Markham's Storm-Petrel Oceanodroma markhami
Version: 2.0 — Published October 29, 2020
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Markham's Storm-Petrel is a large species of the genus Oceanodroma. Like other Oceanodroma, it is a relatively small seabird with long, pointed wings that are held bent at the carpal joint, and a deeply forked tail. It is entirely dark sooty brown, except for pale grayish brown upperwing coverts that form a distinct pale bar across the surface of the wing.
The boreal migrant Black Storm-Petrel (Oceanodroma melania) is sympatric seasonally with Markham's Storm-Petrel, and is very similar in size and appearance. However, Markham's has a shorter neck, squarer head, long bill, more deeply forked tail, a more extensive pale upperwing bar, and much shorter tarsi, which are best seen while foraging (2, 3, 4). Markham's also prefers cooler water and has shallower wingbeats than Black.
The dark-rumped "Chapman's" form of Leach's Storm-Petrel (O. leucorhoa chapmani) also may overlap with Markham's off of Ecuador, although they generally have a more northern distribution. "Chapman's" is about two-thirds the size of Markham's, and has shorter wings and a less deeply forked tail. Its flight is also much more bounding, with deep wingbeats (although note that flight style can vary, as it is also influenced by wind conditions; 4).
Ashy (O. homochroa), Matsudaira's (O. matsudairae), Tristram's (O. tristrami), and Swinhoe's Storm-Petrels (O. monorhis) also are entirely dark brown with a pale wing bar, but are entirely allopatric.
Juvenile and Immature
There are no known morphological differences between adults and juveniles. In other species of storm-petrels, birds can be recognized in the hand using the shape of the tip of the feathers.
Birds are sooty black above, shading to blackish brown on the underparts; the head, neck and mantle have a plumbeous gloss in fresh plumage. The greater wing coverts and scapulars are paler, more gray brown, forming a distinct diagonal bar across the extended wing, which extends almost to the carpal joint, where it is broadest; this bar becomes paler with wear. The distal uppertail coverts may be paler than the back, creating slight contrast with the blackish tail. In fresh plumage, the subscapulars have narrow whitish edges. The underwing is blackish gray, and has a slight silvery sheen. Flight feathers are almost black, though the bases of the primary shafts may be white. The upperparts often appear tricolored, with a sooty brown back and lesser coverts, pale wing band, and blackish flight feathers. The underparts are blackish brown. Sexes are similar.
Little is known about molt in this species. In the populations of the colonies of Paracas, Arica, and Quiuña, molt is initiated between December-January and is completed in April-May. Second prebasic molt should be looked for from September-March (4).
Iris and Facial Skin
Iris is brown (2).
Tarsi and Toes
Total length: 210-240 mm. Wingspan ca. 530 mm (5).
Measurements below come from Murphy (2), and include overall range, male mean (n = 6), and female mean (n = 5).
Range 163-181 mm; male mean 172.7 mm, female mean 169.8 mm.
Range 87-97 mm; male mean 92.7 mm, female mean 89.4 mm.
Range 16.8-19 mm; male mean 18 mm, female mean 18.1 mm.
Range 23-25 mm; male mean 23.9 mm, female mean 24.2 mm.
Middle Toe and Claw
Range 23-25 mm; male mean 25.6 mm, female mean 25.1 mm.
Mean 53.1 g (n = 40; 6).