

The Cory's Shearwater normally spends the winter in the Southern Hemisphere mostly on the coast of Brazil and South Africa.

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Figure 2 - Few examples of species belonging to the Procellariiforme order.

Its conservation status in the Azores is described as Least Concern, which is currently home to more than 75% of the world's population.

They arrive to the Azores on February coming from the South Atlantic. The arrival of these birds to the archipelago is seen as a good omen for the Azorean people as it marks the arrival of spring. They are gregarious birds both on land and at sea, benefiting from groups of dolphins and tuna, thus managing to capture their prey (at shallow depths). They can live over 40 years and reach sexual maturity around 8/9 years old. After this time, they form monogamous couples, with the male and female taking turns in parental care, each staying around 6 to 8 days in the nest.

Mating occurs between the months of April/May, and it is during the month of June that only one egg is laid (revealing a low fecundity) which will take about 1 month to hatch. They normally nest in cavities and crevices in rocks, but also in rocky mounds and holes dug in the ground.

The young are born with a gray plumage that is gradually replaced by adult plumage until October.

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Figure 3 - A couple of Cory's Shearwater in their nest.

Juveniles perform their first flight at the end of October/beginning of November.

The Cory's Shearwater is a bird that breeds in practically all the islands of the Azores archipelago and in the Berlengas and Madeira archipelagos.

They feed mainly on pelagic fish and cephalopods.

Unfortunately, shearwaters face a lot of threats. In particular, the introduction of predatory mammals in the Azores meant that, with the exception of shearwaters, most of the procellariiformes were eliminated from the islands.

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Figure 4 - Reproductive cycle of the Cory's shearwater.

The main threats that shearwaters face today are:

  • Destruction of nesting habitat
  • Presence of predators and invasive plants
  • Running over and collision
  • Pollution (including light)
  • Bycatch in fishing gear
  • Capture for consumption or bait and vandalism
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Figure 5 - Cats are one of the main threats for Cory's shearwater in the Azores.

Reserve já a sua experiência na natureza dos Açores connosco here.

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