Gull-billed Tern

Gelochelidon nilotica

U.S. Fish & Wildlife Service
  • LARIDAE
  • Gulls, Terns, and Skimmers
  • Charadriiformes
  • Charrán pico grueso, Pico de gaviota, Golondrina playera
  • Sterne hansel
Introduction
The Gull-billed Tern is a medium-sized, heavy-billed tern with a broad distribution, and notably varied diet. Watch for this uncommon tern flying into the wind over marshlands, catching flying insects in the air, plucking prey from the ground or water surface, or nesting among other terns and seabirds.
Appearance Description
These medium-sized terns weigh about 6 ounces (170 grams), and measure about 14 inches in length, with a wingspan of 35 inches. Both sexes look alike, with a stocky, pale gray body; wide, black-tipped wings; long black legs; a short notched tail; and a stout black bill. Unlike many terns, Gull-billed Terns have a black cap only when breeding; during winter the head is nearly white, with a dark smudge behind the eyes. They are sometimes confused with Sandwich Terns, which have a thinner black, pale tipped bill, and thinner wings.
Range Map
Courtesy of Kenn Kaufman
Range Distribution
Gull-billed Terns breed along the Atlantic Coast from New Jersey to Florida, along the Gulf Coast from Florida to Mexico, and locally in southern California near the Salton Sea. They also breed in warmer scattered sites across Eurasia, northwestern Africa, and Australia. They winter in the Gulf Coast and points south. 
 

A legend for the range map to the right can be found
here.
Habitat
Gull-billed Terns forage over marshes, pastures, farms, and other open coastal areas. They nest and breed on gravelly or sandy beaches and islands, and winters in salt marshes, estuaries, lagoons, and plowed fields; less frequently along fresh-water areas.
Feeding
Unlike most terns, Gull-billed Terns have a broad diet; they neither depend on fish, nor plunge-dive for it. Instead they commonly feed on insects, small crabs, lizards, and other prey snatched from the ground, air, or vegetation. The species is also known to eat other tern chicks, and will steal fish from other terns in mixed nesting colonies.
Reproduction
Gull-billed Terns generally nest and breed in small, loosely packed colonies. Most courtship posturing, and feeding displays are performed on the ground. Their nests are shallow depressions on open ground, occasionally rimmed with soil or vegetation. Gull-billed Terns lay average of 3, but up to 7 pale buff eggs, spotted with brown. Both sexes build nests, incubate the eggs, and care for the young. Incubation lasts slightly over 3 weeks. The downy chicks are born able to walk, with their eyes open. They may leave the nest, moving to denser plant cover nearby, only a few days after hatching. They begin to fly at 4 to 5 weeks of age, and may remain with their parents for 3 months.
Migration
Gull billed terns are mainly summer residents in the U.S.; some remain throughout the winter on the Gulf of Mexico coast.
  • 195,000
  • 10,000-25,000
  • moderate population declines, small population size
Population Status Trends
Gull-billed Terns are less numerous today on the Atlantic coast than at their historical levels, prior to the millinery trade in the late 1800s. Populations, while generally stable, are locally erratic, so determining trends is difficult. The species is a former USFWS Bird of Conservation Concern, and a continentally threatened species. Gull-billed Terns colonies moved north from Mexico to California beginning in the 1920s, but the Salton Sea population has declined significantly; they are listed as a "species of special concern" in that state.
Conservation Issues
Gull-billed Tern populations, although partially recovered from the effects of hunting during the millinery trade period in early 1900s, are today limited by the availability of suitable undisturbed habitat and winter food, flooding, predation, and human disturbance. In addition, many Gull-billed Tern colony sites have been taken over since the early 1970s by Herring and Black-backed Gulls. The species is also vulnerable to eggshell thinning and reproductive failure from pollution and pesticide contamination.
 
These terns seem both less tolerant of disturbance and less faithful to nest sites than most other tern species. Some former nesting areas in salt marshes have been abandoned, possibly due to human encroachment. Some terns have adapted by nesting on Gulf Coast rooftops. Human disturbance from boating, recreation, and development is a primary conservation concern, as it causes the young to disperse from the nest too early, sometimes resulting in heavy losses due to exposure to weather and predators. Where human activities are concentrated on some Atlantic Coast barrier islands, this species has shifted to nesting on marshes and dredge spoil islands. The ability to switch colony sites in the face of disturbance may have allowed this tern species to fare better than others. Protection of both active and potential colony sites is an important management tactic, as initially unused sites may be used later on, either in the same season, or the following year.
What You Can Do
Never leave fishing lines, lures, or hooks on beaches; entanglement is usually lethal to terns.
 
Don't dump garbage or fishing bait which feeds competing and 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.
 
For actions you can take, including Audubon activities, please visit our resources page.
More Information
Learn about ocean conservation at: http://www.livingoceans.org/index.shtml
 
Visit our resources page for more information about this species.
Natural History References
Parnell, J. F., R. M. Erwin, and K. C. Molina. 1995. Gull-billed Tern (Sterna nilotica). In The Birds of North America, No. 140 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia and The American Ornithologists' Union, Washington, D.C.
 
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
 
Conservation Status References
Parnell, J. F., R. M. Erwin, and K. C. Molina. 1995. Gull-billed Tern (Sterna nilotica). In The Birds of North America, No. 140 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia and The American Ornithologists' Union, Washington, D.C.
 
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