Procellariidae

Shearwaters: Puffinini

Genus Calonectris

• Streaked Shearwater Calonectris leucomelas; seas around Japan, western Pacific Ocean.

• Cory's Shearwater Calonectris diomedea

•   Cory’s or Atlantic Shearwater Calonectris diomedea borealis;  Atlantic Ocean, incidentally Mediterranean Sea.

•   Scopoli’s or Mediterranean Shearwater Calonectris diomedea diomedea; Mediterranean Sea, Atlantic Ocean. 

• Cape Verde Shearwater Calonectris edwardsii, Cape Verde Islands, Atlantic Ocean.

Evolution and taxonomy

All species of this group are northern hemisphere breeders. Formerly two species were recognized, but during the last decades there was a tendency to split the Cory's shearwater into three separate species, which was not supported by all authors. Penhallurick and Wink (2004) returned to the two species concept and proposed to consider Cory's and Scopoli's again as subspecies of C. diomedea. They did not include the Cape Verde Shearwater in their analysis, but list it as a third subspecies of C. diomedea. A recent study by Gómez-Diaz et al. (2006) on the phylogeography of Calonectris, based on molecular and morphometric data, doesn't support this vision. They consider C. edwardsii as a separate species.
This study shows that the Calonectris species complex is an early split from the shearwater lineage, about 13.8 to 9 My ago (Penhallurick & Wink, 2004, Gómez-Diaz et.al 2006). C. leucomelas diverged about 3 My ago, which coincides with the emerging of the Panama land bridge, separating the Atlantic and Pacific populations. The Atlantic population started to split up much more recently, about 1 My ago. C. edwardsi is estimated to have separated from the Mediterranean population about 700.000 years ago. Fossil remains of Calonectris (C. krantzi) are known from South Africa and South Carolina and date back to 5 My ago. (Olson 1985a, 1985b)
 

Distribution

The Streaked Shearwater breeds mainly around Japan and migrates during the winter to the south-western Pacific, as far as northern Australia.
The Palearctic group contains the Cory's, Scopoli's and Cape Verde shearwater. The first breeds on the Macaronesian Islands (Canaries, Madeira, Azores) and the Berlenga's off Portugal. The border line between the Atlantic and Mediterranean subspecies lies close to the Strait of Gibraltar and corresponds with the Almerian-Oran Oceanic Front, being the real boundary between the Atlantic and Mediterranean surface waters. True Cory's have been found breeding in Almería on the Mediterranean coast of Spain. Some interbreeding has been reported, and interesting is the fact that in recent years the Mediterranean race established a small colony at the French Atlantic coast west of Bordeaux (DBA, WP reports 2006).
The Cape Verde Shearwater is an endemic of the Cape Verde Islands and doesn't move over great distances.
The winter distribution and migrating of the Cory's follows a route to South and North America. The Scopoli's mainly follows the African coast and concentrates near South Africa.

Behaviour

Due to their close realationship the behaviour of all taxa is very similar. Their dominant flight pattern is typical for larger tubenoses: a few slow and shallow wing beats, followed by a glide close to the surface of the sea in normal stuations. Depending on the wind conditions they can vary between this way of flying to dynamic soaring like a small albatross. The foraging strategy is mainly surface seizing of small fish and squid. Although not being the most aquatic species, diomedea is capable of diving to a maximum of about 15 meter and leucomelas at least 5 to 7m (Oka 1994, Matsumoto 2005). When diving the wings are folded to a certain extend and wings and feet are used for propulsion simultaneously. Under water Calonectris species are not very agile compared with other shearwaters. Like most other procellariiforms Calonectris species are not good walkers.
Calonectris shearwaters are burrow breeders, using natural cavities in volcanic rock, remains of old buildings, but also dig their own burrows when nescessary.     
   

Osteology

The skeleton of all species is very similar. They differ mainly in size, but the proportions are the same. The present populations of the Palearctic show remarkable size differences, not only between the different taxa, but even within the taxa. The Scopoli's shows an east west cline with slighly larger birds in the western Mediterranean, and the larger Cory's, less prominent, a size increase from south to north. Unlike other shearwater species the Scopoli's and Cory's shearwater show also considerable differences between the sexes, males being larger than the females. The Cape Verde Shearwater follows the rule that body size in procellariform species decreases towards tropical areas. In the Streaked Shearwater the sexes differ not much in size.

 
The skulls are also very similar in structure. All of them having long bills with nostrils of about 1/5 of its length and a somewhat ‘flat’ cranial profile.
The skull of the Streaked Shearwater averages a bit smaller with a more slender bill than in Cory's and Scopoli's. The ramphotecal coating is greyish horn colored instead of the yellow bills of its Atlantic and Mediterranean counterparts.
Skulls of both diomedea subspecies overlap in measurements, but borealis averages larger and differs by being more robust. Sexes do overlap too, but in in borealis and diomedea there is a marked difference in average size, males being larger. Both have yellowish bills with blackish markings at the tip.
The bill of borealis often said to be heavier built than in diomedea. After calculating the bill ratio (culmen length :  height at nostrils)  of over 50 Cory's and about 20 Scopoli's (from museum specimens)  this appears to be true for most  - but not all - males. The females just have bigger bills (own research). When comparing the the cranium of both species the Mediterranean Scopoli's is slightly more slender built than the Cory's.
The skull of the Cape Verde Shearwater is much smaller and has a darker brownish bill, also with blackish markings at the tip. All Calonectris shearwaters have a whitish apex to their bill tips.

Streaked Shearwater Calonectris leucomelas Kamakura, Honshu, Japan Culmen: 51.9 mm; total: 106.9 mm, adult male
Scopoli’s Shearwater  Calonectris diomedea diomedea,  Mediterranean Sea Culmen: 53.4 mm; total: 108.9 mm, adult male
Cory’s Shearwater Calonectris diomedea borealis,  Pico, Azores Culmen: 58.1 mm; total:  118.6  mm, adult male.
Cape Verde Shearwater Calonectris edwardsii  Location unknown Culmen: 41.7 mm; total: 90.2 mm, adult, unsexed adult, probably female

Osteology

Sternum	Leg

Literature

• Brooke, M., 2004, Albatrosses and Petrels across the World, Oxford University Press, Oxford
• Gómez-Diaz, E. et al., 2006, Phylogeography of the Calonectris shearwaters using molecular and morphometric data, Molecular Phylogenetics and Evolution, Vol. 41, #2, 322-332
• Matsumoto, K., 2005, Foraging behaviour of Streaked Shearwater in Japan, Abstracts of oral presentations, 32nd Annual Meeting Pacific Seabird Group, Portland OR USA, 19-22 january 2005
• Oka, N., 1994, Underwater feeding of three shearwaters: Pale-footed (Pufinus carneipes), Sooty (Puffinus griseus) and Streaked (Calonectris leucomelas) Shearwaters. Journal of the Yamashina Institute for Ornithology 26: 81-84
• Olson, S.L, Rasmussen, P.C.,1985a Miocene and Pliocene birds from the Lee Creek Mine, North Carolina, In Avian Biology, Vol. VIII ed. by Farner, D.S. et al. Acedemic Press, New York
• Olson, S.L. ,1985b, An early Pliocene marine avifauna from Duinfontein, Cape Province, South Africa, Ann.S. Afr. Mus, 95 (4), 1985: 147-16
• Penhallurick J. & Wink M., 2004, Analysis of the taxonomy and nomenclature of the Procellariiformes based om complete nucleotide sequences of the mitochondrial cytochrome b gene, Emu, 2004, 104, 125-147

Photos

Upper: Cory's Shearwater at Selvagem Grande © Hans Bister

Middle: Streaked Shearwater, mounted specimen Ibaraki Museum. Nat. Hist., Japan, E. Soldaat

Photos skulls: E. Soldaat

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