Sternula antillarum
Silhouette: Sheatherius · PhyloPic
In 3 days <5% in a week ~10%
The least tern (Sternula antillarum) is a species of tern that breeds in North America and locally in northern South America. It is closely related to, and was formerly often considered conspecific with, the little tern of the Old World. Other close relatives include the yellow-billed tern and Peruvian tern, both from South America.
It is a small tern, 22–24 cm (8.7–9.4 in) long, with a wingspan of 50 cm (20 in), and weighing 39–52 g (1.4–1.8 oz). The upper parts are a fairly uniform pale gray, and the underparts white. The head is white, with a black cap and line through the eye to the base of the bill, and a small white forehead patch above the bill; in winter, the white forehead is more extensive, with a smaller and less sharply defined black cap. The bill is yellow with a small black tip in summer, all blackish in winter. The legs are yellowish. The wings are mostly pale gray, but with conspicuous black markings on their outermost primaries. It flies over water with fast, jerky wingbeats and a distinctive hunchback appearance, with the bill pointing slightly downward.
It is migratory, wintering in Central America, the Caribbean and northern South America. Many spend their whole first year in their wintering area. It has occurred as a vagrant to Europe, with one record in Great Britain and one in Ireland.
It differs from the little tern mainly in that its rump and tail are gray, not white, and it has a different, more squeaking call; from the yellow-billed tern in being paler gray above and having a black tip to the bill; and from the Peruvian tern in being paler gray above and white (not pale gray) below and having a shorter black tip to the bill. Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Padre Island National Seashore | 🇺🇸 United States | |
| 2 | Jaragua National Park | 🇩🇴 Dominican Republic | |
| 3 | Ría Lagartos Biosphere Reserve | 🇲🇽 Mexico | |
| 4 | Channel Islands National Park | 🇺🇸 United States | |
| 5 | Celestún Biosphere Reserve | 🇲🇽 Mexico | |
| 6 | Arrecifes de Cozumel National Park | 🇲🇽 Mexico | |
| 7 | El Vizcaíno Biosphere Reserve | 🇲🇽 Mexico | |
| 8 | Merritt Island National Wildlife Refuge | 🇺🇸 United States | |
| 9 | Everglades National Park | 🇺🇸 United States | |
| 10 | Sian Ka'an Biosphere Reserve | 🇲🇽 Mexico | |
| 11 | Cabo Blanco Absolute Nature Reserve | 🇨🇷 Costa Rica | |
| 12 | Ciénaga de Zapata | 🇨🇺 Cuba | |
| 13 | Tayrona National Natural Park | 🇨🇴 Colombia | |
| 14 | Big Cypress National Preserve | 🇺🇸 United States | |
| 15 | Bastimentos Island National Marine Park | 🇵🇦 Panama | |
| 16 | La Amistad International Park (Panama) | 🇵🇦 Panama | |
| 17 | Carara National Park | 🇨🇷 Costa Rica |
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Miami | 🇺🇸 United States | |
| 2 | Baltimore | 🇺🇸 United States | |
| 3 | Los Angeles | 🇺🇸 United States | |
| 4 | San Diego | 🇺🇸 United States | |
| 5 | Mexico City | 🇲🇽 México | |
| 6 | Barranquilla | 🇨🇴 Colombia | |
| 7 | New York City | 🇺🇸 United States | |
| 8 | Boston | 🇺🇸 United States | |
| 9 | Dallas | 🇺🇸 United States | |
| 10 | San Francisco | 🇺🇸 United States |
| # | Zoo / Centre | Country | |
|---|---|---|---|
| 1 | Key West Butterfly and Nature Conservatory | 🇺🇸 United States |
Rare
Under 5% of wildlife watchers report a Least Tern sighting in San Francisco on a given day, based on 1,076 verified sightings from GBIF citizen-science data. It is the 194th most-seen of the 375 birds we can rate there. Over three days the chance rises to under 5%, and over a week to about 10%, if each day is a fresh chance.
July
In that month about 10% of wildlife watchers report a Least Tern in San Francisco on a given day, against under 5% in August to June, the lowest months. That is one of San Francisco's driest months, with almost no rain against 110 mm in December.
Between 7 and 10 am
Across all the parks we cover, that three-hour window holds the most Least Tern sightings with a recorded time, and about 9 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
Among the best
Of the 14 cities where we can rate Least Tern sightings, San Francisco ranks 10th at under 5%, level with the leaders once rounded. The best odds are in Miami (United States, under 5%), Baltimore (United States, under 5%) and Los Angeles (United States, under 5%).
Same family: Laridae
The closest relatives of the Least Tern that you can see in San Francisco (family Laridae, Gulls, Terns, and Skimmers) are California Gull (about 40%), Western Gull (about 30%) and Ring-billed Gull (about 20%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Least Tern is recorded against all the birds logged in San Francisco (1,076 verified sightings), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
