Biology Reference
In-Depth Information
with an abiding interest in wetland birds, and the author of California Bird
Life . “It's part of a network that's built into the life history of these critters.
Their wintering grounds are just as important as their breeding grounds.
These birds tie the continent together.”
Waterbirds begin arriving in the bay in August. More than 50 percent
of the diving ducks traveling the Pacific Flyway winter here, as well as one
of the largest populations of Canvasbacks in North America. Biologists
and volunteers counting birds from shorelines, boats, and airplanes have
tallied up more than 700,000 waterfowl in the bay and delta in recent win-
ter surveys. And more than a million shorebirds—the sandpipers, plovers,
phalaropes, and dowitchers that wade in the water and probe the mud for
food—are estimated to take up winter quarters in the bay each year. Most
won't leave the estuary until April.
The 30 species of waterfowl commonly found in the bay can be divided
into several distinct groups. Swans and geese feed on plants by grubbing in
the sediments of wetlands and fields. Dabbling ducks feed by filtering
small invertebrates and plants from surface waters or by tipping tail-end-
up to yank plants from the shallows. Today the most abundant dabblers in
estuary waters are Mallards and Cinnamon Teal, but historically Northern
Pintail dominated the scene.
Another group is the diving ducks. These species use legs set far back
on their bodies to propel themselves underwater after fish or to pick mol-
lusks and other food of the bottom. These ducks may dive to depths of 40
feet. The abundance of fish and relative scarcity of plants in the bay's open
waters mean that diving ducks here outnumber dabblers two to one.
Many other types of birds use the bay's shores and creeks as critical rest
and refueling sites. Still other species breed to the south, rather than the
north, and live in the bay the rest of the year. These include the prehis-
toric-looking Brown Pelicans that fly in bomber formation around the
bridges and shores. Many seagulls and cormorants—marine birds—also
frequent the bay.
Bufflehead
The most diminutive of the bay's native ducks is the Bufflehead ( Bucephala
albeola ), also nicknamed the “butterball” or the “bumblebee dipper.” The
male, or drake, of this black-and-white duck has a disproportionately large
domed head that inspired the species' original name: the buffalo head.
Buffleheads make a strenuous autumn flight from the midwest or from
northern boreal forests to the California coast. Upon arrival, these diving
ducks must first rest and recover, and then they must eat enough clams,
shrimp, snails, and seeds to build up fat reserves for the return flight. Over
the next several months, some will indulge enough to amass a quarter of
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