As many as 500,000 migratory shorebirds on the Pacific Flyway stopover for critical refueling in the Central Valley during spring and fall migration, including species such as Western and Least Sandpiper and Dunlin. In spring, they arrive from wintering grounds as far south as the Chilean coast of South America, stocking up on benthic invertebrates in shallow-flooded ricelands, managed wetlands, and mudflats. Once they have refueled, many shorebirds continue their journey to breeding grounds as far north as the Arctic tundra. In fall, they complete the reverse journey.