Though not nearly so rich as it was when the first visiting Spaniards described the sky as darkened with birds, the bay remains one of the best birding locations in North America. More than 250 species spend at least part of the year here, and at any given time there are as many as 800,000 individual water birds paddling, skimming, flapping, preening, or diving. Quite often, especially in winter, there is no greater concentration of this population of ducks, grebes, plovers, godwits, willets, sandpipers, egrets, terns, and herons than in Arrowhead Marsh on San Leandro Bay, at the southeast end of the island of Alameda. Bicycling the trails of the Martin Luther King Jr. Regional Shoreline with your binoculars is a great way to cover the distance. Or to get a closer look, borrow a boat and go paddling.