The Sandwich tern (Thalasseus sandvicensis) is a tern in the family Laridae. It is very closely related to the lesser crested tern (T. bengalensis), Chinese crested tern (T. bernsteini), Cabot's tern (T. acuflavidus), and elegant tern (T. elegans) and has been known to interbreed with the lesser crested. It breeds in the Palearctic from Europe to the Caspian Sea wintering to South Africa, India and Sri Lanka.
The Sandwich Tern occurs through the tropical, subtropical, and temperate coastal regions of the Atlantic Ocean (Raffaele and others 1998). In Puerto Rico, it can be seen throughout the year, but it is most abundant from September to November and from March to May (Biaggi 1997). It nests on and around Culebra and some islets off Guayanilla and La Parguera in the municipality of Lajas, while it is a regular visitor during the winter in the San Juan harbor and the bays of Boquerón and Mayagüez (Kepler and Kepler 1978, Oberle 2018). It is also present on Vieques, where it is considered a rare visitor in summer and fall, and extremely rare in spring (Gemmill 2015). It usually inhabits coastal areas, harbors, and lagoons (Raffaele and others 1998). The atlas fieldwork yielded a total of 76 records within 55 hexagons or 11 percent of the 479 total hexagons (see map). Of the 55 hexagons where this species was found, breeding met the atlas definition of confirmed in 5 percent (3) of the hexagons, while this species was observed in 95 percent (52) of the hexagons but without evidence of breeding (see map).Sandwich Tern distribution. The map shows the highest breeding code by hexagon and overlaying the ecological life zones in Puerto Rico. Note: percentages may not total 100 due to rounding. 127Sandwich Tern/Charrán Piquiagudo
Previously published reports indicate that the Sandwich Tern breeds from May to July (Raffaele and others 1998). A simple scrape nest is made on a sand bar or in coral rubble (Raffaele and others 1998). Atlas results confirm that this species breeds in June and that the breeding activity takes place in the subtropical dry forest life zone (see chart). Results show that this species breeds in coastal areas within the subtropical dry forest life zone (100 percent of the hexagons) (see table and map).
The current overall population trend of the Sandwich Tern is fl uctuating, although some of the populations are stable and others have unknown trends (Wetlands International 2012). This species is currently listed as a species of least concern by the IUCN (BirdLife International 2018). Locally, this species is not listed in any of the threatened categories of PRDNER and USFWS. In Puerto Rico, the Sandwich Tern has a protected habitat in land of 3 percent or 2 km2 of the total area covered by the hexagons where evidence of breeding was found for this species (72 km2).