コシグロクサシギ 対 コキアシシギ

The most reliable way to separate Solitary Sandpiper from Lesser Yellowlegs is by their rump and tail pattern in flight: Solitary Sandpiper shows a dark rump and tail center, while Lesser Yellowlegs has a plain, unmarked rump and tail. On the ground, Solitary Sandpiper is smaller and more compact, with a shorter, straight bill and greenish legs (not yellow). Lesser Yellowlegs is noticeably larger, with long, bright yellow legs and a slimmer, more elongated look. Both species can show streaked breasts and white underparts, but their structure and flight patterns are distinct. Always check rump and tail in flight, and leg color and proportions when perched.

1. Rump and tail pattern in flight: Solitary Sandpiper always shows a dark rump and tail center, while Lesser Yellowlegs has a plain, pale rump and tail. This is the single most reliable mark for any age or season.
2. Leg color: Solitary Sandpiper has greenish legs; Lesser Yellowlegs has bright yellow legs. This is obvious in good light but can be tricky in muddy water or poor light.
3. Size and structure: Solitary Sandpiper is smaller, dumpier, and shorter-legged. Lesser Yellowlegs is taller, longer-necked, and more slender, with a proportionally longer bill and legs.
4. Bill shape and length: Both have straight, dark bills, but Lesser Yellowlegs' bill is longer relative to its head, while Solitary Sandpiper's is shorter and stubbier.
5. Upperpart pattern: Solitary Sandpiper has a dark greenish back with fine light spots; Lesser Yellowlegs is more mottled in breeding plumage and plainer grey-brown in non-breeding.
6. Breast markings: Both show streaked breasts, but Lesser Yellowlegs' streaks are finer and more extensive, especially in breeding plumage.
7. Flight style: Solitary Sandpiper is compact and direct in flight; Lesser Yellowlegs is more elongated and graceful, with longer wings.
8. Foraging behavior: Lesser Yellowlegs is more active, moving quickly and often in small groups; Solitary Sandpiper is more solitary and deliberate.
9. Habitat preference: Solitary Sandpiper favors wooded ponds and shaded pools, often alone. Lesser Yellowlegs prefers open wetlands and is more likely to be seen in groups.
10. Vocalizations: Listen for Solitary Sandpiper's sharp three-note whistle, especially when flushed. Lesser Yellowlegs' call is softer and less distinctive.
11. Tail-bobbing: Solitary Sandpiper bobs its tail more frequently and noticeably than Lesser Yellowlegs.
12. Seasonal confusion: In non-breeding plumage, Lesser Yellowlegs becomes plainer above, making leg color and rump pattern even more important.
13. Pitfalls: Muddy legs, poor light, or distance can obscure leg color; always try to see the bird in flight for rump pattern. Juvenile and adult Lesser Yellowlegs can look similar to Solitary Sandpiper on the ground, so use multiple marks.
14. Group size: Solitary Sandpiper is almost always alone; Lesser Yellowlegs is often in small flocks, especially on migration.
15. Context: If you see a Tringa sandpiper in a shaded, wooded pond, especially alone, suspect Solitary Sandpiper—but confirm with rump and leg color.

Solitary Sandpiper is significantly smaller and more compact, with an average body mass of about 49 g, compared to the much heavier Lesser Yellowlegs at 81 g [wikidata]. Solitary Sandpiper measures 18–23 cm in length with a wingspan up to 50 cm, while Lesser Yellowlegs is 23–25 cm long with a wingspan of 59–64 cm [wikipedia]. In the field, Lesser Yellowlegs stands taller on its long legs and appears more slender, while Solitary Sandpiper looks dumpier and shorter-legged.

For all ages, the most diagnostic plumage difference is seen in flight: Solitary Sandpiper shows a dark rump and tail center, which sharply contrasts with the white rump and tail of Lesser Yellowlegs (though the latter's tail is not as brilliant white as Green Sandpiper, it is still unmarked and pale). On the ground, Solitary Sandpiper has a dark greenish back, greyish head and breast, and white underparts, with fine light spotting on the wings. Lesser Yellowlegs in breeding plumage has more extensive mottling on the upperparts (grey-brown, black, and white), with a white belly and irregular brown streaking on the breast and neck; in non-breeding plumage, the upperparts are plainer grey-brown. Both species have streaked breasts, but Lesser Yellowlegs often shows finer and denser markings. Leg color is a strong mark: Solitary Sandpiper has greenish legs, while Lesser Yellowlegs has bright yellow legs. Bill color is also useful: Solitary Sandpiper's bill is straight and dark, while Lesser Yellowlegs' is also straight and dark but appears longer relative to head size.

Lesser Yellowlegs is very active when foraging, often moving quickly with a high-stepping gait and neck outstretched. Solitary Sandpiper is more deliberate, often feeding alone and showing a dumpier, more reserved posture. Both species may bob their tails, but Solitary Sandpiper does so more frequently and noticeably. In flight, Lesser Yellowlegs appears longer-winged and more graceful, while Solitary Sandpiper is more compact and direct.

Both species can be found in freshwater habitats during migration, but Solitary Sandpiper is more likely to be seen alone along wooded ponds, small streams, and shaded pools, often away from open mudflats. Lesser Yellowlegs prefers open, shallow wetlands, flooded fields, and marshes, often in small groups. During breeding, Solitary Sandpiper nests in trees (unusual for shorebirds), while Lesser Yellowlegs nests on the ground in boreal forest wetlands.

Solitary Sandpiper gives a distinctive three-note whistle in flight, which is sharper and more abrupt than the softer, less emphatic calls of Lesser Yellowlegs. Lesser Yellowlegs' calls are generally softer and less piercing than those of Greater Yellowlegs, but not as sharp or distinctive as Solitary Sandpiper.