San Diego Management & Monitoring Program


Elegant tern
Thalesseus elegans


Kingdom Phylum Subphylum Class Order Suborder Family

Current distribution rangewide

Breeds primarily in Mexico along the coast of Baja California and more prominently in the Gulf of California on Isla Rasa Island [1]. Populations have also been documented breeding along the coast of San Diego County and as far north as Los Angeles Harbor [1]. Will migrate north around the first week in October, rarely migrating north of Marin County.


Known Populations in San Diego County

Elegant tern occurs in MUs 1, 2, 6, and 7 in the MSPA.


List status

Not listed


Habitat affinities

Preferred habitats are inshore coastal waters, bays, estuaries, and harbors [3]. Rarely occurs far offshore, but will occasionally. Never occurs inland [3]. Breeds on low, flat, sandy islands [4]. Commonly congregates along beaches and tide flats when not feeding. Will usually avoid mingling with its own species when present.


Taxonomy and genetics

The elegant tern (Thalasseus elegans) was formerly classified in the genus Sterna [5]. Related to and grouped with crested terns - Elegant, Royal (Thalasseus maximus), Great Crested (T. bergii), Sandwich (T. sandvicensis), Lesser Crested (T. bengalensis), and Chinese Crested (T. bernsteini) terns.


Seasonal activity

Breeds from San Diego Bay south to central Baja California and most common on Isla Rasa located in the Gulf of California [7]. Post-breeders in summer occur regularly on the Pacific Coast from central California to Costa Rica. Frequents the coasts of Central and South America in winter [7].


Life history/ reproduction

Elegant terns will arrive to their nesting sites along San Diego Bay around the second week in March, much earlier than post-nesting visitors [3]. At San Diego Bay, typically nests on bare ground. Does not use same nest site from year to year [7].Will use debris such as twigs, bones, feathers, and clam and snail shells. From a distance individual nests are difficult to locate because feces splattered around them match substrate color [8].Clutch size is generally 1, but can be 2. Eggs are white to pink buff, marked with black or dark brown. Most eggs are laid in April. Incubation period is about 20-30 days and carried out by both parents [9].


Diet and foraging

Primarily feeds in shallow ocean waters, but may also forage in protected bays and lagoons, rarely freshwater [4]. Hovers over water and dives for small fish. Transports single fish crosswise in bill. Major prey species come from five families of fish: Engraulidae (anchovies), Clupeidae (sardines), Atherinidae (silversides), Gobiidae (gobies), and Scombridae (mackerels). Interannual variation. Primary prey is northern anchovy.


Threats

Threats to tern colonies include predation, human disturbance, and urban development [10]. Other threats to terns are food shortage influenced by over-fishing and environmental contamination.


Elegant tern sources