Shearwaters: flight apparatus
Wing
The shearwater wing consists of 11 bones:
The arm part (4 bones): humerus (1) and ulna/radius (3&4) are nearly of the same length and are rather long to the hand wing. A sesamoid or spreader bone (2) is situated in the pit of the elbow which is connected to the ectepicondylar process of the humerus by a ligament, forming a supporting structure for the patagial fan in the outstreched wing. This is also found in other petrels and albatrosses, with the exception of the Fulmarines, Prions and Blue Petrel.
The hand wing consists of 
the radiale and ulnare (5): two small bones in the wrist, carpometacarpus (6), alula (7) and the digits (8).
In the more aerial species, such as Calonectris the arm part is proportionally longer than in the more aquatic species such as the Sooty Shearwater Ardenna grisea and the Manx's group. The diving habits of the latter require shorter and stronger bones. All wing bones, but most strikingly the humerus, are stronger built and somewhat flattened to provide streamline and more strength to cope with the forces to which the wing is submitted during underwater propulsion by the wings. In the aerial species the humerus is more rounded and slenderer.
Similarly sized humeri showing the difference in flatness in the more aerial Wedge-tailed Shearwater Ardenna pacifica (upper) and the more aquatic Short-tailed Shearwater Ardenna tenuirostris (lower).
Sternum, coracoid and furcula
The sternum or breastbone of a shearwater is, depending on the species, variable in size and shape. It is somewhat constricted in the middle and has four distal notches [in individual cases two or up to six]. The processes form a frame to a flexible membrane that protects the intestinals. The more aerial species in which a gliding flight dominates have a relatively small, short, ‘square’ and pneumatized sternums: one to a few cavities at the base of the keel in the middle interior side. The 'squarish' shape implicates relatively small and short flight musculature, more suited for static forces. The diving species have proportionally large, elongated and non-pneumatized sterna to provide a basis to the large and longer flight muscles that are needed for underwater propulsion. Sternum, coracoids and furcula are lighter built in the aerial species compared with their diving kin. The pictures below show the differences between te species, all at the same scale.
N.B. The differences are clear, but be careful using them as an identification aid; there is variation in size and a little bit in shape within species. The bends in the keels of some sterna shown here arise after cleaning and drying the specimens. In live birds it is normally straight.
Calonectris
Calonectris shearwaters are gliders and don't dive very deep. As a result they have rather short sterna. Shortest in C. leucomelas wich is the the most aerial of all.
Streaked Shearwater Calonectris leucomelas
Scopoli's Shearwater Calonectris (d) diomedea
Cory's Shearwater Calonectris (d) borealis
Cape Verde Shearwater Calonectris edwardsii
Ardenna
Buller's and Wedge-tailed shearwaters are the most aerial Ardenna species. Sooty and Short-tailed the most aquatic. Sooty is capable of very deep dives and has a very large sternum. Flesh- and Pink-footed and Great are comparable with the Calonectris species in this respect, good gliders but moderate divers and sit in de middle range. 
Buller's Shearwater Ardenna bulleri (Thyellodroma)
Wedge-tailed Shearwater Ardenna pacifica (Thyellodroma)
Sooty Shearwater Ardenna grisea (Neonectris)
Short-tailed Shearwater Ardenna tenuirostris (Neonectris)
Great Shearwater Ardenna gravis (Ardenna)
Pink-footed shearwater Ardenna c. creatopa (Hemipuffinus)
Flesh-footed Shearwater Ardenna (c.) carneipes (Hemipuffinus)
Puffinus
Puffinus shearwaters are capable divers and have proportionally large keels and long sterna with long
extensions to support the protective membrane, similar to the Sooty and Short-tailed Shearwater.
Manx's Shearwater Puffinus puffinus
Yelkouan or Levantine Shearwater Puffinus yelkouan
Balearic Shearwater Puffinus mauretanicus
Fluttering Shearwater Puffinus gavia
Hutton's Shearwater Puffinus huttoni
Subantarctic Shearwater Puffinus elegans
Baroli's Shearwater Puffinus baroli