The BirdReturns program, financed by the Nature Conservancy, then pays rice farmers in the birds’ flight path to keep their fields flooded with irrigation water from the Sacramento River as migrating flocks arrive. The prices are determined by reverse auction, in which farmers bid for leases and the lowest bidder wins.

Because the program pays for only several weeks of water instead of buying the habitat, the sums are modest; the conservancy does not disclose bids because that might affect future auctions, but it says the figures were both above and below the $45 per acre that the federal government pays for bird-friendly practices.

The project’s first season ended last month, as birds headed north from newly flooded fields. Researchers said all of the birds whose numbers they hoped to improve were seen on “pop up” wetlands — a temporary steppingstone for the birds’ journey north. This happened when the field would have ordinarily been drained, an indication that the approach was working. More analysis will be done this month. The fields will be flooded again in the fall for the birds’ return journey. Eventually, using this and other approaches, the conservationists at BirdReturns hope to increase the number of shorebirds that stop in the Central Valley to 400,000, from current levels of 170,000.

BirdReturns is an example of the growing movement called reconciliation ecology, in which ecosystems dominated by humans are managed to increase biodiversity.