ハシブトスミレフウキンチョウ 対 ホシスミレフウキンチョウ

The most reliable field mark between Thick-billed and Spot-crowned Euphonias is the male's forehead: Spot-crowned has a yellow patch speckled with black, while Thick-billed's is pure yellow. Females are trickier, but Spot-crowned shows a rufous-chestnut forehead and tawny-rufous belly, unlike the greenish-yellow, more uniform female Thick-billed. Both are small, similar-sized euphonias, but the bill of Thick-billed is noticeably heavier. In flight or perched, focus on the head and underpart color contrasts, especially in females. Range can help: Spot-crowned is restricted to Costa Rica and Panama, while Thick-billed is widespread through Central and northern South America.

1. Male forehead pattern: Spot-crowned Euphonia males have a yellow forehead patch speckled with black, extending to the rear of the eye; Thick-billed males have a pure yellow forehead patch that extends only slightly past the eye. This is the single most reliable field mark for adult males.
2. Male throat and chest: Spot-crowned males have blue-black throat and chest, with yellow only on the lower underparts; Thick-billed males have a yellow throat and underparts. This contrast is especially useful from a frontal view.
3. Female forehead and underparts: Female Spot-crowned has a rufous-chestnut forehead and a tawny-rufous belly and undertail coverts, while Thick-billed female is more uniformly yellowish olive-green above and greenish yellow below, with no rufous tones.
4. Bill structure: Thick-billed Euphonia has a noticeably thicker, heavier bill than Spot-crowned, though this can be subtle unless seen side-by-side or at close range.
5. Upperparts in females: Spot-crowned female shows a grayish-blue tinge to the dark olive-green crown and nape, while Thick-billed female is more plain olive-green above.
6. Tail and wing color: Both species have dusky wings and tails with blue-black tinges, but Spot-crowned male may show white bases on the inner webs of most flight feathers (not described for Thick-billed), though this is subtle and rarely diagnostic in the field.
7. Underpart color in females: Spot-crowned female's underparts are divided—olive-yellow on the throat, but the center of the lower breast, belly, and undertail coverts are tawny-rufous. Thick-billed female is greenish yellow below, palest on the undertail, with no rufous.
8. Range: Spot-crowned is only found in Costa Rica and Panama; Thick-billed ranges from Costa Rica south through much of northern South America. If you are outside Costa Rica or Panama, Spot-crowned is extremely unlikely.
9. Habitat overlap: Both can occur in semi-open habitats, forest edges, and gardens, so habitat alone is not diagnostic within the shared range.
10. Sexual dimorphism: Both species are sexually dimorphic, so always consider sex when comparing field marks.
11. No distinctive juvenile/immature wing pattern: There are no described age-specific wing or flight marks for either species, so rely on head and underpart color for all ages.
12. Bill color: Both have a blackish bill with a blue-gray base, so bill color is not a separator—focus on bill thickness.
13. Iris and leg color: Both have dark brown irises and dark gray legs/feet, not useful for separation.
14. Plumage variation: Some subspecies of Thick-billed show slight variation in yellow extent or undertail pattern, but none overlap with the Spot-crowned's unique male forehead speckling or female rufous tones.
15. Pitfall—female confusion: Female euphonias are often misidentified. Always check for the rufous-chestnut forehead and tawny-rufous belly in Spot-crowned female; absence of these points to Thick-billed.

Both species are nearly identical in length (about 10 cm) and mass (Thick-billed: 15 g, Spot-crowned: 14 g) [wikidata]. In hand or with excellent views, Thick-billed Euphonia has a slightly bulkier, thicker bill, but overall body size is not a reliable separator in the field.

No distinctive juvenile or immature wing patterns are described for either species, so adult plumage is the main field cue.

Adult males: Thick-billed Euphonia males have a bright yellow forehead (pure, not speckled), with the yellow patch extending just past the eye; the rest of the crown and upperparts are glossy blue-black, and the throat and underparts are bright yellow. Spot-crowned Euphonia males have a yellow forehead patch that extends further back and is distinctly speckled with black. Their blue-black upperparts are similar, but the throat and chest are also blue-black, with yellow only on the lower underparts.

Adult females: Thick-billed females are yellowish olive-green above and greenish yellow below, with the palest color on the undertail coverts. Spot-crowned females have a rufous-chestnut forehead, dark olive-green crown/nape with a grayish-blue tinge, and a tawny-rufous center to the lower breast, belly, and undertail coverts—this rufous wash is absent in Thick-billed.

In both sexes, the bill is blackish with a blue-gray base, but Thick-billed's is stouter. No seasonal or age-specific wing pattern differences are noted.

No distinctive behavioral differences are described between these two species. Both are typical euphonias, often seen in pairs or small groups, foraging for fruit in semi-open habitats and edges.

Thick-billed Euphonia is widespread, found in a broad range of open and semi-open habitats from southern Central America through much of northern South America, including forest edges, clearings, gardens, and cultivated areas. Spot-crowned Euphonia is much more restricted, found only in Costa Rica and Panama, and typically in similar semi-open or edge habitats. If you are outside Costa Rica or Panama, Spot-crowned is highly unlikely.