ハイイロミズナギドリ 対 ヨーロッパミズナギドリ

The most reliable field mark to separate Sooty Shearwater from Balearic Shearwater is the overall darkness and the presence of a silvery underwing panel in Sooty, compared to the more contrasting, two-toned appearance of Balearic. Sooty Shearwater appears uniformly dark brown to nearly black in most lights, with only a subtle silvery stripe on the underwing, while Balearic is distinctly paler below, with dirty white underparts and a sharp contrast with the dark upperparts. In flight, Sooty looks like a small albatross with stiff, straight wings and a powerful, direct flight, whereas Balearic shows a more classic 'flying cross' look, with wings held at right angles and a more contrasting plumage as it banks. Size is also a clue: Sooty is noticeably larger and longer-winged than Balearic. If you see an all-dark shearwater with only a faint underwing contrast, especially in the Atlantic, it's almost certainly a Sooty; a bird with clear dark upperparts and pale underparts is Balearic.

1. Overall darkness: Sooty Shearwater is uniformly dark brown to blackish above and below, with only a subtle silvery underwing panel; Balearic always shows a strong contrast between dark upperparts and pale, dirty white underparts. This is the single most reliable field mark for all ages and seasons.
2. Underwing pattern: Sooty has a silvery stripe along the center of the underwing, but the rest of the underwing is dark; Balearic's underwing coverts are pale, matching the belly, and create a much more contrasting look in flight. If you see a pale underwing with a dark border, it's Balearic; if the underwing is mostly dark with just a silvery panel, it's Sooty.
3. Flight style and jizz: Sooty flies with stiff, straight wings and a powerful, direct flight, often looking like a small albatross. Balearic's flight is more buoyant, with wings held at right angles, and it often banks to show off the contrast between upper and underparts.
4. Size: Sooty is noticeably larger and longer-winged than Balearic. If seen together or among other shearwaters, Sooty stands out as bulkier and more robust.
5. Plumage in poor light: Sooty can appear all-black in dull conditions, which is never true for Balearic, which always shows some underpart contrast.
6. Plumage in good light: In bright conditions, Sooty's chocolate-brown tones and silvery underwing stripe become visible, while Balearic's pale underparts and underwing coverts are obvious.
7. Age and molt: No distinctive juvenile or immature upperwing patterns are described for either species, so age does not affect the main separation marks.
8. Habitat and range: In the Atlantic, a large, all-dark shearwater is almost certainly Sooty, as Balearic is smaller and always two-toned. In the Mediterranean, Balearic is the expected species, but Sooty can occur as a rare vagrant.
9. Group association: Sooty often occurs in large, dense flocks, especially during migration; Balearic is more often seen in smaller groups or singly.
10. Confusion with other species: Sooty can be confused with other large, dark shearwaters in the Pacific, but in the Atlantic, only Balearic is likely to cause confusion at range. The key is the underpart contrast.
11. Bill and head shape: Not described as diagnostic in the notes; focus on plumage and size.
12. Tail and primary projection: Not described as diagnostic; both have typical shearwater proportions.
13. Voice: Not useful at sea; both are silent away from breeding colonies.
14. Seasonal context: Sooty is present in the North Atlantic mainly in the northern summer and autumn; Balearic is present year-round in the Mediterranean and adjacent Atlantic.
15. When in doubt: If you cannot see underpart contrast and the bird looks all-dark, favor Sooty; if you see a clear pale belly and underwing, it's Balearic.

Sooty Shearwater is significantly larger, measuring 40–51 cm in length with a wingspan of 94–110 cm [wikipedia]. Balearic Shearwater is smaller, at 34–39 cm long and a wingspan of 78–90 cm [wikipedia]. This size difference is often visible in direct comparison or when seen among mixed flocks, with Sooty appearing longer-winged and bulkier overall.

For all ages, Sooty Shearwater is dark chocolate-brown to nearly black overall, with a distinctive silvery stripe running along the center of the underwing. In dull light, it can look entirely blackish, but the underwing panel is usually visible in good conditions. Balearic Shearwater, by contrast, always shows a strong two-toned effect: dark brown upperparts and much paler, dirty white underparts, including the underwing coverts. This contrast is especially obvious in flight, as Balearic's underwing and belly flash pale against the dark upperparts. Sooty never shows this level of contrast below. No age-specific upperwing patterns are noted for either species, but the overall darkness of Sooty (with only the subtle silvery underwing) is consistent across ages, while Balearic's pale underparts are present in all plumages. In poor light or at great distance, Sooty can appear all-dark, which is never true for Balearic.

Both species share the typical 'shearing' flight style of the genus, gliding low over the water with stiff, slightly arched wings and few wingbeats. Sooty Shearwater, however, has a more powerful and direct flight, often giving the impression of a small albatross, with wings held stiff and straight. Balearic Shearwater tends to look more like a flying cross, with wings at right angles to the body, and its banking flight accentuates the underpart contrast. Both species dip from side to side, but Sooty often appears steadier and more purposeful, while Balearic may look more buoyant and less forceful.

Sooty Shearwater is a global migrant, breeding in the southern oceans and ranging widely into both the Pacific and Atlantic, often seen far offshore in large flocks. Balearic Shearwater is much more localized, breeding only in the Balearic Islands and foraging mainly in the western Mediterranean and nearby Atlantic. In the Atlantic, Sooty is the only large, all-dark shearwater, while Balearic is restricted to the northeast Atlantic and Mediterranean. Context can help: a large, dark shearwater far offshore in the North Atlantic is likely Sooty, while a smaller, two-toned bird in the western Med or near Iberia is likely Balearic.

Both species are mostly silent at sea. Sooty Shearwater is vocal at night on breeding grounds, producing loud coos and croaks, but these are not heard at sea. Balearic Shearwater's voice is not described in the field notes for sea-watching contexts. Vocalizations are not useful for separating these species at sea.