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The most reliable field mark between Pink-necked Green-Pigeon and Ashy-headed Green-Pigeon is the male Pink-necked's distinctive pinkish neck and orange breast, which Ashy-headed never shows. In flight, Pink-necked also shows a yellow bar across the wing (from yellow-edged tertials), visible in both sexes and especially in juveniles and females, while Ashy-headed lacks this feature. Females and immatures of both species are green overall and can be confusing, but Pink-necked is generally brighter below and shows a yellowish belly, while Ashy-headed is duller. Both are medium-sized green pigeons, but Pink-necked is slightly larger and more likely in lowland, open, or urban habitats, while Ashy-headed is more restricted to forested areas further north and west in Asia.

1. Male Pink-necked: pink neck and orange breast – Only male Pink-necked Green-Pigeon shows a pinkish neck and orange breast with a grey head; Ashy-headed males never show this, remaining green with an ashy (greyish) head.
2. Yellow wing bar in flight (all ages, both sexes, especially juveniles/females): Pink-necked shows a distinct yellow bar across the wing (from yellow-edged tertials) in flight or when wings are partially open. Ashy-headed lacks this yellow bar, so any green pigeon with a yellow wing bar is Pink-necked.
3. Belly and underparts (females/immatures): Female and juvenile Pink-necked are brighter below, with a yellowish belly and throat, while Ashy-headed is duller green and lacks strong yellow tones.
4. Tail pattern: Pink-necked has a grey tail with a black terminal band and chestnut uppertail coverts; look for this contrast when perched. Ashy-headed's tail is less contrasting.
5. Head color (females/immatures): Pink-necked females have a greenish crown and nape, blending into the yellowish face and throat. Ashy-headed females are more uniformly dull green, with an ashy tinge to the head.
6. Size: Pink-necked is slightly larger and heavier, but this is subtle and not usually diagnostic unless both species are side by side.
7. Habitat: Pink-necked is much more likely in open, lowland, or urban habitats (gardens, parks, plantations, mangroves), while Ashy-headed prefers forest or forest edge, especially in hilly or foothill regions.
8. Geographic range: If in the Philippines, Indonesia, or southern Malaysia/Singapore, it's Pink-necked. Ashy-headed is found further north and west (Nepal, NE India, Bangladesh, SW China, Myanmar, Thailand, Laos, Vietnam). Overlap is possible in Thailand and Vietnam, so use plumage and habitat.
9. Group size: Pink-necked often forms larger flocks, especially at fruiting trees or roosts; Ashy-headed is usually solitary or in small groups.
10. Behavior: Both species feed on fruit and seeds and have fast, direct flight, but Pink-necked is more conspicuous and tolerant of human presence.
11. Voice: Not reliable for separation; both are generally quiet, with Pink-necked sometimes giving a soft whistling call or 'krrak krrak' at communal roosts.
12. Sexual dimorphism: Only Pink-necked shows strong sexual dimorphism (male with pink neck/orange breast); Ashy-headed sexes are similar.
13. Juvenile confusion: Immature Pink-necked resembles adult female but is greyer above; Ashy-headed immature is dull green overall. The yellow wing bar in flight is still a good separator.
14. Leg and bill color: Pink-necked has pink or reddish legs and a pale bill (white, blue-green, or grey); Ashy-headed's leg and bill color is not described but is not a primary field mark.
15. When in doubt: If you see a green pigeon with a yellow wing bar or a male with a pink neck and orange breast, it's Pink-necked. If the bird is dull green with an ashy head and no yellow wing bar, especially in forested habitat north of the Malay Peninsula, it's likely Ashy-headed.

Pink-necked Green-Pigeon is slightly larger, measuring 25–30 cm in length and weighing 105–160 g [wikipedia]. Ashy-headed Green-Pigeon is similar in structure but is generally a bit smaller and slimmer, though exact measurements are not provided in the notes. In the field, size difference is subtle and often not reliable unless both are seen together.

• Juvenile and female contrast: Both species are green overall, but Pink-necked females and juveniles are brighter, with a yellowish belly and throat, and a greenish crown and nape. Ashy-headed females and immatures are duller green and lack the strong yellow tones below.
• Male contrast: Only male Pink-necked shows a pinkish neck and orange breast, with a grey head. Ashy-headed males do not show these colors and remain more uniformly green with an ashy (greyish) head.
• Wing pattern in flight (all ages): Pink-necked shows a yellow bar across the wing (from yellow-edged tertials), visible in flight in both sexes and juveniles. Ashy-headed lacks this yellow wing bar, making this a key field mark when birds are flying or perched with wings partially open.
• Tail: Pink-necked has a grey tail with a black terminal band and chestnut uppertail coverts, which can be visible when perched. Ashy-headed's tail pattern is not described in detail, but lacks the strong contrast of Pink-necked.

Both species feed on fruit and seeds and have a fast, direct flight typical of Treron pigeons. Pink-necked is often seen in larger, more conspicuous flocks, especially at fruiting trees or communal roosts, and is more likely to be found in open or urban settings. Ashy-headed is usually solitary or in small groups and tends to be more secretive, preferring denser forest or forest edge.

Pink-necked Green-Pigeon is widespread and common in Southeast Asia, favoring lowland areas, forest edge, mangroves, gardens, plantations, and even urban parks. It is especially likely in open or human-modified habitats. Ashy-headed Green-Pigeon is found further north and west (Nepal, NE India, Bangladesh, SW China, Myanmar, Thailand, Laos, Vietnam) and is more restricted to forested areas, often in hill or foothill forests. Overlap is possible in Thailand and Vietnam, but habitat preference can help: Pink-necked in open/urban, Ashy-headed in forest.

Both species are generally quiet. Pink-necked Green-Pigeon is not very vocal, but males may give a tri-syllabic whistling call ending in a coo, and a rasping 'krrak krrak' at times, mostly at communal roosts or when finding food. No distinctive vocalization is described for Ashy-headed in the notes, but Treron pigeons typically have soft, whistling or quacking calls rather than classic pigeon coos. Voice is not a reliable separator in the field.