Enjoy and see you on the water!
Newman
Joseph Abbate
Barrier Island Ecology
Shorebird Profile
Black Skimmer (Rynchops niger)
Shorebirds
contain 18 families and 300 species worldwide, and 7 families occur in North
Carolina. Shorebirds
main order is charadriiformes. Charadriiformes
species are grouped into four main families due to structural characteristics
like skull formation, vertebral column, and syrinx( vocal
chords). The four distinct suborders include: Charadrii (plovers, oystercatchers), Scolopaci (sandpipers, willets,
curlew), Alcidi (puffins ,auks) and Lari
(gulls, terns, skimmers, auks). Shorebirds species diversity, coastal adaptations, and
colonial breeding grounds near human inhabitance make them a valuable species
for conservation research. This
manuscript will explore the life history of one species of shorebird, the Black
Skimmer (Rynchops niger ), current conservation
status, and highlight a North Carolina conservation program .
Three species of skimmer occur world wide, the African (Rynchops
flavirostris) the Indian (Rynchops albicollis), and the Black
(Rynchops niger). The Black Skimmer has three subspecies
occurring in North and South America. R.
n. niger breeds on the Atlantic coast of North
America, and from Southern California to Ecuador. R. n. cinerescens is larger,
breeds in Northern Venezuela to the Amazon Basin. R. n. intercedens
occurs on the rest of the Atlantic coast of South America south to central
Argentina. The two southern races, R. n.cinerescens,
and R.intercedens nest primarily on
inland river bars, and inhabit mostly freshwater environments, while R.niger is restricted to coastal barrier
islands, and salt marsh estuaries.
Skimmers of the Atlantic
coast stage for migration on sand bars and beaches until till mid –December,
and winter on the gulf coast of Florida. Southern skimmer populations migrate
to Caribbean, and coastal beaches of Central and South America in winter and
return to breeding grounds in late March.
Atlantic skimmers
arrive on breeding grounds during late April early May. Skimmers nest in a colonial
breeding fashion, with multiple scrape nests per pair located within less than
a meter from one another. The nest site
selection predominately occurs on the beach face adjacent to the primary dune,
and at the foot of dune slacks. The skimmers usually intermingle breeding
grounds with several tern sp. seemingly for added early defense mechanisms
against predation. Furthermore, Gill (1994) explains that a benefit of breeding
in a colony is greater predator detection, and removal.
Individual male skimmer excavates a “Scrape Depression”
in the sand where the female will lay a 4-5 egg clutch. The eggs of the skimmer
are cryptically colored to blend in with the sand/shell grains on the beach
aiding in predator avoidance. In addition, skimmers, unlike most shorebirds,
have a unique ability to renest or double brood if encountered with sudden nest
destruction. For example, if high tide washes out the nest, the skimmers will
automatically begin copulation and renest. Nest sight selection depends on the availability
of high quality beach sand, sparse vegetation, and lack of human presence. Studies
have proven that colonies less subject to human fiction yield higher fledging
ratio per season ( Gochfeld,1978). Moreover, (Gochfeld,1977),
indicates that pre-laying skimmers may abandon a colony that is frequently
disturbed. Incubation is shared by both adults and lasts
for approximately 22 days. Black Skimmer
has precocial chick development, where within hours after hatching, the
fledgling has the ability to move and receive food from parent.
Black Skimmers
usually are recorded foraging at dawn/dusk at low tide (Erwin, 1977). Nocturnal
foraging is common with this species, and places them apart from most shorebird
species. (Rojas et al. 1997) ascertained that the skimmer had a 5:1 rod /cone
ratio when compared to Ibis with a 3:1 rod/cone ratio. The study suggests that
skimmer having almost double the rod concentration in the retina when compared
to other birds is better equipped for foraging in low light regimes, as well as
complete darkness. In addition, the study pointed out the reason for the small
pupil when compared to other shorebirds is because of the tactile feeding
mechanism of the R.niger compressed
mandible. Furthermore, the author strongly inferring that Skimmer’s detect prey
by beak feel and not by sight hence the smaller size pupil. Moreover, the
skimmer is the only bird to close its pupil into the form of a vertical slit
under changes in light. This compression of the pupil during low and high light
is similar to the change in a feline pupil under changing light conditions.
Research has also suggested that the constriction of the pupil serves to both
enhance light absorption for nocturnal foraging and protects the pupil during
bright light exposure (Rojas et al.1997). Skimmers obtain prey by immersing the
lower bladelike mandible in the water while cruising along mud flats, marsh
edges, and tidal creeks. The Skimmers
beak closure depends on a tactile stimulus. Similar to the trigger hairs on a
Venus Fly Trap, the skimmers beak shuts upon touching anything encountered
while skimming for prey. Erwin (1974)
found during observations that skimmers capture prey items every 5 minutes during
foraging missions. The common prey items captured by skimmers consist of planktonic
fish species (minnows, killifish and herring) in the upper water column.
Skimmer populations
in the early 1800’s were impacted largely by the “egging” industry. Commercial
egg production operations raided skimmer nesting colonies harvesting eggs by
the bushel. In addition, the gregarious nature of the skimmer during breeding
made them a prime target for market hunting of the in the early 1900’s.
Today, the Black
skimmer’s specialized beak and eye structure, unorthodox foraging style, and
reproductive modes make them a species of concern within its entire range. The states
of New Jersey, as well as the state of Florida, have classified the Black
Skimmer as endangered. North Carolina classifies them as species of concern,
and has developed a new conservation program to manage all breeding areas
throughout the NC coast
North Carolina Wildlife Resources and Audubon
Society understanding the current national decline in the Black Skimmer populations
created a conservation program named the Important Bird Areas of North Carolina
(IBA’s). IBA’s main objective is to
protect and preserve habitat where high species diversity and richness is
present. The program begins with the employment of seasonal Warden/Biologist assigned
to each coastal IBA area. The biologist facilitates both management objects and
guided environmental outreach daily. The warden’s shorebird management duties
consist of nest and fledging monitoring, roping off nesting areas, predator
trapping and managing people and dogs near the perimeter of the skimmer colony.
Environmental education is conducted in schools and at the breeding colony. The
goal of the education is to inform the public about
shorebirds and suggest strategies on how people can reduce their impact on the
breeding colony at the beach. Locally, in New Hanover County, two Black Skimmer
IBA’s exist. One on the south end of Wrightsville Beach, and the other on the
south end of Hutaff Island, each located adjacent to inlet waterways. Both areas are about 3 acres in size and
comprise all of the breeding Skimmers in the Cape Fear Region.
The Black Skimmer
story in Carolina is a positive one, however, globally, the viability of this
population for the future is in question.
References
Erwin, R.M.
1977. Black skimmer breeding ecology and behavior. Auk 94:709-717.Gill.F.B,1995. Ornithology.W.H. Freeman and Company.
pp.384-385
Gochfeld,M. 1978. Colony
and Nest Site Selection by Black Skimmers. Proceedings of the Colonial Water
bird Group
Vol. 1, (1978), pp. 78-90
Vol. 1, (1978), pp. 78-90
Luz Marina Rojas, Raymond McNeil, Thérése Cabana and
Pierre Lachapelle. 1997. Diurnal and Nocturnal Visual Function in Two Tactile
Foraging Water birds: The American White Ibis and the Black Skimmer. The
Condor 99:191-200
Richard l. Zusi and David Bridge, National Museum of
Natural History, Smithsonian Institution, Washington DC 20560,received Dec 8
1990,accepted 21July 1981
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