Can you name this bird?

You are facing northwest on a trail that runs east-west. Parallel to the trail is a standing body of water that is probably fresh or perhaps brackish. It is mid-day, in June. In the sedges or cattails below and to the left a bird keeps calling, but does not come out. Even walking up close to the spot where the bird calls does not flush it, although it does go silent until you leave.

<-- Ocean to the left, 1/4 mile


Pescadero Marsh
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What am I?