エジプトガン 対 アカツクシガモ

The most reliable field separation between Egyptian Goose and Ruddy Shelduck is the upperwing pattern in flight: both show prominent white wing coverts, but in Egyptian Goose the white is extensive and can be flashed in display, while in Ruddy Shelduck the white is sharply set off against black flight feathers and tail, especially visible in flight. Perched birds are more challenging, but Egyptian Goose is bulkier and variable in overall tone, while Ruddy Shelduck is more uniformly orange-brown with a paler head. Juveniles of both species resemble females but differ in tone and head pattern. Voice and jizz also help: Egyptian Goose is heavier and more goose-like in flight, while Ruddy Shelduck is sleeker and gives a loud, nasal honking.

1. Upperwing pattern in flight: Both show a large white panel on the upperwing, but in Egyptian Goose the white is extensive and can be flashed in display, while in Ruddy Shelduck the white is sharply bordered by black flight feathers and tail, with an iridescent green speculum visible at certain angles. This is most reliable in flight for both adults and immatures.
2. At rest: The white wing panel is mostly hidden in both, but Egyptian Goose may flash it when alarmed or aggressive. Ruddy Shelduck's white is less likely to be seen unless the wings are spread.
3. Body shape and jizz: Egyptian Goose is bulkier, with a heavy, goose-like build and ponderous flight. Ruddy Shelduck is slimmer, more duck-like, and appears lighter on the water and in the air.
4. Head pattern: Egyptian Goose always shows a dark brown eye patch and a chest band, regardless of age or sex. Ruddy Shelduck has a pale orange or whitish head (especially in females and juveniles) and lacks any eye patch or chest band.
5. Plumage tone: Egyptian Goose is variable, ranging from greyish to brownish, with no consistent age or sex differences. Ruddy Shelduck is more uniform orange-brown, with a paler head and (in males) a narrow black neck collar during the breeding season.
6. Tail and flight feathers: Ruddy Shelduck has black tail and flight feathers, contrasting sharply with the white wing coverts. Egyptian Goose's tail is less contrasting and blends more with the body plumage.
7. Juvenile birds: Ruddy Shelduck juveniles are darker brown with a pale, whitish head, similar to the adult female but lacking the black neck collar. Egyptian Goose juveniles resemble adults and are not reliably separable by plumage tone alone.
8. Voice: Egyptian Goose males give a hoarse, subdued quack or breathy, rapid calls; females are much noisier and raucous. Ruddy Shelduck gives loud, nasal honking notes, more resonant and less harsh than Egyptian Goose's quacks. Listen for these differences, especially in flight or when birds are alarmed.
9. Behavior: Egyptian Goose is often seen displaying or being aggressive, flashing its white wing patches and chasing intruders. Ruddy Shelduck is less likely to display in this way and is generally less aggressive in mixed flocks.
10. Habitat context: In Europe, Egyptian Goose is more likely in ornamental lakes, parkland, and urban water bodies, while Ruddy Shelduck prefers larger, open water bodies and is generally scarcer.
11. Sex differences: Ruddy Shelduck males have a narrow black neck collar in breeding plumage, lost in eclipse and absent in females/juveniles. Egyptian Goose shows no sex differences in plumage, only in size (males larger).
12. Seasonal changes: Ruddy Shelduck males lose the black collar after breeding and regain it in a partial moult December–April; otherwise, plumage is similar year-round. Egyptian Goose shows no seasonal plumage change.
13. Bill and legs: Both have dark bills and legs, not a useful field mark for separation.
14. Size in mixed flocks: If seen together, Egyptian Goose is noticeably larger and bulkier than Ruddy Shelduck, but beware overlap in lone birds.
15. Common pitfalls: Beware that both can appear variable in tone and that the white wing panel is often hidden at rest. Always try to observe birds in flight or when displaying for the most reliable separation.

Egyptian Goose is the heavier and slightly longer of the two, typically 63–73 cm in length and weighing 1,500–2,348 g (no AVONET mass available) [wikipedia]. Ruddy Shelduck is smaller, at 58–70 cm in length and 1,230 g (adult) [wikidata]. Both are large waterfowl, but Egyptian Goose is distinctly bulkier and more goose-like in build, while Ruddy Shelduck is a bit slimmer and more duck-like in proportions.

• Juvenile/immature birds: Both species' juveniles resemble their respective females, but Ruddy Shelduck juveniles are a darker brown overall and have a pale, whitish head, while Egyptian Goose juveniles are not described as differing markedly from adults, and plumage variation is not age-related [wikipedia].
• Upperwing in flight (all ages): Both species show a large white panel on the upperwing, but in Egyptian Goose the white is extensive and can be flashed in display, while in Ruddy Shelduck the white is sharply set off against black flight feathers and tail, with an iridescent green speculum on the inner wing [wikipedia]. At rest, the white is mostly hidden in both, but can be revealed when the bird is alert or aggressive (Egyptian Goose) or in flight (both).
• Adult body plumage: Egyptian Goose is highly variable in tone (greyer or browner), with a dark eye patch and chest band, while Ruddy Shelduck is more uniform orange-brown with a paler head and, in males, a narrow black neck collar (lost in eclipse plumage and absent in females/juveniles). Ruddy Shelduck's tail and flight feathers are black, contrasting with the white wing coverts.
• Head pattern: Egyptian Goose has a dark brown patch around the eye and a chest band, while Ruddy Shelduck has a pale orange or whitish head (females/juveniles paler than males) and no eye patch.

Egyptian Goose appears heavy and goose-like in flight, with deep wingbeats and a tendency to display its white wing patches when alarmed or aggressive. It is highly territorial, often chasing intruders in aerial 'dogfights.' Ruddy Shelduck is sleeker in flight, with a more duck-like jizz and less ponderous movements. Both species are aggressive when breeding, but Egyptian Goose is especially noted for territoriality and aerial pursuits.

Egyptian Goose is often found in parkland, lakes, and rivers, especially where there are mature trees for nesting. It has expanded its range in Europe and is often seen in ornamental or semi-wild settings. Ruddy Shelduck prefers large inland water bodies such as lakes, reservoirs, and rivers, often in more open landscapes, and may nest well away from water in cliffs or trees. In Europe, Ruddy Shelduck is generally scarcer and more localized than Egyptian Goose, which is now widespread in some regions.

Both species are vocal, but their calls differ. Egyptian Goose males give a hoarse, subdued quack or a breathy, rapid call (like a steam engine), while females are much noisier, with a raucous, aggressive quack. Ruddy Shelduck gives loud, nasal honking notes, with male and female calls distinguishable but both much more honking and less quacking than Egyptian Goose. Ruddy Shelduck calls are given both on the ground and in flight and are generally more resonant and less harsh than the Egyptian Goose's aggressive quacks.