カオグロアメリカムシクイ 対 クロズキンアメリカムシクイ

The most reliable field mark is the presence of a bold black facial mask in adult male Common Yellowthroat, versus the full black hood (including throat and crown) in adult male Hooded Warbler. Females and immatures of both species lack these strong black markings and are easily confused, but Hooded Warbler always shows a clean, unmarked yellow face with an olive-green cap, while Common Yellowthroat females and immatures have duller yellow underparts and a more uniform olive face. In flight, Hooded Warbler shows white outer tail feathers, a feature never present on Common Yellowthroat. Both are small, olive-backed warblers with yellow underparts, but subtle differences in face pattern, tail, and habitat use help separate them. Voice and behavior can also be useful, especially when plumage is ambiguous.

1. Adult male face pattern: Look for a black mask (across eyes and forehead, bordered above with white/gray) in Common Yellowthroat; look for a full black hood (surrounding the entire yellow face, including crown and throat) in Hooded Warbler. This is the most reliable mark for adult males.
2. Female and immature face: Female and immature Hooded Warbler shows a clear yellow face with an olive-green cap, which does not extend to the forehead, ears, or throat. Common Yellowthroat females and immatures have a more uniform olive face and paler yellow underparts, lacking any distinct cap.
3. First-year male Common Yellowthroat: May show a faint, partial black mask by spring, but never a full hood. Hooded Warbler males do not acquire the full hood until 9–12 months old, so young males resemble females.
4. White in tail: Hooded Warbler always shows white outer tail feathers (outer rectrices), visible in flight or when flicking the tail. Common Yellowthroat never shows white in the tail.
5. Underparts color: Hooded Warbler typically has brighter, more saturated yellow underparts; Common Yellowthroat is often duller, especially in females and immatures.
6. Back color: Both are olive-backed, but Hooded Warbler may appear slightly more greenish or brownish-olive. This is subtle and not always reliable.
7. Habitat: In marshes, reeds, or wet brushy areas, expect Common Yellowthroat. In mature, broadleaved forests with dense understory, expect Hooded Warbler.
8. Behavior: Hooded Warbler often flicks its tail to show white; Common Yellowthroat moves quickly and low, often remaining hidden in dense vegetation.
9. Song: Common Yellowthroat sings "twichety twichety twichety twich"; Hooded Warbler sings "wheeta wheeta whee-tee-oh" or similar. Learn these by ear for quick separation.
10. Call notes: Hooded Warbler gives a loud "chip"; Common Yellowthroat gives a soft "jip."
11. Geographic range: Hooded Warbler is restricted to eastern North America; Common Yellowthroat is widespread across the continent. In the west, a yellowthroat is almost always Common Yellowthroat.
12. Season: Both species are migratory in the north, but Common Yellowthroat is more likely to be found in winter in southern US and Mexico. Hooded Warbler winters farther south.
13. Bill and structure: No strong differences noted in the sources, but Hooded Warbler may appear slightly longer-tailed and more slender. Not usually diagnostic in the field.
14. Subspecies variation: Some Common Yellowthroat subspecies (especially in the southwest) are brighter yellow below, but never show a full black hood or white in the tail.
15. Pitfall: Immature and female Hooded Warbler can be confused with other yellow-faced warblers, but the combination of yellow face, olive-green cap, and white in tail is unique.

Hooded Warbler is slightly larger overall, measuring about 13 cm (5.1 in) in length and weighing 9–12 g, with a wingspan of 17.5 cm (6.9 in) [wikipedia]. Common Yellowthroat is somewhat smaller and more compact, but exact measurements are not provided in the notes. In the field, this size difference is subtle and not usually diagnostic unless both species are seen side by side.

• Juvenile/Immature birds: Both species' immatures and females lack the strong black markings of adult males, making them tricky to separate. However, Hooded Warbler immatures and females have a clear yellow face with an olive-green cap that does not extend to the forehead, ears, or throat, while Common Yellowthroat immatures and females have a more uniform olive face and paler yellow underparts. First-year male Common Yellowthroat may show a faint black mask, especially by spring, but never a full hood.
• Adult males: Common Yellowthroat males have a black mask across the eyes and forehead, bordered above with white or gray, and yellow throat and chest. Hooded Warbler males have a full black hood covering the crown, nape, and throat, with a bright yellow face and underparts. The black on Hooded Warbler is more extensive and surrounds the entire face, not just the eyes.
• Wings and Tail: Hooded Warbler shows white outer tail feathers (outer rectrices) in all plumages, especially visible in flight or when flicking the tail. Common Yellowthroat lacks any white in the tail.
• Back and Upperparts: Both species have olive backs, but Hooded Warbler's is sometimes described as more greenish or brownish-olive. This is subtle and not always reliable.

Both species forage low in dense vegetation, but Hooded Warbler is more likely to be seen flycatching or sallying from perches, often flicking its tail to reveal white outer feathers. Common Yellowthroat tends to skulk in marshes, reeds, or thick brush, moving quickly and often remaining hidden. Hooded Warbler is more likely to be seen in mature woodlands with dense undergrowth, while Common Yellowthroat prefers wetter, more open, or edge habitats.

Common Yellowthroat is abundant in marshes, wetlands, and brushy edges across much of North America, especially in areas with dense, low vegetation. Hooded Warbler breeds in broadleaved woodlands with dense undergrowth, mainly in the eastern US and southern Ontario. If you find a yellow warbler in a wet, open marsh, it's more likely a Common Yellowthroat; in a mature, shady forest with thick understory, Hooded Warbler is more likely.

Common Yellowthroat's song is a loud, repetitive "twichety twichety twichety twich," and its call is a soft "jip." Hooded Warbler's song is a series of musical notes, often rendered as "wheeta wheeta whee-tee-oh" (mnemonic: "The red, the red T-shirt" or "Come to the woods or you won't see me"), with a loud "chip" call. The songs are quite different, but both can be variable and may overlap in rhythm. Calls are more distinct, with Hooded Warbler's being sharper and louder.