The Western Grebe, (Aechmophorus occidentalis), is a species in the grebe family of water birds. Folk names include "dabchick", "swan grebe" and "swan-necked grebe".
This is the largest North American grebe. It is 55–75 cm (22–30 in) long, weighs 795–2,000 g (1.75–4.4 lb) and measures 79–102 cm (31–40 in) across the wings.It is black-and-white, with a long, slender, swan-like neck and red eyes. It is easily confused with Clark's Grebe, which shares similar features, body size, behavior and habitat, and hybrids are known.
The Western Grebe has black around the eyes and a straight
greenish-yellow bill whereas the Clark's Grebe has white around the eyes
and an up-turned bright yellow bill. The downy young of Western are
grey; Clark's downy young are white.
Western Grebes nest in colonies of hundreds on large inland lakes, sometimes using coastal marshes, in western North America. It has a spectacular courtship display; two birds will rear up and patter across the water's surface. Northern birds migrate west to coastal ocean in winter; birds in the southwest and Mexico may be permanent residents.
This bird dines by diving for carp, herring, mollusks, crabs, and salamanders.
Western Grebe fossils from the Late Pleistocene of SW North America were described as a distinct species (Miller 1911), but later ranked as a paleosubspecies Aechmophorus occidentalis lucasi
(Howard 1946). More recent study found them to fall within the
variation now known to exist in today's birds (Jehl 1967, Storer 1989).
A large, elegant, black-and-white grebe, the Western
Grebe breeds in lakes and ponds across the American West and winters
primarily off the Pacific Coast. The very similar Clark's Grebe was long
thought to be the same species. Both species have a dramatic,
choreographed courtship display, in which the birds rush across the
water with their long necks extended.
Adult Description
Medium-sized waterbird.
Black back and face.
White neck and underside.
Long neck.
Long, thin bill.
Immature Description
Similar to adult.
Habitat
Western Grebes breed on freshwater lakes and marshes with extensive open
water bordered by emergent vegetation. During winter they move to
saltwater or brackish bays, estuaries, or sheltered sea coasts and are
less frequently found on freshwater lakes or rivers.
Length
21.7–29.5 in
55–75 cm
Wingspan
31.1–33.9 in
79–86 cm
Weight
28.2–63.5 oz
800–1800 g
Food
Western Grebes eat mainly fish, catching them by diving in open water.
They either spear prey or capture it with a forceps-like motion of the
bill, taking larger prey items to the surface before swallowing. They
also occasionally consume bottom-dwelling crustaceans and worms
(polychaetes).
Nesting
The nest looks like a solid mound with a shallow depression for the
eggs. It's built of plant materials from the bottom up, on a submerged
snag or floating in up to 10 feet of water and anchored to emergent or
floating plants. Rarely the nest is built on land using small amounts of
surrounding vegetation.
The nest is most often built on floating vegetation hidden among
emergent plants; Western Grebes occasionally nest in the open and rarely
on land. Both sexes build the nest using material brought from
underwater, found floating on the surface, or growing near the nest.
Western Grebes often nest in colonies, with hundreds or even thousands
on one lake.
Clutch Size
3–4 eggs
Number of Broods
1 broods
Egg Length
2.1–2.6 in
5.3–6.6 cm
Egg Width
1.4–1.7 in
3.5–4.2 cm
Incubation Period
24 days
Egg Description
Plain pale bluish, often stained brownish by sodden nest material.
Condition at Hatching
Alert and covered with blackish or silvery down; leaves nest and rides on back of parent after hatching.
Behaviour
The Western Grebe, like other grebes, spends almost all its time in
water and is very awkward when on land. The legs are so far back on the
body that walking is very difficult. Western Grebes are adept swimmers
and divers. Courtship happens entirely in the water, including a
well-known display known as “rushing,” where two birds turn to one side,
lunge forward in synchrony, their bodies completely out of the water,
and race across the water side by side with their necks curved
gracefully forward.
0 comments:
Posting Komentar