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Roseate Tern
Sterna dougallii
Order
CHARADRIIFORMES
– Family
LARIDAE
Authors: Gochfeld, Michael, Joanna Burger, and Ian C. Nisbet
Revisors: Nisbet, Ian C.

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Introduction

Adult Roseate Tern in flight; Bird Island, MA; May.
Figure 1. Breeding range of the Roseate Tern in the Northeastern U.S. and Canada.
Figure 2. Breeding range of the Roseate Tern in the Caribbean region, including the Florida Keys and the Bahamas and Turks and Caicos Islands.
Figure 3. Distribution of Roseate Tern in North and Central America.

Many consider the Roseate Tern to be the most beautiful of all terns. It is whiter than other medium-sized terns, with a long jet-black cap and a delicate pink ‘bloom’ on the breast; its long white tail streamers flutter as it flies and are raised prominently in some of its displays. Arthur Cleveland Bent wrote in his Life Histories of North American Gulls and Terns (1921: 256) about his experience of collecting his first specimen: “I shall never forget the thrill of pleasure I experienced when I held in my hand, for the first time a Roseate Tern and admired with deepest reverence the delicate refinement of one of nature’s loveliest productions.”

Nowadays most of us prefer to observe and appreciate the bird in life, but this is not always easy. The Roseate Tern is rare and is not often seen away from its breeding sites, most of which are on small islands off-limits to visitors. The best places to see it in North America are beaches and islands around Cape Cod, Massachusetts, where it gathers in flocks during the post-breeding period in July–September. Even at the breeding sites in spring, the pink color that gives the species its name is difficult to see because it fades quickly in sunlight. Although the feathers remain pink at the base, this is covered by white feather tips that reflect bright light. However, in diffuse lighting the pink color sometimes shows through the white covering layer as a delicate shell pink or peachy bloom on the underparts.

The Roseate Tern is similar in size to the Common (Sterna hirundo), Arctic (S. paradisaea) and Forster’s terns (S. forsteri) and is grouped with them as part of the group of ‘typical black-capped terns’ of the genus Sterna. However, in many aspects of its morphology, ecology and behavior, it appears closer to the ‘crested’ terns of the genus Thalasseus, especially the Elegant (T. elegans), Sandwich (T. sandvicensis) and Cabot’s (T. acuflavidus) Terns. These features include the ‘spiky’ down of its newly-hatched chicks, its grating flight calls and its ‘gakkering’ threat display, which is characteristic of the ‘crested’ terns and is performed by no others. The Elegant and Sandwich Terns are also similar in displaying the ephemeral pink ‘blush’ on the underparts in fresh plumage. However, genetic studies indicate that the Roseate is only distantly related to the ‘crested’ terns—an enigma that remains to be resolved.

Like most of the ‘crested’ terns, the Roseate Tern is primarily tropical and subtropical in distribution, with many breeding colonies on islands scattered through the Indian and w. Pacific Oceans and the Caribbean Sea, including the Florida Keys. However, it also has several discrete breeding populations at temperate latitudes, including three in the North Atlantic Ocean: in the ne. USA and se. Canada (41–48° N), the Azores archipelago (37–40° N) and nw. Europe (48–56° N). The North Atlantic and Caribbean populations are all small and threatened, and those in the Northeastern USA and nw. Europe have been intensively studied in recent decades. These are all considered to belong to the same subspecies, but the Northeastern and Caribbean populations differ in several characteristics, including size and bill color. They also differ in several aspects of breeding biology, including clutch-size: most northeastern birds are similar to the temperate Sandwich Tern in laying clutches of two eggs, whereas most Caribbean birds are more similar to the tropical/subtropical Cabot’s Tern and lay single eggs. Birds from both populations winter on the north and east coasts of South America, but they have proved difficult to locate and study there. Although several roost sites have been discovered along the coast, the birds appear to spend most of their time foraging at sea.

The Roseate Tern is exclusively marine and is a specialized plunge-diver, feeding on small schooling fish. It usually forages over reefs, sandbars or tide rips, or in association with predatory fish that force smaller fish to the surface. Adapted for fast flight and deep diving, it usually submerges completely when diving for fish. Its aerial courtship flights are among the most spectacular of any seabird.

Northeastern and European individuals invariably breed in mixed colonies with Common or Arctic Terns. Like those of other terns, Roseate Tern colonies suffered encroachment from expanding gull populations in the middle third of the 20th century, but this has been reversed in recent decades and most breeding sites are now secure. In most Northeastern colonies, Roseate Terns nest under cover such as dense vegetation or rocks, and they readily adapt to nesting in artificial structures such as wooden nest boxes, allowing them to keep their eggs and chicks well hidden. At most Caribbean colonies, they nest much more in the open. In Florida, they nest with Least Terns (Sternula antillarum) and elsewhere in the Caribbean generally with Bridled (Onychoprion anaethetus), Sooty (O. fuscata), and/or Cabot’s Terns. The total breeding population in eastern North America is currently (2013) about 3,200 pairs; more than 90% of the total nest on three islands in eastern New York and Massachusetts (Appendix 1). The Caribbean population is difficult to enumerate because of frequent movements of birds from site to site and because many colonies are scattered on small islets, particularly in the Bahamas and Virgin Islands, but recent population surveys suggest a total of about 6,000 pairs (Appendix 2).

The Canadian Wildlife Service lists this species as Endangered, while the U.S. Fish and Wildlife Service lists the Northeastern population as Endangered and the Caribbean population as Threatened. Most of the breeding sites in the northeast USA and Canada are intensively managed, with control of predators and encroaching gulls, and often with management or restoration of vegetation and other habitats. Since 1987, intensive studies have been conducted at all the major breeding sites and many minor sites, including a ‘Metapopulation Study’ involving large-scale banding, retrapping and resighting. Information on the Caribbean population comes mostly from Culebra and islets off La Parguera, Puerto Rico. A comprehensive review of all information on North American and Caribbean Roseate Terns relevant to management was published by the U.S. Fish and Wildlife Service (2010).

The Northeastern population of Roseate Terns falls into two groups with somewhat different ecology: a ‘warm-water’ group in the area between eastern Long Island, NY, and Cape Cod, MA, and a ‘cold-water’ group from the outer shore of Cape Cod through the Gulf of Maine to Nova Scotia and New Brunswick. The ‘warm-water’ group includes about 90% of the total population and is now concentrated into three major colonies that have been intensively studied. The ‘cold-water’ group includes about 10% of the total population and is scattered among about 16 smaller colonies; these have been well monitored in recent years but few intensive studies have been conducted (Appendix 1). The birds move fairly freely among sites within each of the two groups, but there appears to be less frequent interchange of individual birds between the two groups (Spendelow et al. 2010).

In this account, references to named individuals without dates indicate unpublished data supplied in personal communications; ICTN indicates unpublished data of the author.