Table

 

Cory’s Shearwater – Accepted

1. 09 Aug 2003

 

~25 nmi. w Bodega Bay SON

2003-094

29

ph., NAB 58:175, San Miguel & McGrath (2005)

 

Cory’s Shearwater – Not accepted, identification not established

22–23 Aug 2003

 

Monterey Bay MTY

2003-099

30

 

 

 

 

 

Cory’s Shearwater

CORY’S SHEARWATER Calonectris diomedea (Scopoli, 1769)

Accepted: 1 (50%)

Treated in Appendix H: no

Not accepted: 1

CBRC review: all records

Not submitted/reviewed: 0

Color image: none

This shearwater’s nominate subspecies breeds on Mediterranean islands and winters primarily in the Atlantic Ocean off southern Africa. Small numbers encountered in the Red Sea may be misguided individuals attempting to migrate from the Indian Ocean back to the Mediterranean Sea (Shirihai 1996). The subspecies has been recorded as a spring and fall vagrant in the western Atlantic Ocean (Bull 1974), and more recent observations off the coast of North Carolina suggest that Cory’s Shearwater occurs there regularly in spring (San Miguel and McGrath 2005). Subspecies diomedea is best distinguished from C. d. borealis by the greater extent of white on the inner webs of the primaries. Members of borealis breed on islands of the northeastern Atlantic Ocean, are common between May and October off the Atlantic coast of North America (less commonly in the Gulf of Mexico and rarely in the Caribbean Sea), and winter off South America’s Atlantic coast, with substantial numbers reaching the southwestern Indian Ocean (Marchant and Higgins 1990). In the South Pacific, a beached specimen of borealis was recovered in January 1934 on New Zealand’s North I. (Marchant and Higgins 1990), and during the periods 23 March–19 October 2005 and 24 April–6 June 2006 a lone Cory’s Shearwater consistent with borealis was observed around the Islas Los Coronados in northwestern Baja California, including multiple observations of the bird on an empty nest (NAB 59:658, 60:441, 468). A third taxon—the Cape Verde Shearwater (C. edwardsii), which the AOU only recently recognized as a species distinct from C. diomedea (Banks et al. 2006)—breeds on the Cape Verde Islands, disperses to waters off west Africa, and on 15 August 2004 was recorded off Hatteras, North Carolina (Patteson and Armistead 2004, Robbins et al. 2006). Gutiérrez (1998) provided criteria for identifying these taxa at sea.

The state’s only Committee-endorsed record of Cory’s Shearwater involves a bird photographed on 9 August 2003 among thousands of Sooty Shearwaters assembled along a steep temperature gradient that had developed over Bodega Canyon, approximately 25 nautical miles off Bodega Head in Sonoma County. This individual showed extensively dark undersides to the primaries, consistent with borealis. The CBRC did not accept a second reported Cory’s later that month at Monterey Bay, Monterey County.

Cory’s Shearwater normally occurs over warm water, suggesting that the species may occasionally stray into the Pacific Ocean by way of the Indian Ocean. Another plausible mechanism would involve a bird in the Caribbean Sea or southwestern Gulf of Mexico (both areas where the species is exceptionally rare) being blown across either Panama or the Isthmus of Tehuantepec.