ハシビロガモ 対 ヒドリガモ

The most reliable way to separate Northern Shoveler from Eurasian Wigeon in the field is by bill shape: shovelers have a huge, spatulate bill, while wigeons have a normal duck bill. In flight, both species show pale forewings, but the shoveler’s is blue and the wigeon’s is brilliant white. Female and eclipse-plumaged shovelers can be confused with female wigeons, but the shoveler’s bill remains distinctive at all ages and sexes. Males in breeding plumage are easily told apart by head color and pattern. Immature and eclipse birds are trickier, but wing pattern and bill shape remain reliable. Both are dabbling ducks, but their feeding behavior and flocking tendencies differ.

1. Bill shape is the single most reliable mark: Northern Shoveler has a huge, broad, spatulate bill at all ages and sexes; Eurasian Wigeon has a normal, gently sloping duck bill. If you can see the bill well, this is diagnostic.
2. In flight, check the forewing color: Shoveler (all ages/sexes) shows a pale blue (male) or grey (female) forewing, separated from a green speculum by a white border; Wigeon (all ages/sexes) shows a brilliant white upperwing patch and a dark green speculum. This is especially useful for females and immatures.
3. Breeding male head pattern: Shoveler drake has a dark green (often looks black at distance) head and white breast; Wigeon drake has a chestnut head with a creamy crown and pink breast. These are obvious at close range.
4. Female/eclipse confusion: Both species’ females are mottled brown, but shoveler females have a broad, orange-tinged spatulate bill and a grey forewing in flight; wigeon females have a normal bill and a white upperwing patch.
5. Eclipse males: Shoveler eclipse males resemble females but retain the blue forewing; wigeon eclipse males lose bright head colors but keep the white upperwing patch.
6. Leg color: Shoveler legs are bright orange-red; this is less useful at a distance but can help in close views.
7. Feeding behavior: Shovelers often feed by sweeping their bills side to side at the water’s surface; wigeons graze more on land and dabble less actively.
8. Flocking: Wigeons are more likely to be seen in large, dense flocks; shovelers are less gregarious and often in small groups.
9. Habitat context: If you see a duck feeding by filtering invertebrates from muddy water, suspect shoveler; if grazing on grass, suspect wigeon.
10. Size is not reliable: Both are medium-sized dabbling ducks and can overlap in apparent size.
11. Juvenile/immature confusion: In flight, focus on the forewing color (grey in shoveler, white in wigeon) and bill shape.
12. Vagrant confusion: In regions where both species are rare, eclipse shovelers can be confused with female wigeons, but the bill shape and forewing color remain reliable.
13. Speculum color: Both have a green speculum, but the shoveler’s is bordered by white and blue/grey forewing, while wigeon’s is bordered by white upperwing patch.
14. No reliable vocal differences noted in these sources.
15. **When in doubt, prioritize bill shape and forewing color in flight for all ages and sexes."

Both species are similar in length and mass: Northern Shoveler measures 44–52 cm long with a wingspan of 70–84 cm, and Eurasian Wigeon is 42–52 cm long with a wingspan of 71–80 cm. Their weights overlap broadly (shoveler 500–800 g, wigeon 500–1,073 g). In the field, size alone is not a reliable separator, as both can appear medium-sized among dabbling ducks.

• Juvenile/immature/first-winter: Both species’ females and immatures are mottled brown, but the shoveler’s bill is always broad and spatulate, while the wigeon’s is normal in shape. In flight, female/immature shovelers show a grey (not white) forewing, while wigeons show a bright white upperwing patch and a dark green speculum.
• Adult breeding male: Shoveler drake has an iridescent dark green head, white breast, chestnut flanks, and a black spatulate bill. Wigeon drake has a chestnut head with a creamy crown, pink breast, grey flanks, and a normal bill. In flight, shoveler shows pale blue forewing and green speculum with a white border; wigeon shows a brilliant white upperwing patch and dark green speculum.
• Eclipse/nonbreeding male: Both species’ males resemble their females, but the shoveler’s pale blue forewing remains, and the bill stays broad. Wigeon eclipse males lose the bright head colors but retain the white upperwing patch.

Northern Shovelers often feed by swinging their bills side to side at the water’s surface, straining small invertebrates with their specialized lamellae. They are less gregarious than wigeons outside the breeding season and form smaller flocks. Eurasian Wigeons graze more on land and are often seen in larger, tightly packed flocks. Shovelers are more likely to be seen dabbling or filtering in shallow water, while wigeons may be seen grazing on grass or swimming in open water.

Both species use similar wetland habitats, but shovelers prefer mud-bottomed marshes rich in invertebrates, where their bill adaptation gives them a feeding advantage. Wigeons are more likely to be seen grazing on grass near water or in open wetlands. Both are widespread in the Palearctic, but the shoveler’s range extends further into North America, and it winters further south.