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On the Wing:
San Dieguito Lagoon
Ed Mirsky | Hoska Drive

American Avocet.
Photo © Steve Brad.
Click to enlarge.

My most memorable experience of spring migration was on Santa Barbara Island. Birds were flying in the fog overhead when my friend heard a soft chip call note, and called out “Wilson’s Warbler.” Soon, another birder heard a witch call and shouted “Connecticut Warbler.” And so the morning went as literally hundreds of warblers, some from wintering grounds as far away as Costa Rica, landed on the island and immediately began to forage. Connecticut Warbler? It seems to have taken a “wrong turn”; most of its kind use the Atlantic Flyway to reach breeding grounds in Canada.
The San Dieguito monthly bird count has been conducted on the first Sunday of the month since 2010. Some of the highest numbers counted during that period were 589 Western Sandpipers in February 2010, 328 Least Sandpipers in January 2011, and 660 American Wigeon in 2017 to name a few. We know that not all the individuals of a species are seen, but the data gives the long-term trends.
There are many migration patterns:

• nest at the lagoon and nowhere else. Belding’s Savannah Sparrow and Ridgeway’s Rail are examples.

• breed elsewhere and stop at the lagoon and other coastal mudflats, rocky shorelines, and inland habitats during migration and in winter. Examples are Least Sandpiper and Green-winged Teal.

• nest at the lagoon and are joined by migrants passing through in spring and fall. This is common among shorebirds such as the American Avocet, ducks such as Gadwall, and Yellow Warbler and Peregrine Falcon.

• migrate to the lagoon to breed. The Least Tern winters across marine coastlines of Central and South America, and returns to nest on relatively open beaches and islands kept free of vegetation. None has nested in any of the five white-sand nest sites built throughout the lagoon during the restorations, but there are productive colonies that have endured for years in the county.

• non-breeding birds remain at the lagoon while adults go to the summer breeding grounds. This is the reason Spotted Sandpipers are seen along the shores of sloughs and channels during the breeding season.

• pass through the lagoon on their annual migration to their breeding grounds. In the spring the Rufous Hummingbird travel nearly 4,000 miles from wintering sites in Mexico to breeding grounds in Alaska and northwest Canada, and make the return trip in the fall. By the way, our backyard bird often confused with Rufous is the Allen’s Hummingbird.

These migratory patterns beg the question, How can so many similar bird species use the lagoon during migration? A hint is offered by the American Avocet. It sweeps its upturned bill from side-to-side over the water surface to collect aquatic invertebrates that are mostly unavailable to other species. But how do the other shorebirds find enough food at the lagoon? To answer that question, go to the lagoon and observe and wonder.


 

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