トモエガモ 対 アフリカコガモ

The most reliable field mark is the Baikal Teal's distinctive face pattern: even in females and juveniles, look for a pale spot at the bill base and a white throat angled back to the eye, lacking in Blue-billed Teal. In flight, Baikal Teal (all ages) shows a darker underwing leading edge and a green speculum with a less distinct cinnamon-cream border, while Blue-billed Teal has a glossy green speculum with crisp black and white borders. Baikal Teal is larger, longer-tailed, and bulkier than the daintier, short-tailed Blue-billed Teal. Female and juvenile Baikal Teal can be confused with Blue-billed Teal, but careful attention to face pattern, tail length, and wing details will separate them. Both species have spotted breasts, but the Baikal's spots are rounder and more defined.

1. Face pattern (all ages): Baikal Teal (female/juvenile) shows a pale spot at the base of the bill and a white throat that angles back to the eye, plus a distinct pale eyebrow bordered by a darker crown. Blue-billed Teal lacks these pale face marks, instead showing a less contrasting, more uniform pale face with a dark brown crown and a blackish ear patch in males.
2. Tail length: Baikal Teal is longer-tailed and appears more elongated at rest and in flight; Blue-billed Teal is short-tailed and compact.
3. Underwing pattern (all ages): Baikal Teal has a darker leading edge to the underwing; Blue-billed Teal's upperwing is blackish with a glossy green speculum and crisp black and white borders.
4. Speculum details: Baikal Teal's green speculum has an indistinct cinnamon-cream inner border; Blue-billed Teal's speculum is glossy green, sharply bordered behind by black and white bars.
5. Breast spotting: Both species have spotted breasts, but Baikal Teal's spots are round and well-defined, while Blue-billed Teal's spots become vermiculated and less obvious on the flanks and underparts.
6. Adult male Baikal Teal (breeding): Unmistakable with a green nape, yellow and black face, and white bars on the sides. Blue-billed Teal male is much plainer, with a dark brown crown, pale face, and blackish ear patch.
7. Female/juvenile confusion: Female and juvenile Baikal Teal can be confused with Blue-billed Teal, but the Baikal's pale loral spot, white throat, and longer tail are key. Blue-billed Teal females are browner, with less contrast and no pale loral spot or white throat.
8. Juvenile marks: Juvenile Baikal Teal resembles the female but always shows the pale loral spot and white throat; juvenile Blue-billed Teal is duller and less spotted, lacking any pale face marks.
9. Bill color: Blue-billed Teal has a light bluish-grey bill with a blackish culmen and nail; Baikal Teal's bill is darker and less striking.
10. Size and structure: Baikal Teal is larger, bulkier, and longer-tailed; Blue-billed Teal is smaller, lighter, and daintier.
11. Habitat and range: Baikal Teal is found in East Asia (winter) and eastern Russia (breeding); Blue-billed Teal is strictly African/Malagasy. If seen outside these ranges, consider vagrancy or escape.
12. Flight jizz: Baikal Teal appears more robust and elongated in flight, with a longer tail projection; Blue-billed Teal is compact and short-tailed.
13. Scapulars and upperparts: Blue-billed Teal has dark brown to black scapulars and tail, with upperwing coverts showing a greenish gloss; Baikal Teal's upperparts are plainer except for the speculum.
14. Sexual dimorphism: Both species show some sexual dimorphism, but Baikal Teal's male is far more striking in breeding plumage. Female Blue-billed Teal is only subtly different from the male, mainly in crown color and less glossy wings.
15. Pitfall: Some Baikal Teal "females" with face bridle marks may be juvenile males; always check for the pale loral spot and white throat to avoid confusion.

Baikal Teal is noticeably larger and heavier (length 39–43 cm, height 30–40 cm, average weight ~500 g) than Blue-billed Teal (length 33–35 cm, weight 53–288 g). Baikal Teal is also longer-tailed and bulkier overall, while Blue-billed Teal is smaller, lighter, and more delicate in build. In direct comparison, Baikal Teal will look more robust and elongated, especially in the tail.

Juvenile and female Baikal Teal have a distinctive pale loral spot and white throat angled to the eye, plus a longer tail, which Blue-billed Teal lacks at all ages. Baikal Teal's underwing (all ages) has a darker leading edge and a green speculum with an indistinct cinnamon-cream inner border, while Blue-billed Teal's upperwing is blackish with a glossy green speculum, sharply bordered behind by black and white bars. Adult male Baikal Teal in breeding plumage is unmistakable with a green nape, yellow and black face, and white bars on the sides; Blue-billed Teal males have a dark brown crown, pale face, and a blackish patch on the ear region, with heavy black spotting on the neck and breast. Female Blue-billed Teal is browner, with less contrast in the face and less colorful wings. Juvenile Blue-billed Teal is duller and less spotted than adults, lacking any pale loral spot or white throat. Both species have spotted breasts, but the Baikal's are rounder and more defined, while Blue-billed Teal's spots become vermiculated on the underparts.

Both are dabbling ducks, but Baikal Teal tends to be more robust and may appear more upright due to its longer tail. Blue-billed Teal is daintier and often appears more delicate in posture. Blue-billed Teal's social and courtship behaviors are subtle and undemonstrative, with displays involving head turning and wing flapping, but these are not likely to aid field separation unless observed at close range.

Baikal Teal breeds in eastern Russia and winters in East Asia, while Blue-billed Teal is resident across sub-Saharan Africa and Madagascar. Their ranges do not overlap, so geographic context is usually a strong clue. Baikal Teal is migratory, often found in large flocks on East Asian wetlands in winter; Blue-billed Teal is more sedentary but can be nomadic in response to drought, frequenting small, vegetated wetlands.