During the new and full moon tides of April and May
female horseshoe crabs come to bays and inlets along South
Carolina’s coast to lay eggs in the sand. The eggs are energy
rich and easily digestible, so they make a wonderful food
source for shorebirds. The beaches of Seabrook and Kiawah
have too much wave action for horseshoe crab spawning, so
the crabs seek out more sheltered beaches in which to lay.
Instinctively the red knots know when the crabs have arrived,
and in a mass exodus, they leave Kiawah and Seabrook when
spawning begins to dine on horseshoe crab eggs.
Overall, the number of red knots has declined nearly
85 percent over the last 15 years, and because of this drastic
population decline, the red knot has been listed as threatened
under the Endangered Species Act. Reasons for this decline
may be influenced by food availability especially during
migration as well as disturbance.
Biologists with the South Carolina Department of Natural
Resources (SCDNR) have researched red knots for several
years to understand the role that South Carolina plays in their
journeys. Documenting how red knots use South Carolina’s
resources may help efforts to conserve this vulnerable species.
Biologists and many volunteers have been capturing knots
to measure them and place field-readable engraved bands on
their legs. Unique markers on each bird allow biologists to
track individual birds if they are re-sighted anywhere in the
hemisphere.
Biologists with SCDNR and U.S. Fish and Wildlife Service
in partnership with Dr. Larry Niles and Ron Porter and
many volunteers also have placed geolocators on some of the
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captured knots. Geolocators are small, electronic devices that
measure and record light levels to determine global location.
Geolocators are a valuable tool to study bird migration routes
and identify staging areas, although birds must be re-captured
to obtain the data from the devices.
In the spring of 2017 SCDNR also tagged knots with
nanotags. Nanotags are tiny radio transmitters that emit a
unique pulse that can be detected by Motus Wildlife Tracking
System towers. Bird researchers have placed these towers
along migration routes, and the tagged birds are recorded as
they pass. These tools help researchers understand different
migration patterns or routes these birds use in an effort to
develop management plans. Location information from the
geolocator and nanotag projects indicates that some of the
knots leave South Carolina in the spring and fly directly to the
Arctic. This information identifies South Carolina beaches as
very important for red knot and other shorebirds survival!
Despite the large flocks sometimes present on our beaches,
most shorebird species are declining. Because large numbers
of shorebirds often concentrate in a single location at a
stopover site, they are vulnerable to disturbance. Joggers,
beachcombers, bicyclists, and off-leash dogs can flush birds
that are feeding and roosting causing them to expend energy
in flight. This may hinder their ability to build enough fat
reserves for their migration journey.
We look forward to helping to make beachgoers more
aware of these amazing animals.
The residents of Kiawah and Seabrook should be proud
that these remarkable creatures visit their beaches. NK
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