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Courting Decoys
Brian Foster, PhD, Contract Biologist

 

 
Courting the Real McCoy. Photo from the US Fish and
Wildlife Service and belongs to the public domain.

 

It’s May and that means it is nesting season for the endangered California Least Tern. As these birds return from their migration they will have four newly reconditioned sites waiting for them just across the river from the Del Mar Fairgrounds and overseen by the 22nd Agricultural District. These sites were prepared as mitigation by Southern California Edison as part of the larger planned rehabilitation of the San Dieguito River estuary. Each of the sites has a newly placed sand and oyster shell cap that, it is hoped, appears ideal to terns looking to establish nests. The sites appear as white areas visible on either side of the freeway from Interstate 5, south of the Via De La Valle exit.

The population of the Least Tern is considered endangered and had fallen to just 600 pairs in 1970. After decades of careful management, the population had rebounded to about 7,000-7,700 pairs in 2008. Since then there has been a decrease in the population of 15-20%, which makes the creation of new sites and colonies especially important.

The San Dieguito River Valley has not had Least Tern nesting in decades. The terns spend the winters down in Central and South America (as far as anyone knows since their winter range has not been scientifically established) and returned here to forage for fish in the recently created waterways. In order to let the terns know the nesting sites are meant for them, contract biologists have placed decoys on the sites to attract the terns. Decoys are effective at attracting terns as amorous male terns have even been observed offering the decoys a freshly caught fish as a mating inducement; the decoys never seem to respond, however. Ceramic Spanish tiles have also been provided to supply the chicks with shelter from sun and predators.

So far this season no nests have been established, but up to nine of the birds have recently been visiting the estuary, foraging for fish, courting, and even landing on one of the sites. Everyone is hopeful they will decide to stay and establish a new and productive nesting colony.


 

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