Bird-lovers flock to Pescadero Marsh Natural Preserve (www.parks.ca.gov [1]), located on Highway 1 right across the freeway from Pescadero State Beach [2]. This protected wetland is home to a variety of avian species, including blue herons, great and snowy egrets, and northern harriers.
For the best birding, visit the marsh in late fall or early springtime, when migration is in full swing.
Links:
[1] http://www.parks.ca.gov
[2] http://www.moon.com/destinations/california/san-francisco-and-the-bay-area/coastside/pescadero/beaches