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Shorebird Profile: Black Skimmer (Rynchops niger)

18 Nov Posted by in Blog, shorebird | Comments
Shorebird Profile: Black Skimmer (Rynchops niger)
 

Hey Birders!  This may be a longer post, but I wanted to share some of Capt. Joe’s research writing about the Black Skimmer.  Below is a paper Joe wrote last week for his class at UNCW.

Enjoy and see you on the water!
Newman

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 subspeciesoccurring 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. intercedensoccurs 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

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

http://myfwc.com/media/1351505/Black%20Skimmer%20Final%20BSR.pdf

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