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Roseate Tern Life History

Habitat

Habitat Shorelines

Roseate Terns in eastern North America nest on sandy barrier islands, on rocky islands, and occasionally on islands or hummocks in saltmarshes. Typically, colonies in the Northeast include Common Terns and are near productive foraging areas such as shoals, tidal rips, and sandbars. They set their nests among rocks, shells, or vegetation, often in concealed spots such as clumps of seaside goldenrod or beach grass. In the Florida Keys, some Roseate Terns nest on flat gravel rooftops among Least Terns, while those offshore in the Gulf of Mexico at the Dry Tortugas nest in Sooty Tern colonies. In the Caribbean, they sometimes nest on low coral islets or on shallow cliffs on limestone stacks, often among Bridled Terns or Sandwich Terns. Roseate Terns migrate well offshore, usually out of sight of land. Open beaches and coastal inlets produce the most reports of migrants, both in spring and fall. Offshore, migrants sometimes feed with other seabirds above foraging tuna, which drive small fish toward the surface, or along strong temperature breaks (thermoclines) where two ocean currents meet, where prey are also concentrated, such as along the Gulf Stream boundary. Their habitats and habits in the Caribbean and South America during the nonbreeding season are not well known. Most forage over the open ocean, where some also rest and even spend the night, whereas others return to ocean beaches, rivermouths, and estuaries to roost at night.

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Food

Food Fish

Roseate Terns eat small fish, which they capture either by plunging into the water or by swooping down to dip prey from the surface. They occasionally also eat insects, squid, and crustaceans. They forage from close to shore, near beaches and rivermouths, out to pelagic (deep water) zones, sometimes in association with other terns, noddies, and shearwaters. Nesting birds tend to hunt closer to shore, where they sometimes forage with cormorants, loons, pelicans, and alcids or hunt over feeding schools of predatory fish such as bluefish. In the northwestern Atlantic, they feed their young American sandlance. Wintering birds in Puerto Rico eat mostly anchovies and herring, often along the edges of offshore reefs. Many Roseate Terns steal fish from Common Terns or even Atlantic Puffins that are returning to colonies to feed their young. Known prey species include American sandlance, bay anchovy, striped anchovy, Atlantic herring, dwarf herring, blueback herring, Atlantic menhaden, round herring, Atlantic mackerel, Atlantic silversides, reef silversides, bluefish, pollock, butterfish, white hake, and fourbeard rockling. They rarely eat small crustaceans such as shrimps, prawns, euphausiids, and amphipods.

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Nesting

Nest Placement

Nest Ground

Male and female (or pairs or trios of females) investigate potential nest sites together, selecting a site on the ground near vegetation or a prominence in the landscape. In the Caribbean, some birds nest on cliffs or ledges on limestone islets. From New York to New England, most Roseate Terns nest in artificial nest boxes provided by conservationists.

Nest Description

Nests are simple scrapes in the ground, ranging from 2.4 to about 4.8 inches in diameter. These scrapes are unlined at first, but while incubating and brooding, the adults often add bits of shell, rock, or vegetation to the scrape over a period of several weeks.

Nesting Facts

Clutch Size:1-5 eggs
Egg Description:

Brown with dark speckles and streaks.

Condition at Hatching:

Downy, eyes open, able to walk but stays in nest.

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Behavior

Behavior Aerial Dive (water)

In many colonies, Roseate Terns begin courtship displays within a few days of returning to their breeding areas, though some pairs do not move to the actual nest location for several more weeks. Males, especially those without mates, fly around colonies calling and showing a small fish in the bill. Females follow or watch; the male then lands to present the fish in a contorted courtship posture, with his very long tail raised. The most memorable of the courtship displays is called High Flight, where a courting pair rapidly flies together, upwards to a great height (over 1,000 feet on occasion). The male then begins a downward glide on bent wings, pointing his bill earthward, as the female glides ahead of and just above him, sweeping her head and neck from side to side as the two descend. Up to six additional terns may accompany the pair as they begin their display, and some nonbreeding birds may continue to display for several months, perhaps in practice for future breeding. As with other tern species, male Roseates feed their mate in ritualized courtship feeding displays, both at display sites and at the nest, at least until eggs are laid. Males are aggressive toward other males, often chasing them away from the immediate nest area or confronting them with a threat display in which they raise crown feathers and pump the head up and down, giving harsh calls. Roseate Terns appear to be monogamous. Some pairs stay together for up to 12 years, but most pairs do not partner for more than two breeding seasons. Many colonies of Roseate Terns have more females than males (up to a ratio of 1 male:1.3 females), some nests are tended by two or even three females (and no males). Female-female pairs may stay together for at least 5 consecutive years. All parents associated with a nest incubate eggs and defend chicks equally.

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Conservation

Conservation Declining

Roseate Tern populations have been in decline for more than a century. Partners in Flight estimates a global breeding population of 160,000 birds. (An estimated 6,400 breed in the U.S., with as many as 14,000 estimated to breed in the Caribbean.) Partners in Flight rates the species a 15 out of 20 on the Continental Concern Score, and includes the species on the Yellow Watch List for species with declining populations. Most of the North American population nests between Long Island, New York, and Cape Cod, Massachusetts. The species is listed as Endangered in Canada. The U.S. Fish and Wildlife Service lists the species as Endangered from Maine south to North Carolina. Populations in Florida, Puerto Rico, and the Virgin islands are federally listed as Threatened. No breeding populations currently exist in Virginia and North Carolina. This species continues to be targeted by hunters in Africa and South America, and their eggs are harvested from colonies in the Caribbean. Marine pollution, including oil spills and toxic chemicals such as pesticides, has been implicated in population losses in the past and continues to be a threat. Human disturbance of colonies has led to abandonment of formerly productive nesting sites. Many of their breeding islands, from New England to the Caribbean, have lost habitat to erosion and rising sea levels, and some breeding islands have vanished as recently as 2000; that process is forecast to continue and accelerate. Colonies in New England receive intensive management to help safeguard breeding success. Measures include erosion control; artificial nesting sites such as boxes, tires, and elevated boards; management of invasive plants to keep nesting areas from becoming overgrown; and managing or removing large gulls, which can steal eggs and chicks from nests.

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Credits

Crossley, R. (2011). The Crossley ID guide: Eastern birds. Princeton: Princeton University Press.

Dunne, P. (2006). Pete Dunne's essential field guide companion. Houghton Mifflin Harcourt, New York, USA.

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. (2019). Longevity records of North American birds. Version 1019 Patuxent Wildlife Research Center, Bird Banding Laboratory 2019.

Nisbet, Ian C. T., Michael Gochfeld and Joanna Burger. (2014). Roseate Tern (Sterna dougallii), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

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

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