コサギ 対 ダイサギ

要点

The most reliable way to separate Little Egret from Great White Egret in the field is by bill and leg color: Little Egret shows a slender black bill and black legs with yellow feet, while Great White Egret has a yellow bill and black legs and feet. Size is also a strong clue—Great White Egret is much larger and bulkier, but beware lone birds or distant views. In breeding season, Little Egret develops long, wispy nape and breast plumes, while Great White Egret sports delicate ornamental back plumes. Juveniles of both species look similar to non-breeding adults, so focus on structural and bare-part differences. Both are all-white, so careful attention to these details is essential.

識別のコツ

1. Bill color: Little Egret has a slender, entirely black bill; Great White Egret has a stout, yellow bill (may darken slightly in breeding season but remains thicker and yellower than Little Egret). This is the single most reliable mark at all ages and seasons.
2. Leg and foot color: Little Egret has black legs with bright yellow feet (juveniles: greenish-black legs, dull yellow feet); Great White Egret has black legs and black feet. Always check the feet if visible—yellow feet are diagnostic for Little Egret except in certain subspecies (nigripes: blackish feet).
3. Size and structure: Great White Egret is much larger, taller, and bulkier with a longer neck and heavier build. Little Egret is noticeably smaller and more delicate. Use direct comparison if both species are present.
4. Breeding plumes: In breeding season, Little Egret shows two long, wispy nape plumes and elongated scapulars; Great White Egret develops long, lacy ornamental plumes on the back. These are best seen at close range or in good light.
5. Bare-part color in breeding: During peak courtship, Little Egret's lores turn red and yellow feet may flush red; Great White Egret's bill may darken slightly, but legs and feet remain black.
6. Juvenile confusion: Juvenile Little Egrets look like non-breeding adults but may have a greenish tinge to the legs and duller yellow feet. Juvenile Great White Egrets are white with yellow bills and black legs/feet, matching adults. No distinctive flight pattern differences in immatures.
7. Flight profile: Both fly with necks retracted, but Great White Egret appears longer-winged and heavier in flight; Little Egret is more compact and agile.
8. Foraging behavior: Little Egret often uses active foraging (shuffling feet, running), while Great White Egret is more stately and slow-moving, but this is not always reliable.
9. Habitat overlap: Both species may occur together in wetlands, so do not rely on habitat alone.
10. Plumage color: Both are entirely white at all ages; do not use overall whiteness as a separator.
11. Vocalizations: Not reliably separable by voice in the field.
12. Subspecies pitfall: In the nigripes subspecies of Little Egret (rare outside Asia/Australasia), feet may be blackish rather than yellow, so rely more on bill color and size in those cases.
13. Direct comparison: If both species are present, the size and bill/foot color differences are striking when seen side by side.
14. Distant birds: At long range, focus on bill color and structure, and overall size if a direct comparison is possible.
15. Mixed colonies: Both may nest together—always check each individual carefully, especially in expanding ranges.

大きさ

Great White Egret is substantially larger than Little Egret. Little Egret averages about 532 g in body mass, with a length of 55–65 cm and a wingspan of 88–106 cm. Great White Egret is much heavier (typically around 1,000 g), longer (80–104 cm), and has a much broader wingspan (131–170 cm). In the field, Great White Egret appears taller, longer-necked, and bulkier overall, while Little Egret is more delicate and compact. However, size can be misleading if birds are alone or at a distance, so always confirm with other marks.

羽色

Both species are all-white at all ages and seasons, so plumage alone is rarely diagnostic except in breeding adults. Little Egret in breeding plumage shows two long, thin nape plumes ("aigrettes"), elongated scapulars, and some breast plumes, while Great White Egret develops long, lacy ornamental plumes on the back. Juvenile and non-breeding Little Egrets lack the full breeding plumes and may show a hint of greyish or brownish feathers, but are otherwise white. Juvenile Great White Egrets look like non-breeding adults—entirely white, with no special markings. There are no distinctive age-specific upperwing patterns in flight for either species, so rely on bare-part color and structure.

行動

Both species feed in shallow water and may use similar foraging techniques, such as stalking, running, or standing still to ambush prey. Little Egret is noted for more varied and active feeding strategies, including shuffling its feet to disturb prey and sometimes associating with cormorants or livestock. Great White Egret tends to walk with its neck extended and wings close to the body, and its flight is slow with the neck retracted. Both species are colonial nesters and may be seen together in mixed groups, especially where ranges overlap.

生息環境

Both egrets are found in wetlands, marshes, and shallow water habitats. Great White Egret has a wider global distribution, occurring across the Americas, Africa, Europe, and Asia, and is increasingly found in northern Europe. Little Egret is also expanding its range, including into the New World. In areas where both occur, they may share the same habitats and even nest in the same colonies, so habitat alone is not a reliable separator.

声

Great White Egret is generally quiet but may give a low, hoarse croak or a loud 'cuk cuk cuk' at breeding colonies. Little Egret's vocalizations are not described in these notes, and voice is not a reliable field mark for separating these two species.