Biology Reference
In-Depth Information
At water's edge, Jeffrey tunes the receiver to the frequency of his target bird,
sweeps the antenna in the direction of the marsh, and listens. The pings get louder
when the antenna is pointing directly at his quarry, allowing him to home in on the
rail's location by moving the antenna in an arc. He refines his position by marking
with an outstretched arm where the pings drop off to nothing, then recenters his
aerial. When he's satisfied the reading is accurate, he uses a compass and GPS to
mark the bearing. He'll repeat measurements for each bird several times as he
walks the shoreline paths. Back at the lab, a computer program will triangulate the
readings and rate the reliability of each data point. Jeffrey and another technician
may take readings several times a day at up to three marshes—once at high tide
and once at low tide—to get an idea of the birds' ranges and behavior.
Arrowhead Marsh consists largely of salt-marsh cordgrass, the clumps resem-
bling shocks of hair on a bed-tousled head. Also known as spartina, cordgrass is a
mainstay of Clapper Rail life. It offers both cover from predators and building ma-
terial for nests in a habitat with relatively few other plants.
The success of this cordgrass, a hybrid of native and Atlantic species, is the
impetus behind Overton's study. Clapper Rails have been found nesting in the hy-
brid, and scientists are concerned that programs to eradicate the hybrid could be
hurting the birds.
The rail study began in 2006. Census numbers have recorded a sizable recent
rise in rail populations in the bay, from a low of a few hundred in the early 1990s
to about 1,400 in 2008. The study should help sort out whether the extra cover af-
forded by hybrid spartina is responsible for the comeback.
Another goal is to determine how many California Clapper Rails local marshes
can support. Arrowhead houses a goodly number. Every 20 minutes or so, another
bird pops out of the cordgrass or stalks across the expanse of mud alongside the
pier. Rails are so plentiful here that it's hard to remember the species is endan-
gered.
The biologists wait for the rails to settle down and nest. According to Jeffrey's
tracking, none has laid its clutch of eggs yet, though plenty of birds are showing
signs of spring fever. We hear a smattering of the
keck-burr
come-hither calls that
females use to solicit males, and we see two of these normally cover-conscious
birds bickering in the open mud at the end of the pier. We spot a couple of other
resident rails driving intruders from their patch of cordgrass. During breeding sea-
son, territory defense attains extra importance because pairs rely on that portion
of marsh to support their young.
The birds time egg laying very closely to the tides, to avoid the big surges that
can drown their eggs. “Just a few inches higher makes a huge difference if you live
in a marsh,” Overton says.
The rails' susceptibility to tidal flooding and thus climate change worries Over-
ton and other biologists. But for the moment, these homely avians—the focus of so
much human worry and effort—continue to reside in local marshes, thrilling visitors
with their boisterous cries.
KMW
