キマユヒヨドリ 対 ミヤマヒヨドリ

The most reliable field mark to separate Yellow-browed Bulbul from Mountain Bulbul is the presence of a bright, well-defined yellow eyebrow and all-yellow underparts in Yellow-browed Bulbul, versus the more muted, streaked, or rufous-tinged underparts and lack of a strong yellow brow in Mountain Bulbul. Both species are forest bulbuls, but Yellow-browed Bulbul is strictly olive above and yellow below, with a distinctive facial pattern, while Mountain Bulbul is generally duller, sometimes with greenish wings and a rufous or streaked belly. Structure is similar, but Yellow-browed Bulbul lacks a crest and has a more uniform, clean look. Habitat and range do not overlap: Yellow-browed is found in southern India and Sri Lanka, Mountain Bulbul in Southeast Asia.

1. Yellow brow and facial pattern: Yellow-browed Bulbul always shows a bright yellow eyebrow and yellow orbital area ('goggles'), making the face look open and bright. Mountain Bulbul lacks this feature; its face is plainer and less contrasting.
2. Underparts color: Yellow-browed Bulbul is uniformly bright yellow below (with minor greenish or bronzy tinges in some subspecies), while Mountain Bulbul has duller, streaked, or rufous-tinged underparts. Look for clean, unmarked yellow in Yellow-browed.
3. Upperparts: Both are olive or greenish above, but Yellow-browed is more uniform and clean, while Mountain Bulbul may look duller or more streaked.
4. Crest: Yellow-browed Bulbul lacks a crest, giving it a smooth, rounded head profile. Mountain Bulbul sometimes shows a slight crest or raised crown feathers, but this is not always obvious.
5. Bill and iris: Yellow-browed Bulbul has a black bill and reddish-brown iris, but these are subtle marks and not always visible in the field.
6. Subspecies variation: If in the northern Western Ghats, Yellow-browed Bulbul may appear paler yellow (A. i. icterica), but still shows the yellow brow. In Sri Lanka, southwestern birds may look greener below, but the yellow brow remains diagnostic.
7. No strong age/sex differences: Both species have similar plumage across sexes and ages, so these marks are reliable year-round.
8. No distinctive wing or flight pattern: Neither species shows unique upperwing or flight marks in any age, so focus on perched birds and facial/underpart color.
9. Habitat and range: If seen in southern India or Sri Lanka, especially in forest, a yellow-browed bulbul is almost certainly Yellow-browed Bulbul. In Southeast Asia, Mountain Bulbul is the likely candidate.
10. Group behavior: Both species may join mixed flocks, but this is not a separator.
11. Alternate names can confuse: Mountain Bulbul's alternate names (e.g., 'green-winged', 'rufous-bellied', 'streaked') reflect its more variable, streaked, or rufous-tinged plumage—never clean yellow below.
12. Plumage pitfalls: Do not confuse the greenish or olive upperparts of both species; focus on the underparts and face for separation.
13. No strong vocal differences described: Use visual marks primarily for separation.
14. Size is not a reliable field mark: Both are similar in length and bulk; use color and pattern instead.
15. If in doubt, check for the yellow brow: This is the single most reliable mark for Yellow-browed Bulbul in all ages and seasons.

Mountain Bulbul is slightly heavier, with an average adult mass of 33 g [wikidata]. No direct mass data is available for Yellow-browed Bulbul, but both are medium-sized bulbuls (Yellow-browed about 20 cm in length [wikipedia]). In the field, size is not a strong separator, as both are similar in overall proportions and bulk.

No age-specific wing or flight pattern differences are described for either species, so separation relies on overall plumage and facial pattern in all ages. Yellow-browed Bulbul of all ages and sexes is olive-green above and bright yellow below, with a prominent yellow brow and yellow 'goggles' around the eye, and no crest. Subspecies vary slightly: northern Western Ghats birds are paler, southern birds brighter, and Sri Lankan birds sometimes show a greenish tinge below. Mountain Bulbul, in contrast, lacks a strong yellow brow; its plumage is generally dull olive or greenish above, with underparts that can be streaked or rufous-tinged (hence alternate names like 'rufous-bellied bulbul' and 'mountain streaked bulbul'). The face is less marked, and the overall look is more muted and streaky, without the clean, bright yellow of Yellow-browed Bulbul.

Both species are typical bulbuls in behavior, foraging in the mid to upper canopy and moving in small groups. Yellow-browed Bulbul is often seen in pairs or small parties, sometimes joining mixed flocks. No distinctive behavioral differences are noted in the sources that would reliably separate these two species in the field.

Yellow-browed Bulbul is restricted to forests of southern India and Sri Lanka, especially in the Western Ghats, Nilgiris, and Sri Lankan wet zone [wikipedia]. Mountain Bulbul is found in Southeast Asia, typically in hill and montane forests. There is no range overlap, so location is a strong clue: any bulbul with a yellow brow in southern India or Sri Lanka is almost certainly Yellow-browed, while similar birds in Southeast Asian mountains are Mountain Bulbul.