Sandwich Tern Life History

Habitat

Sandwich Terns nest on sandy barrier beaches and barrier islands close to the ocean, including low-lying dredge-spoil islands. They usually avoid areas with dense vegetation. They nest less often on rocky substrates, except in the Caribbean where they use low coral islands (cays). While nesting, they forage mostly near shore, in shallow ocean waters. During migration and in winter, Sandwich Terns stay in the same kinds of coastal and island habitats, resting and roosting on beaches as well as human-made structures such as piers, jetties, and pilings. They forage close to shore in shallow ocean waters as well as in rivermouths, estuaries, lagoons, and inlets. They seldom forage far inland or far out to sea in North America. Many records of this species well inland in North America are associated with the passage of hurricanes and tropical storms.

Food

Sandwich Terns eat mostly small schooling fish, as well as squid, shrimp, crustaceans, and insects. They capture prey by plunge-diving from the air into the sea, grasping the prey in the bill. They usually dive from heights of 25 feet or less. Normally, only a few Sandwich Terns feed near one another, although hundreds may gather when prey are abundant and concentrated. At such times they often join with other seabird species to feed in dense flocks. In some places, prey may be concentrated by strong currents or by the actions of larger, predatory fish. On occasion, Sandwich Terns follow trawlers to take small fish or shrimp brought to the surface. They've even been seen following a farmer's plow, capturing flying insects disturbed by the activity. Prey items include lesser sand eel, northern sandlance, Atlantic menhaden, Gulf menhaden, Atlantic croaker, dwarf herring, Atlantic thread herring, bluefish, butterfish, weakfish, star drum, silversides, many species of anchovy and flying fish, jacks, parrotfish, tuna, and mackerel. Insect prey include mayflies and flying ants.

Nesting

Nest Placement

Male and female choose the nest site together, on sandy or shelly areas with little or no vegetation, on barrier islands, beaches, or dredge-spoil islands.

Nest Description

Nests are natural depressions or scrapes in the sand that the adults dig with their feet. They sometimes add shells or other adornments gathered from the wrack line during nesting. Nests average about 6 inches across and 1.3 inches deep.

Nesting Facts

Behavior

Sandwich Terns nest in dense colonies. Many probably perform courtship and form pair bonds before they arrive at the nesting colony, while others associate in “clubs,” small flocks of mainly unpaired birds that gather on the periphery of the colony and socialize. Once paired, Sandwich Terns begin courtship activities in earnest. Usually courtship commences on land and proceeds into the air. Males arrive at rest sites with a fish, calling and flying around, then landing to show off the fish. An interested female lowers her head, soliciting food as a chick would, and the male may then present her with a small fish, dropping the wings and raising the crest as he vocalizes—or he may fly off, inviting the female to court in the air. When the pair performs in the air together, they rise quickly in a circle together for several minutes, then begin a rapid descent in tandem, gliding downward and calling, with one bird (probably the male) often raising the wings high over the body on the way down.

Sandwich Tern pairs defend a small area around the nest and their chick, not more than 2 feet from the nest. Males sometimes make threat displays at other males that approach too closely, warning them away with calls, raised crests, drooped wings, and rapid head movements. Physical conflict is rare in this relatively peaceful species. Sandwich Terns are mostly monogamous in their mating system, but paired males sometimes attempt to mate with additional females. Some birds pair with the same partner for as many as 4 consecutive nesting seasons. Both parents incubate the egg and feed the chick (sometimes two, usually one). As the chicks become mobile just a few days after hatching, the adults gather them into a crèche (a tight group) but can always recognize (and feed) their own chick in these groups. The parents continue to feed their chick well after it fledges, and family groups remain together for 6 months or more after hatching. In the nonbreeding season, Sandwich Terns are gregarious and often roost and feed among other seabirds, especially terns and gulls.

Conservation

Sandwich Terns are relatively widespread and common, but trends are difficult to measure because colony locations often change. Their North American range has expanded slightly northward in recent years and some local populations have shown small increases. Partners in Flight estimates a global breeding population of 1 million (with an estimated 94,000 breeding in the U.S.). They rate the species a 10 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Sandwich Tern populations experienced major declines during the nineteenth century, due mostly to the millinery trade and egg collecting. Some shooting and egg collecting continues, but the major conservation challenges for this species are the degradation or loss of breeding habitats from both development and climate change, which causes erosion, sea-level rise, and storm damage. Disturbance at nesting colonies by humans and dogs can cause nest abandonment. Fortunately, this species responds readily to the creation of artificial nesting habitat such as dredge-spoil islands.

Credits

Kushlan, J. A., M. J. Steinkamp, K. C. Parsons, J. Capp, M. A. Cruz, M. Coulter, I. Davidson, L. Dickson, N. Edelson, R. Elliott, R. M. Erwin, S. Hatch, S. Kress, R. Milko, S. Miller, K. Mills, R. Paul, R. Phillips, J. E. Saliva, W. Sydeman, J. Trapp, J. Wheeler and K. Wohl (2002). Waterbird conservation for the Americas: The North American waterbird conservation plan, version 1. Washington, DC, USA.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Shealer, David, Jeff S. Liechty, Aaron R. Pierce, Peter Pyle and Michael A. Patten. (2016). Sandwich Tern (Thalasseus sandvicensis), version 3.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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