The royal tern (Thalasseus maximus) is a tern in the family Laridae. The species is endemic to the Americas, though strays have been identified in Europe. Adult royal tern and sandwich tern (right) in flight at Core Banks, North Carolina.
The royal tern has few predators when it is mature, but before the chicks hatch or while they are chicks the tern is threatened by humans, other animals, and the tides. Humans threaten terns by fishing and by disrupting the tern nesting sites. Fishing nets can catch a tern while it is diving, making it unable to feed or it may cause it to drown if it is caught under water. Animals such as foxes, raccoon, and large gulls prey on tern chicks and tern eggs.
The Royal Tern occurs on the western coast of Africa (Biaggi 1997, Oberle 2018, Raffaele and others 1998) and from the Southern United States through much of coastal South America including the West Indies (Raffaele and others 1998). In Puerto Rico, it is a common visitor during winter in the San Juan Harbor, Laguna San José, Laguna Torrecilla, Boquerón Bay, and Mayagüez (Oberle 2018). On Vieques, it is considered a common non-breeder in all seasons (Gemmill 2015). It has been known to nest on Mona (McCandless 1958) and cays near Culebra (Kepler and Kepler 1978, Oberle 2018). It usually inhabits coastal marine waters (Oberle 2018), harbors, and lagoons (Raffaele and others 1998). The atlas fieldwork yielded a total of 134 records within 82 hexagons or 17 percent of the 479 total hexagons (see map). Of the 82 hexagons where the Royal Tern was found, breeding met the atlas definition of confirmed in 4 percent (3) of the hexagons and probable in 1 percent (1), while the species was observed in 95 percent (78) of the hexagons but without evidence of breeding (see map). Royal 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. 125Royal Tern/Charrán Real
Previously published reports indicate that the Royal Tern breeds from April to July but is irregular as to number of pairs and location (Raffaele and others 1998). Nesting is generally colonial and on small cays, and the nest consists of a scrape made on a sandy beach or in a rocky depression (Oberle 2018, Raffaele and others 1998). Atlas results show that this species breeds during May and June (see chart). Overall, the breeding activity peaks in June, and it mostly takes place within the subtropical dry forest life zone (see chart). Results show that this species breeds in coastal areas mostly within the subtropical dry forest life zone (75 percent of the hexagons) (see table), but it also breeds within the subtropical moist forest life zone (25 percent of the hexagons) (see table and map).
The current overall population trend of the Royal Tern is described as stable, although some populations have unknown trends (Wetlands International 2012), and it is currently listed as a species of least concern by the IUCN (BirdLife International 2018). In Puerto Rico, Oberle (2018) noted that the only confirmed breeding sites for Royal Terns were on cays off Culebra, but that breeding on these sites was reduced since 1988 to just a sporadic handful of breeding pairs. Locally, this species is not listed in any of the threatened categories of PRDNER and USFWS.In Puerto Rico, the Royal Tern has a protected habitat in land of 3 percent or 3 km2 of the total area covered by the hexagons where evidence of breeding was found for this species (95 km2).