Bay Crossings Bay Environment
The Birds Are Coming! The Birds Are
Coming!
By Teri Shore
I spotted the
white-crowned sparrows in my Sonoma backyard in early October.
I was waiting for them. The little brown birds always arrive about this
time to feed in the trees around my house during the winter. The
black-and-white head stripes distinguish them from other sparrows. I don’t
know where they come from, but their arrival always marks the golden
transition from autumn to winter.
The sparrows are among the
thousands, even millions, of birds that travel the Pacific Flyway every
year. So it seemed a good time to investigate the flow of feathered
traffic into the Bay Area’s common backyard, the San Francisco Bay.
The San Francisco Bay
Estuary is the most important wintering estuary for aquatic birds on
North America’s Pacific Coast. Nearly half of the waterfowl and
shorebirds migrating along the Pacific Flyway pass through the Bay and
Delta. Waterfowl, such as ducks, geese and swans, and shorebirds,
including plovers, stilts, avocets and sandpipers, are now arriving in
large flocks. The South Bay is one of the most important winter feeding
grounds in North America.
As soon as I began my
research, it became obvious that I could not share the wonder and
expanse of the winter migration in one column. Instead, I’ll provide
an overview and highlight some species and the threats they are facing.
I also suggest that ferry
riders do a little research on their own by just looking out onto the
Bay during these coming months and look for birds that you don’t
normally see. Carry a pair of binoculars. Pick out a bird and look it up
in a field guide. You might be amazed.
The Bay’s World of
Birds
Over one million
shorebirds inhabit bay marshes annually. Ducks, geese, swans and other
waterfowl seek out shallow, sheltered open water such as sloughs and
bays to nest and rest along shores and feed on plants, seeds, snails,
clams and insects. Some, like the canvasback, seek out open water to
rest.
Waterfowl The
Bay Estuary is the winter home for 50 percent of the diving ducks in the
Pacific Flyway, with one of the largest wintering populations of
canvasbacks in North America. More than 30 species of waterfowl are
found in the San Francisco Bay ecosystem. Almost the entire California
population of migrating northern shovelers winters in the bay, as do
two-thirds of the greater and lesser scaups.
Nearly 90 percent of the
canvasbacks from Alaska winter in San Francisco Bay. Canvasbacks are
about the size of the common Mallard. The male canvasback is tri-colored
with a distinctive red head with blood-red eyes, mostly white body and
black breast and tail. The females are less showy with a brown head and
eyes and dusky gray body. They tend to congregate in the mouths or
rivers or channels, large wetlands and brackish marshes. The protection
of this species was one of the main reasons for establishing the San
Pablo Bay National Wildlife Refuge in the North Bay.
Sadly, canvasbacks are
decreasing. In the 1960s, 60,000 birds were counted. By 1990 the count
declined to 24,000. Scientists believe that canvasbacks suffer from
toxic contamination in the food chain, as they feed on clams that
contain high levels of selenium. Boats, aircraft, people and pets also
disturb canvasbacks.
Total waterfowl numbers in
the San Francisco Bay Estuary has dropped from a record high of 1.3
million in 1977 to a low of 109,000 in 1982 (with a mean annual
population over the same period of 390,532). Populations of dabbling
ducks and geese are at an all time low due to drought, predation and
habitat loss.
Shorebirds
The SF Bay Estuary is an important wintering and migratory stopover site
for shorebirds such as plovers, stilts avocets and sandpipers. It
attracts more migrating shorebirds than any other wetland area in
California. At least 34 species live, nest and forage for food along the
Estuary’s shore, many equipped with long bills and legs useful for
foraging in the mudflats. Some of these birds are thriving, and others
struggling. The long-billed curlew is declining due to habitat loss and
drought. The black-necked stilt, American avocet and Wilson’s
phalarope appear to have been increasing in response to tidal marsh
conversion into salt ponds suitable for nesting and raising young. Many
shorebird populations, including the endangered clapper rail and black
rail, are suffering from red fox (a non-native species) predation.
When it comes to ferry and vessel traffic, some researchers say that
wintering ducks and other waterfowl seem fairly tolerant of boat
disturbance. But the effect on these waterfowl has to be assessed and
minimized, or avoided as the ferry system expands. The potential impacts
on shorebirds are also an important consideration that must be studied
before new ferry service begins.
For more information
consult:
The San Francisco Bay
Estuary Institute website www.sfei.org/
California Department of
Fish & Game website, www.dfg.ca.gov
Baylands Ecosystem: Species and Community
Profiles published by the San
Francisco Bay Area Wetlands Ecosystem Goals Project (January 2001)
