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A story about Caspian Terns within another story about Caspian Terns

May 5th, 2013 · by Garrison Frost

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The Caspian Tern is the tern’s tern. Sure, in California we talk about the California Least Tern, a compelling story for sure – but if one tern stands above the others, it is probably the Caspian. The Caspian is bigger, more aggressive, and has that fire red bill that you can see from a mile away. But it’s only part of this story that the Caspian Tern is filling up the Pacific Flyway right now, heading to breeding sites from California up through Canada. There’s an aspect to this story that’s far less hemispheric, a testament to how one well-considered restoration project in a small bay can tap into a flyway full of birds (Caspian Tern photos by Kerry Wilcox).

Last week, Rachel Spadafore was unpacking her gear on Aramburu Island in Richardson Bay, when a large tern flew down on her in an attacking move. The Audubon restoration ecologist had seen this kind of thing before, and she thought nothing of it until the bird came back again and again, each time just missing her head. Another bird joined in. As she put her hands over her head for protection, she looked down the beach, where she saw a row of terns, their crests ruffling in the breeze.

Spadafore was seeing a very specific behavior where terns defend territory that they’re using for roosting and mating. Through her binoculars, she was able to recognize both Caspian Terns and Forster’s Terns. Before the restoration of this island, there had never been such activity here. Not remotely.

That’s because prior to 2009 when Audubon first began restoring this little island opposite our Richardson Bay Audubon Center & Sanctuary, this island was nothing but dredge spoils and invasive plants. No beach existed, just a steadily eroding edge, practically useless to these birds. Here’s what the shoreline looked like in 2009 before we started:

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The new shoreline where Spadafore saw the terns is a carefully engineered design made with sand and bright white oyster shell, specifically meant to provide roosting and nesting opportunities for tern species:

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Imagine her joy at seeing these birds here, on habitat that we made specifically for them. When you do a project like this, there’s never a guarantee that the birds will respond – but apparently they have in a big way.

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“This is what restoration looks like,” says Spadafora.

While it is something of a surprise that the Caspian Terns have taken to Aramburu, their presence in San Francisco Bay is right on time. The Caspian Tern has been spotted on every continent with the exception of Antarctica. In the Pacific Flyway, it winters far south in Mexico, Central America, even Columbia. In the spring, it heads north to specific breeding sites all into Alaska.

The birds were already starting to arrive in March, as you can see on the eBird map below:

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But by April, they were really starting to fill out the flyway:

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Categories: Audubon California · Birding · Pacific Flyway · Richardson Bay Audubon Center & Sanctuary · S.F. Bay · spring migration

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