Caspian Tern

Hydroprogne caspia

(c) Glen Tepke
  • LARIDAE
  • Gulls, Terns, and Skimmers
  • Charadriiformes
  • Charrán caspia
  • Sterne caspienne
Introduction
With a soaring flight, and body size similar to a mid-sized gull, the Caspian Tern is the largest tern in the world. Its large, bright red bill and harsh call make it recognizable as it scouts for fish above the water, or struts along sandbars, often trailed by older youngsters.
(c) Charles Bush
Appearance Description
This large tern weighs about 1.4 pounds (660 grams), and measures about 21 inches in length, with a wingspan of 50 inches. Sexes look similar, with a heavy, grayish-white body, black cap, shallowly forked tail, black legs, and a large red bill.
Range Map
Courtesy of Kenn Kaufman
Range Distribution
Caspian Terns are found on all continents but Antarctica. They breed in scattered locations across North America, along the coasts of the Pacific, Atlantic, and Gulf of Mexico, and inland in the western  United States, central Canada, and along the Great Lakes. Caspian Terns from North America winter along the southern portions of the Atlantic and Pacific coasts and the Gulf Coast, to northern South America.
 
A legend for the range map to the right can be found here.
Habitat
Caspian Terns are locally common along both coasts and inland, primarily around large lakes and bays. They favor protected areas in a variety of fresh- and salt-water habitats. Flat rocky islands, sandy beaches, and other driftwood-strewn, sparsely vegetated, open ground areas are typical breeding habitat.
Feeding
Caspian Terns live almost entirely on fish, often concentrating on a few abundant fish species in a given area. They scout about 10 yards above the water with a powerful, steady flight, the bill typically pointing downward. Upon spotting a fish, the tern hovers, then plunges, usually submerging completely in shallow surface waters to capture its prey. Caspian Terns sometimes steal food from other birds, and occasionally eat the eggs and young of other birds.
Reproduction
Caspian Terns nest and breed in scattered colonies. Starting at 3-5 years of age, the terns begin performing courtship feeding on the ground, and aggressively defend breeding territories. Tern nests range from shallow scrapes in bare sand or gravel, to rimmed depressions lined with shells or vegetation.
 
Caspian Terns usually lay 1-3 pale buff eggs, marked with dark blotches. Both sexes incubate eggs and care for young. The downy chicks hatch after a little over  3 weeks of incubation, and are soon able to walk, with their eyes open. If undisturbed, they may remain in or near the nest until they begin to fly, at about 6 weeks of age. The young are noted for receiving  extended parental care after leaving the nesting colony, sometimes remaining with parents for up to 8 months.
Migration
Both inland and coastal breeders migrate southward and to coastal areas each winter.
  • 250,000
  • 100,000
  • small population size, otherwise no conservation concern
Population Status Trends
Caspian Tern populations are stable or increasing across most of North America; recently their breeding range has expanded to southern Alaska. Breeding Bird Survey (BBS) data shows increases in some populations. However, Caspian Terns are decreasing in Eurasia and Africa, and are listed as vulnerable, rare, or even extinct in parts of their former range, due in part to the scattered nature of their breeding colonies.
Conservation Issues
Protection of Caspian Terns and their traditional nesting sites (bare sand substrate on islands free of mammalian predators) have succeeded in stabilizing populations in most parts of their North American range. The terns have also benefited from their ability to make use of human-created dikes and dredge spoil islands for breeding. In most regions of North America, however, the number and size of Caspian Tern colonies appears to be limited by suitable available nesting habitat.
 
Erosion of nesting islands, changing water levels, gull predation on eggs and young, and harassment by predators and humans all reduce nesting success.  Breeding colonies that are not situated on islands are especially vulnerable to disturbance and predation; Caspian Terns readily desert their colonies if disturbed by mammalian predators, including humans, early in the breeding season.
 
 In the Columbia River estuary, near the Washington-Oregon border, the world's  largest colony of Caspian Terns was feeding upon juvenile salmon and was causing conflicts with efforts to restore threatened salmon runs. During 1999-2001, the entire colony was successfully relocated to an island 16 miles closer to the ocean, using a combination of vegetation management, decoys, and recorded tern vocalizations. In this same area, Bald Eagles that flush nesting terns, and hybrid Western/Glaucous-winged Gulls that eat tern eggs and chicks, pose additional challenges.
 
In North America, studies including nesting, feeding, breeding, parental behavior, courtship, and nest site selection of Caspian Terns have been conducted along the Great Lakes and the Pacific and Gulf coasts. Band recovery data have revealed information on the migration patterns and over-wintering sites of these populations.
What You Can Do
Never leave fishing lines, lures, or hooks on beaches; entanglement kills numerous terns each year.
 
Don't dump garbage or fishing bait which feeds predatory gulls.
  
Don't disturb nesting tern colonies when hiking or landing boats; prevent dogs and children from disturbing them. When parent terns abandon their nests, eggs or chicks can overheat or become wet and chilled, often resulting in death.
 
Make environmentally-friendly seafood choices, which helps protect the fish that Caspian Terns and many other seabirds depend upon. Learn more at http://seafood.audubon.org/
 
 Report sightings of color-banded Caspian Terns in the western U.S., Canada, and Mexico at: http://www.columbiabirdresearch.org/
 
 
For actions you can take, including Audubon activities, please visit our resources page.
More Information
Learn about research involving Caspian Terns on the Columbia River: http://www.columbiabirdresearch.org/
 
 
Visit our resources page for more information about this species.
Natural History References
Cuthbert, F. J., and L. R. Wires. 1999. Caspian Tern (Sterna caspia). In The Birds of North America, No. 403 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
 
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, Inc., New York, 2000
 
Kaufman, Kenn. Lives of North American Birds. Houghton Mifflin Company, New York, 1996
Columbia Bird Research. 2006. Caspian Tern Research on the Lower Columbia River: 2005 Draft Season Summary. Real Time Research,Inc. Bend, Oregon. On-line: http://columbiabirdresearch.org/.
Conservation Status References
Cuthbert, F. J., and L. R. Wires. 1999. Caspian Tern (Sterna caspia). In The Birds of North America, No. 403 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
 
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, Inc., New York, 2000
 
Kaufman, Kenn. Lives of North American Birds. Houghton Mifflin Company, New York, 1996
Columbia Bird Research. 2006. Caspian Tern Research on the Lower Columbia River: 2005 Draft Season Summary. Real Time Research,Inc. Bend, Oregon. On-line: http://columbiabirdresearch.org/.