Biology Reference
In-Depth Information
MIGRATIONS: WINGING IT WITH A PEEP
It is early August, and the male Western Sandpiper is nearly starving. He has flown
over 400 hundred miles since his last stop in Coos Bay, Oregon, many hours ago.
He began his trip south a week earlier in the Kuskokwim Delta of Alaska, more
than 1,800 miles to the north. At this moment he is flying into the southerly
breeze alongside thousands of his fellows on the avian highway known as the Pa-
cific Flyway. Below, the glint of the sun off San Francisco Bay is blinding, but his
journey is nearly done.
He soars above the roar of Dumbarton Bridge, alighting on a mudflat on its
eastern edge amid a handful of other shorebirds. Barely settled, he plunges his
beak rapid-fire into the mud to fill his empty belly. He has escaped the clutches of
raptors and made safe harbor here to spend another winter.
This male sandpiper is hardly the first of his kind to arrive this year. He has
been preceded by other birds whose nests failed, their eggs or chicks snapped up
by foxes and jaegers, as well as by the females, who left in late July right after their
eggs hatched. His mate was among them, using San Francisco Bay as a brief
stopping point on her way to a balmy winter in Panama. After the females de-
parted, he and the other males remained behind for several weeks to finish raising
their chicks. The youngsters will follow their parents south several weeks later. Male
sandpipers typically spend their winters at higher latitudes, where they will have a
head start in their spring quest to secure a good nesting site.
For the next few months, the male's life is dictated by the tides. Day or night,
he probes the muck with his sensor-laden beak to sniff out the clams, worms, am-
phipods, and other morsels hiding below. At other times, he uses the pointy, brush-
coated tongue only males have to mop up the nutritious slime known as biofilm
that coats the muddy surface. Biologists call this behavior “snot feeding,” after the
gooey texture of this mixture of single-celled organisms. Calories from biofilm may
constitute half of a sandpiper's diet.
At high tide, the male sandpiper retreats from the mudflats to the drier territory
of the salt ponds to roost, or drops in on nearby salt ponds for a meal. The sur-
rounding levees can be black with swarms of tasty Brine Flies and fatty fly larvae.
When the waters in the ponds are shallow enough, he may also indulge in “twin-
kling”—hovering above the surface to stab at wriggling balls of Brine-Fly larvae and
the occasional Brine Shrimp without getting wet. When the ponds are nothing but
mud, he joins thousands of others like him to forage on the oozes.
Though accustomed to long-distance travel, sandpipers are homebodies once
they reach their destinations. Over the 10 months the male sandpiper lingers in
the bay, he hardly budges from the same four square miles he visited last year and
the year before that.
When it's time to roost, he picks his way along the wrack-littered edge of one
of his chosen levees, raising a cloud of Brine Flies with each step, until he settles
amid other birds in a place where he can easily spot the approach of predators.
