ヨーロッパコシアカツバメ／アフリカコシアカツバメ／コシアカツバメ 対 コズアカコシアカツバメ

Juvenile and adult Red-rumped Swallows and Lesser Striped Swallows can look similar, especially in flight, but the most reliable field mark is the head and rump color: Lesser Striped Swallow shows a bright rufous-chestnut crown and nape with a deep red rump, while Red-rumped Swallow has a blue crown and nape and a paler, streaked or uniform chestnut rump depending on subspecies. Both have white underparts with dark streaks, but Lesser Striped Swallow's streaking is usually heavier and its head color stands out at a distance. Tail shape and length can help: Lesser Striped Swallow generally has longer, more deeply forked tail streamers, especially in males. Range is a strong clue—Red-rumped Swallow is Asian, Lesser Striped is African—but vagrants do occur. Juveniles of both are duller and browner, but the head and rump differences persist.

1. Head color is key: Lesser Striped Swallow always shows a bright rufous-chestnut crown, nape, and sides of the head. Red-rumped Swallow has a blue crown and nape, sometimes with a faint reddish collar, but never the full rufous head.
2. Rump color and pattern: Red-rumped Swallow's rump varies by subspecies—either uniform dark chestnut (C. d. erythropygia) or paler with dark shaft streaks (C. d. nipalensis). Lesser Striped Swallow has a deeper, richer red rump without streaks.
3. Underpart streaking: Both have white underparts with dark streaks, but Lesser Striped Swallow's streaking is heavier and more extensive, sometimes making the underparts look densely marked.
4. Tail shape and length: Lesser Striped Swallow has a more deeply forked tail with longer outer feathers, especially in males. Red-rumped Swallow's tail is deeply forked but can appear shallower, and the white patches on the tail are less distinct.
5. Juvenile differences: Juvenile Red-rumped Swallow is duller and browner with a paler rump and shorter tail, but still lacks the rufous-chestnut crown of Lesser Striped Swallow. Juvenile Lesser Striped Swallow is also duller but retains the rufous head.
6. Underwing coverts: Lesser Striped Swallow has tawny underwing coverts, which can be seen in good light or photos; Red-rumped Swallow does not.
7. Facial pattern: Lesser Striped Swallow's rufous head and nape contrast strongly with the dark blue back. Red-rumped Swallow's face is white with heavy dark streaking but lacks the rufous crown.
8. Flight jizz: Lesser Striped Swallow often appears bulkier and longer-tailed in flight, with a more erratic flight style. Red-rumped Swallow is more slender and has a smoother, more direct flight.
9. Perched jizz: When perched, Lesser Striped Swallow's longer tail streamers and rufous head are obvious. Red-rumped Swallow appears more compact and blue-headed.
10. Habitat and range: Use range as a strong clue—Red-rumped Swallow is Asian, Lesser Striped Swallow is African. Habitat overlap is rare except in vagrancy.
11. Nesting behavior: Lesser Striped Swallow often nests on buildings, bridges, or culverts; Red-rumped Swallow prefers natural sites and is less likely to use man-made structures.
12. Voice: If you hear a nasal 'zeh zeh zeh zeh zeh', it's Lesser Striped Swallow. Red-rumped Swallow's call is not distinctive in these notes.
13. Sex differences: Tail streamer length is slightly greater in male Lesser Striped Swallow, but not a primary field mark unless birds are side by side.
14. Subspecies confusion: Be aware of Red-rumped Swallow subspecies variation in rump color and tail fork depth; always check head color first.
15. Pitfalls: Both species can look similar in poor light or at a distance, especially juveniles. Focus on head and rump color, and use range and habitat context to support your ID.

Both species are similar in length, ranging from 15–19 cm, but Lesser Striped Swallow is described as 'large' for a swallow and often appears bulkier in the field. Red-rumped Swallow is typically more slender and slightly smaller overall, but size overlap is considerable and not always reliable for separation. Tail streamer length is slightly greater in Lesser Striped Swallow, especially in adult males, giving it a longer-tailed look when perched or in flight.

• Juveniles (both species): Both are duller and browner than adults, with shorter tail streamers. Red-rumped Swallow juveniles have a paler rump and less contrast overall, while Lesser Striped Swallow juveniles are also duller but retain the rufous-chestnut crown and nape, which Red-rumped Swallow lacks at all ages.
• Adults: Red-rumped Swallow has blue upperparts with a reddish (sometimes faint or absent) collar and a chestnut rump that may be streaked or uniform depending on subspecies. Lesser Striped Swallow has dark blue upperparts, a deep red rump, and a bright rufous-chestnut crown, nape, and sides of the head. Underparts in both are white with dark streaking, but Lesser Striped Swallow's streaking is heavier and more extensive. The underwing coverts of Lesser Striped Swallow are tawny, while Red-rumped Swallow's are not described as such. Tail: Lesser Striped Swallow's tail is more deeply forked and blackish with very long outer feathers; Red-rumped Swallow's is deeply forked but can appear shallower in some subspecies, and the white patches on the tail are less distinct.

Both species are aerial insectivores, often seen flying low over open areas. Lesser Striped Swallow's flight is described as erratic, and it frequently uses man-made structures for nesting, sometimes high up. Red-rumped Swallow is more associated with open, hilly country and clearings, and is less likely to be found nesting on buildings. Both perch on wires, but Lesser Striped Swallow may appear bulkier and longer-tailed when perched.

Red-rumped Swallow is found in open, often hilly areas with clearings and cultivation across eastern and southeastern Asia to northeastern India and Taiwan. Lesser Striped Swallow is endemic to Sub-Saharan Africa, breeding from Sierra Leone and southern Sudan south to eastern South Africa, and is more likely to be seen near human habitation due to its nesting preferences. Range is a strong separator: Red-rumped Swallow is Asian, Lesser Striped Swallow is African, with only rare vagrancy outside these regions.

Lesser Striped Swallow gives a nasal 'zeh zeh zeh zeh zeh' call. No distinctive vocalization is described for Red-rumped Swallow in these notes, so voice is only useful if Lesser Striped Swallow's call is heard.