Biology Reference
In-Depth Information
Whether after large or small prey, these seals' talent for following
hydro-trails is particularly useful in local waters, where visibility often
drops to a few feet or less. Studies of their gut contents suggest these seals
eat goby, sculpin, and croaker in the extreme South Bay but focus on the
Plainfin Midshipmen of the Central Bay. This single fish makes up over 90
percent of local Harbor Seals' diets. Perhaps the unique luminescence of
these fish gives them away in the murky water.
Like their human neighbors, bay seals thrive on the variety of the local
cuisine. Allen once saw seals eating a halibut that was about the size of a
pizza. They were out of the water on Castro Rocks, holding the halibut in
their flippers and rotating the fish, “eating it around the edges like a choco-
late chip cookie,” she says.
Of the many types of bay life, perhaps the most visible to humans are
waterbirds. These aquatic avians include the ducks, sandpipers, gulls,
egrets, and other birds that can be seen year-round seeking food, rest, and
shelter on bay waters and shores.
Waterbirds fall into different categories based on their habitat usage.
Shorebirds include the skittish, flighty birds that sprint across the sand
and probe at water's edge for insects and crustaceans. Seabirds such as pi-
geon guillemots, gulls, and cormorants frequent the open bay or ocean,
diving for their fishy dinners and often nesting on rocky offshore islands.
Another common category of waterbirds, waterfowl, encompasses ducks,
geese, and other aquatic game birds. Some waterfowl live on the open
ocean, but more of them frequent estuaries such as San Francisco Bay, as
well as brackish and freshwater lakes.
Waterbirds flock to the California coast for much the same reason peo-
ple do: the mild winters. Species winging in from the arctic arrive by the
millions every year to rest in the shallows and wetlands of San Francisco
Bay. The bay provides critical refueling and foraging habitat for vast num-
bers of shorebirds that breed on arctic lakes, as well as for waterfowl that
have raised their young on North American prairies and in northern
woods. As soon as the air cools around their nesting sites, these travelers
take flight for the long journey to estuaries and wetlands of the temperate
coast. As the biggest estuary along the Pacific and the one with the widest
variety of habitats, San Francisco Bay is the destination of many. During
peak migration periods, up to a million shorebirds may pass through the
bay in a single day.
“San Francisco Bay is not discrete,” says Jules Evens, an avian ecologist
