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New Jersey Endangered and Threatened Species Field Guide
Species Group: Bird
State: Special Concern (Breeding)
Caspian terns are large, gull-like terns (about 21 inches in length) that have a black cap; a massive blood-red bill (sometimes darker at the tip); black legs; and a short tail that is slightly notched. It has white underparts and a gray upper body, and wings that are broad with an extensive dark patch on the wing tips (on the underside). In the winter, birds will look similar, but the cap is blotchy, gray, and extends over the forehead to the bill. Juveniles resemble non-breeding adults, but have an orange bill and dark marks across base of neck, back, and scapulars (one of the feathers covering the shoulder of a bird). Males and females look similar in coloration and cannot be distinguished externally. Caspian terns are most similar to royal terns (Thalasseus maximus), but about 20 percent larger.
Caspian terns are highly vocal with numerous calls including a rau or rrau, the most commonly heard call in an undisturbed colony. Alarm calls are a loud, barking ra, ra, ra, raeu, rra. Caspian terns also produce aggressive sounds such as short hard aeh, aeh or kraeh, kraeh in quick succession that may turn into hard, buzzing rro-rro-rra-rrerrerre.
DISTRIBUTION AND HABITAT
Caspian terns breed in scattered locations within six regions of North America. On the Atlantic coast, colonies are found in Labrador; Newfoundland; Quebec; and then the coast of North Carolina on islands near Oregon Inlet, a few pairs along Virginia’s barrier islands; and previously in Florida at Merritt Island National Wildlife Refuge. There have only been isolated occurrences of Caspian terns breeding in New Jersey. Caspian terns on the Atlantic and Gulf Coasts winter from southernmost North Carolina south around Florida (mostly absent from the Panhandle), west to south Texas, and south to the coast of Mexico and north Honduras. The wintering range also extends inland in these areas.
Caspian terns nest singly or in colonies or within/near other terns such as gull-billed (Gelochelidon nilotica), least (Sternula antillarum), royal, common (Sterna hirundo), Forster’s (Sterna forsteri), and Sandwich terns (Thalasseus sandvicensis); also black skimmer (Rynchops niger), American avocet (Recurvirostra americana), black-necked stilt (Himantopus alexandrus), brown pelican (Pelecanus occidentalis), and double-breasted cormorant (Phalacrocorax auritus).
Caspian terns use an assortment of substrates for breeding on barrier islands such as salt marshes and coastal estuaries, but they generally prefer open, flat, and sparsely vegetated areas. They may nest on sand, marshy soil, or pebbly shores. Wintering habitat includes beaches, isolated spits, impoundments, and managed wetlands.
Caspian terns feed on fish caught by diving entirely into the water. They may also snatch up fish off the surface of the water or steal fish from other seabirds.
Caspian terns arrive on their breeding grounds from late March to late May. Some terns form pairs before they arrive on their breeding grounds.
Both the male and the female will participate in scraping to make a nest. They may make several scrapes, but they will only use one for their nest. Tern nest sites appear to be influenced by both elevation (higher sites selected to avoid flooding) and proximity to other terns. Areas that are elevated greater than 2–3 meters above water level and free of vegetation are preferred. Sand is scraped to form a depression and then lined with bits of shells, dried vegetation pebbles, or other debris. Two to three weeks after they arrive, terns will begin laying their eggs. The egg-laying period lasts approximately 4 to 5 weeks. Terns will lay 1-3 eggs that are oval and pinkish or buff colored with darker markings, spots or blotches. The eggs are incubated for approximately 25-27 days by both the male and the female.
The hatched young are covered in downy feathers and will spend the first week of their life in or nearby the nest, but are highly mobile after that. Chicks are fed by both parents and ready to fly between 28–35 days old. However, parents will continue to partially feed immature terns for several months, as Caspian terns are cared for by parents much longer than any other tern species.
CURRENT STATUS, THREATS, AND CONSERVATION
Substantial declines have occurred since the late nineteenth century for Caspian terns along the Atlantic Coast. In some areas populations were hurt by egg collectors and hunters for the use of their feathers, and have not recovered. Other nesting colonies along the Atlantic Coast are small (about 100 pairs or less), but are stable or increasing. Population increases are occurring at sites where high-quality artificial habitat exists.
During New Jersey surveys (a one-time aerial survey on a given year), individual Caspian tern counts ranged from 0 to 55 birds between 1985 and 2011 (data provided by the NJ Endangered and Nongame Species Program, 2011). Note: The counts only capture a snapshot of the population in the Atlantic coastal marshes in a given year and only include birds associated with a colony. Surveys are not conducted each year and are not considered to be statewide, comprehensive efforts, but rather serve as an index of the population over time.
Limited nest sites, flooding, human disturbance, and predation are major factors contributing to the decline of this species. Effective management may include providing artificial nest sites (e.g., dredge spoil islands), habitat management of existing sites, nest protection, predator control, vegetation management, and reducing or eliminating public access to nesting sites. Long term conservation may also include protection from development.
Text derived from:
- Cuthbert, Francesca J. and Linda R. Wires. 1999. Caspian Tern (Hydroprogne caspia), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/403
- Stokes, D.W. and L.Q. Stokes. 1996. Stokes Field Guide to Birds Eastern Region. 1st ed. NewYork: Little, Brown, and Company. Print.
Edited by Stephanie Egger in 2011.
Species: H. caspia
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