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Western Grebe Aechmophorus
occidentalis
Typically migratory birds travel north in spring and south in
fall. The western grebe is atypical in its migratory routes.
It migrates east and west between Prairie marshes where it
breeds and the winter quarters on the Pacific Coast of western
Canada and the USA. The western grebe is the largest grebe in
the north Pacific Ocean weighing about 800 grams. They
assemble in large flocks in coastal waters from southern
British Columbia to Baja California. Major winter areas on the
Pacific
Coast include Strait of Georgia, BC, Puget Sound, Washington
and San Francisco Bay, California.
References
Storer, R. W., and G. L. Nuechterlein. 1992 . Western Grebe (Aechmophorus
occidentalis), The Birds of North
America Online (A. Poole, Ed.). Ithaca: Cornell Lab of
Ornithology; Retrieved from the Birds of North America.
Grebe Behaviour
Migration
Western grebes migrate at night in flocks. Grebes that winter
in British Columbia and Washington fly to the Pacific coast
between early September and early November and return to
breeding grounds from late April to early May. Some grebes
reside in the southwest and western USA. Grebes banded at
Delta Marsh in Manitoba were later recovered on the Pacific
coast from southern British Columbia to San Diego.
Hunting & Foraging Behaviour
Western grebes frequently peer into water to search for prey
or potential predators. They dive to pursue fish. On the
Pacific Coast, western grebes feed regularly on
sandlance and
Pacific herring
that they pursue at night. The western grebe is unique among
grebes in that it has a spearing mechanism that allows for
rapid extension of the neck similar to herons and anhingas.
The structural details are not worked out nor are the details
on how it is used in the wild. It seems that most fish are
captured by forceps-like action of the bill. Large fish are
brought to surface before being swallowed.
Nesting Behaviour
Western grebes nest in loose colonies. They are highly
gregarious in all seasons and nesting colonies of up to
several thousand birds have been reported although pairs nest
singly or in small groups on occasions. Grebes defend
territories around the nest by chasing all species away from
immediate vicinity of nest. The pair bond is maintained until
the chicks are several weeks old. At that time the pair
sometimes split the brood.
Western grebes are best known for their courtship ceremonies.
These displays are well documented and have been described as
the Rushing Ceremony and Weed Ceremony (Nuechterlein
and Storer 1982). During the Rushing Ceremony, two
birds swim side by side and then lunge forward with the body
completely out of water to run rapidly across the water for up
to 20 meters. The wings are lifted but not extended. The run
ends with a dive. The Weed Ceremony occurs late in
pair-formation. The grebes usually stare at one another while
in an erect posture with the crest raised and bill held nearly
horizontal. As the display proceeds the posture becomes more
rigid. From this neck-stretched posture, one or both of the
grebes suddenly dives to return to the surface with weeds
still in the erect posture. When both grebes have weeds, they
approach each other with feet churning the water to rise into
a vertical posture with most or all of their bodies out of
water. The necks are outstretched and the bills raised above
the horizontal. The grebes move slowly forward, sometimes
spiraling, while their heads rotate from side to side. The
display ends when one grebe discards its weeds. For detailed
descriptions, see Storer and Nuechterlein (1992).
Vocalizations
Western grebes utter many calls. Storer and Nuechterlein
(1992) describe an advertising
call:
a harsh, rolling cree
creet often given by courting birds either
spontaneously or in answer to potential courting partners; a
Ratchet call: a loud, harsh trill given alternately
with another grebe; a Threat call: a repeated
tuk-tuk-tuk while
defending a nest; and a Copulation Duet: a loud trill
given by male with regular interspersed shorter call notes by
female during copulation.
Science
Much of the research of western grebes has been made at their
breeding marshes. Far less is known about the grebes on the
Pacific Coast wintering grounds. Population trends in
Christmas Bird Count data collected by volunteer birdwatchers
are equivocal depending on which counts are used in the
analysis. For BC, Washington and California regions, grebe
numbers dropped until the late 20th century after
which they stabilized or increased. But in
Puget Sound, the
large flocks counted in 1992 are now apparently absent. The
sudden change in abundance of western grebes might reflect a
real decline in numbers or the mobility of grebes over the
years. PWLF is researching this question in the
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