Sterna trudeaui
Silhouette: Sharon Wegner-Larsen · PhyloPic
In 3 days ~10% in a week ~20%
The snowy-crowned tern (Sterna trudeaui), also known as Trudeau's tern, is a species of bird in subfamily Sterninae of the family Laridae, the gulls, terns, and skimmers. It is native to Argentina, Brazil, Chile, Uruguay, and possibly Paraguay, and also vagrant in Peru and the Falkland Islands.
Some genetic data indicate that the snowy-crowned tern and several other closely related terns belong in a genus separate from Sterna. At the least, the snowy-crowned and Forster's tern (S. forsteri) are sister species. The snowy-crowned tern is monotypic.
The snowy-crowned tern was first described by the American ornithologist John James Audubon in 1838. He had been sent a specimen by his friend Dr. James de Berty Trudeau (1817–1887) of Louisiana, who had reportedly found several of the terns at Great Egg Harbor Bay, New Jersey. Audubon named the bird in his honor.
The snowy-crowned tern is 28 to 35 cm (11 to 14 in) long with a wingspan of 76 to 78 cm (30 to 31 in) and weighs 146 to 160 g (5.1 to 5.6 oz). It has a rather blocky head, a thick neck, long wings, and a forked tail. The sexes have the same plumage. Adults in breeding plumage have a... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|
More parks will be added in future updates.
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Montevideo | 🇺🇾 Uruguay | |
| 2 | Buenos Aires | 🇦🇷 Argentina | |
| 3 | Santos | 🇧🇷 Brazil |
Rare
Under 5% of wildlife watchers report a Snowy-crowned Tern sighting in Buenos Aires on a given day, based on 358 verified sightings from GBIF citizen-science data. It is the 158th most-seen of the 274 birds we can rate there. Over three days the chance rises to about 10%, and over a week to about 20%, if each day is a fresh chance.
September
In that month about 10% of wildlife watchers report a Snowy-crowned Tern in Buenos Aires on a given day, against under 5% in October to August, the lowest months.
Between 3 and 6 pm
Across all the parks we cover, that three-hour window holds the most Snowy-crowned 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.
2nd of 3
Of the 3 cities where we can rate Snowy-crowned Tern sightings, Buenos Aires ranks 2nd at under 5%. The best odds are in Montevideo (Uruguay, about 20%).
Same family: Laridae
The closest relatives of the Snowy-crowned Tern that you can see in Buenos Aires (family Laridae, Gulls, Terns, and Skimmers) are Brown-hooded Gull (about 10%) and Dominican Gull (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Snowy-crowned Tern is recorded against all the birds logged in Buenos Aires (358 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.
