The trickle of water, the trill of a bird, the whoops and bellows of feeding humpback whales. Songs about nature and the sounds of the natural world will combine to create a unique Earth Day concert on April 21 at St. Stephen’s Episcopal Church in Belvedere. Billed as “Ecomusicology: Exploring our Environment through Sound,” the concert is a collaboration between the musicians of St. Stephen’s and the scientists at the San Francisco State University’s Estuary and Ocean Science Center, said St. S