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Cory's Shearwater - BirdForum Opus

Cory's Shearwater (subspecies C. d. borealis)
Photo © by katastrofa
Atlantic Ocean off Valle Gran Rey, La Gomera, Canary Islands, February 2019

Includes Scopoli's Shearwater

Calonectris diomedea

Identification

Cory's Shearwater (subspecies C. d. borealis)
Photo © by charelli
Azores

C. d. diomedea (Scopoli's Shearwater): Length 45-52 cm (17¾-20½ in), wingspan 112-122 cm, weight 560-730 g.
C. d. borealis (Cory's Shearwater): Length 50-56 cm (19¾-22 in), wingspan 118-126 cm, weight 817-956 g.
Light brown upper parts, white below, yellow bill with dark subterminal band, broad wings held bowed, heavy build, leisurely flight style with fewer wingbeats than other shearwaters.

Variation: the two subspecies differ slightly in plumage, with C. d. diomedea showing a little less black in the hand of the underwing due to white inner webs on the primaries, slightly smaller bill which is a little paler, overall slightly paler; the lesser overall size is not noticeable in the field. The average difference between these two forms is difficult to use because of much individual variation. More identification discussion in reference 6[6].

Similar Species

Cory's Shearwater (subspecies C. d. borealis)
Photo © by Glen Tepke
Atlantic southeast of Hatteras, North Carolina, USA, August 2008

Cape Verde Shearwater is very similar, but slightly smaller and with a slenderer bill and relatively longer tail.
Great Shearwater is about the same size with darker wings and body, smaller bill is black, narrow straight wings, capped appearance, smudgy brown on belly (sometimes faint), and white collar.
Manx Shearwater is much smaller with blacker upperparts, and pure white belly and undertail coverts.
Balearic Shearwater is much smaller with browner underparts.

Distribution

Breeds on Atlantic islands between 28°N and 40°N, on the coast in Iberia, and on islands in the Mediterranean Sea. Post-breeding dispersal takes especially birds of subspecies borealis north of the breeding range, for example to northern Europe and to western Atlantic. Winter is spent at sea, most birds migrate to the south Atlantic and the southwest Indian Ocean.

Taxonomy

Scopoli's Shearwater (subspecies C. d. diomedea)
Photo © by stu78
Kos, Greece, June 2009

Cape Verde Shearwater was formerly included in Cory's Shearwater.

Subspecies

Two subspecies are accepted by Clements,[1] treated as distinct species by most other authorities.[2][3]

  • C. d. diomedea - (Scopoli's):
  • Breeds Mediterranean islands
  • C. d. borealis - (borealis):

Habitat

Breeds on rocky islands and steep cliffs.

Behaviour

Breeding

Colonial breeders and ground nesters; 1 egg is laid.

Diet

The diet includes molluscs and fish.

Vocalisation

Listen in an external program

References

  1. Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2018. The eBird/Clements checklist of birds of the world: v2018. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/
  2. IOC
  3. BirdLife International
  4. Collins Bird Guide ISBN 0 00 219728 6
  5. Identification essay about the two subspecies discussed here

Recommended Citation

External Links

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