シコンヒワ 対 ニカラグアオオコメワリ

The most reliable field mark to separate Blue-black Grassquit from Nicaraguan Seed-Finch is bill size and shape: the seed-finch has a massive, deep-based, pale (ivory or pinkish) bill, while the grassquit’s bill is much slimmer and conical. In flight, female and juvenile grassquits show faint wingbars and a streaked breast, unlike the plainer, darker brown female/juvenile seed-finch. Males of both species are black, but the grassquit male is smaller, with a blue sheen and a subtle white underwing flash in flight, while the seed-finch male is bulkier, lacks blue gloss, and has a strikingly pale bill. Size and structure are also useful: the seed-finch is much larger and heavier-bodied. Both species can occur in similar weedy fields, but the seed-finch is more restricted in range and habitat.

1. Bill size and color: Nicaraguan Seed-Finch has a massive, deep-based, pale (ivory or pinkish) bill in males, and a blackish bill with a pale base in females. Blue-black Grassquit has a much slimmer, sharply conical, dark bill. This is the single most reliable field mark at any age or sex.
2. Overall size and shape: Seed-finch is nearly twice the weight and much longer than grassquit. In the field, the seed-finch looks bulky and heavy-headed, while the grassquit is petite and sparrow-like.
3. Male plumage: Adult male grassquit is glossy blue-black with a small white underwing patch (sometimes visible in flight), and a slim dark bill. Male seed-finch is matte black (no blue gloss), with a huge, pale bill and no white in the wing. The grassquit male is much smaller and more active.
4. Female/juvenile plumage: Female/juvenile grassquits are warm brown with faint streaks, two subtle wingbars, and a streaked breast and flanks. Female/juvenile seed-finches are darker brown, lack wingbars, and have plainer, sometimes cinnamon underparts with little or no streaking. The seed-finch's bill is always deeper and paler at the base.
5. Wingbars: Only grassquit females/juveniles show faint wingbars (from pale tips to coverts); seed-finch never shows wingbars at any age.
6. Underwing/flight marks: Grassquit (especially nominate and peruviensis) shows a white patch at the base of the underwing (axillaries and underwing coverts) in flight, especially in males. Seed-finch has uniformly dark underwings.
7. Tail: Grassquit has a brown tail with buff tips on outer feathers (in fresh plumage), which wear off quickly. Seed-finch has a plain dark tail, matching the rest of the plumage.
8. Breast streaking: Grassquit females/juveniles have a band of dark streaks across the breast and along the flanks; seed-finch females/juveniles are much plainer below.
9. Leg color: Both species have dark legs, not useful for separation.
10. Iris color: Both species have brown irises, not diagnostic.
11. Display behavior: Grassquit males often perform bouncing display flights from exposed perches; seed-finch does not.
12. Habitat and range: Grassquit is widespread and common in open, weedy, or grassy habitats throughout the Neotropics. Seed-finch is restricted to Costa Rica, Nicaragua, and Panama, and prefers wetter, marshy areas.
13. Jizz: Grassquit is quick, active, and often perches on grass stems or wires. Seed-finch is slower, heavier, and more likely to be found low in dense vegetation.
14. Voice: Not described in the provided notes; do not rely on vocalizations for separation with current information.
15. Pitfalls: Immature grassquits can be confused with seed-finches if bill size is not carefully noted, especially if wingbars are worn or faint. Always check bill depth and color, and look for subtle streaking or wingbars in grassquits.

Blue-black Grassquit is much smaller (8.7–10.9 cm, 8–12 g) than Nicaraguan Seed-Finch (14–14.5 cm, ~24 g) [wikipedia]. The seed-finch is nearly twice as heavy and noticeably longer, with a much more robust body and a disproportionately large bill. Side-by-side, the grassquit looks dainty and sparrow-like, while the seed-finch is chunky and bull-headed.

• Juvenile/immature/female contrast: Female and juvenile Blue-black Grassquits are warm brown above with faint streaks and two subtle wingbars, plus a streaked breast and flanks. Their wings and tail are brown with paler tips (outer tail feathers may show buff tips when fresh). Juvenile/female Nicaraguan Seed-Finches are darker brown above, lack wingbars, and have plainer, sometimes cinnamon-brown underparts without strong streaking. The seed-finch's bill is always much deeper and paler at the base (females: blackish with pinkish ivory base).

• Adult male contrast: Male Blue-black Grassquit is glossy blue-black with a slim, dark bill and a small white patch at the base of the underwing (visible in flight). Male Nicaraguan Seed-Finch is entirely black (no blue gloss) with a huge, pale ivory or pink bill and no white in the wing. Grassquit males are much smaller and more delicate in build.

• Flight marks: Grassquit females/juveniles may show faint wingbars and a pale underwing patch (especially in nominate and peruviensis subspecies), while seed-finch shows uniform dark wings with no pale patches or wingbars.

Blue-black Grassquit is often seen making short, bouncing display flights from exposed perches, especially males. They are active, sometimes in small flocks, and frequently perch on grass stems or wires. Nicaraguan Seed-Finch is more deliberate and heavy in movement, often foraging low in dense vegetation or at the edge of marshes. The seed-finch rarely performs the acrobatic display flights typical of grassquits and is less likely to be seen in open, weedy fields far from water.

Blue-black Grassquit is widespread and adaptable, found in shrubby fields, grassy areas, roadsides, pastures, and open thickets from Mexico through most of South America, including islands [wikipedia]. Nicaraguan Seed-Finch is much more localized, restricted to Costa Rica, Nicaragua, and Panama, and tends to favor wetter habitats such as marsh edges, rank grass near water, and wet pastures. While both may occur in weedy fields, the seed-finch is less likely in dry or upland sites.