Sunday, October 1, 2017

Elegant Terns at Moss Landing Harbor

The harbor in Moss Landing is a great place to see thousands of Elegant Terns (Thalasseus elegans) in the later summer and early fall.  They gather on the jetty and dry spits of land in large numbers, making quite the to-do and drawing a good amount of attention while they are here.  (Watch a flock of terns sometime and you'll understand what I mean!)  But very soon they will leave our shores to migrate south for the winter.

Only five breeding colonies of Elegant Terns are known today, down from twelve colonies historically.  Between 90 and 97% of all Elegant Terns breed on Isla Rasa in the Gulf of California.  One other breeding colony is found off the coast of Mexico, and since the mid-1900's three breeding colonies have become established on the coast of southern California.  This is the most restricted breeding range of any North American tern, making Elegant Terns vulnerable to human disturbance and habitat loss.  Due to their limited breeding range, Elegant Terns are listed as vulnerable or near threatened.  

In Mexico, breeding colonies of Elegant Terns are often associated with colonies of Heermann's Gulls and Caspian Terns, the smaller terns probably seeking the protection offered by the larger species.  Terns are highly social birds, nesting on the ground in colonies with thousands of birds packed closely together.  Nests are little more than scrapes on the ground, and a clutch consists of just one or two eggs.  A few days after hatching, chicks are old enough to leave the nest and join the other chicks of the colony, which gather together in a large group called a "crèche."  During this time, adult terns feed only their own chick(s), able to single out their young from the crowd by sound.

During the late summer and early fall, after the breeding season is finished, Elegant Terns leave their breeding grounds and move north along the coast of California to feed.  Occasionally, but rarely, they reach as far north as southern Washington.  Elegant Terns return south in October, spending the winter along the coast of central and south America, as far south as Peru and Chile.

Elegant Terns are a strictly coastal species, almost never found inland.  They commonly concentrate in large numbers around estuaries and bays (like Moss Landing).  Like other terns, Elegant Terns feed on fish which they spot from above while flying, and catch by making spectacular plunging dives into the water.  Watching a flock of terns is a great form of entertainment!

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