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Two hundred years ago, millions of birds including Long-Billed Dowitchers, Snow Geese, and Sandhill Cranes migrating south from Alaska to the southern tip of Mexico would have had no problem finding prime wetland real estate along their routes. Back then, the regular flooding of California’s Central Valley’s surging Sacramento and San Joaquin Rivers created some 4 million acres of wetland, .

The birds migrating today are not so lucky—agriculture and development in the Central Valley has filled in 95 percent of the original wetland habitat. Around of managed Central Valley wetlands remain for millions of migrating birds, and California’s four years of haven't helped.

"For a bird, it's about the landscape—what is out there as a whole—not one patch or another," says Meghan Hertel, working lands director at Լ����Ƶ California. If birds don’t find proper habitat with plenty of food and water, they won’t be able to refuel for migration. And if they find limited water, they’ll crowd together around it and risk spreading disease, which could cause a mass die-off.

Since the rise of agriculture in the Central Valley, little if any wetland habitat would exist without the dedication of conservationists and landowners. Because all flowing water has been diverted into a vast system of aqueducts and canals, each wetland must be created by turning on a spigot—an act somewhat reminiscent of a futuristic dystopian film. "Literally our wildlife refuge managers have to go out to turn on or off water to flood the refuges," Hertel says. A vast legal framework decides who gets how much water—and then it’s up to landowners to ration out their year’s water allotment (and pray for rain).

Thanks to the drought, each year the amount of water allotted to the refuges gets smaller and smaller. (Լ����Ƶ California and other non-profits advocate for larger annual water allotments via the .) But to make the most of the water they do have, land managers have learned to be more strategic by flooding wetlands only when and where the birds need them. Their data-driven, coordinated approach allows them to get the biggest bang out of their paltry water budget.

Here are three ways California refuges and land managers have learned to make the most out of their limited water:

1. Getting the Timing Right

Kern National Wildlife Refuge Complex, the southernmost refuge in the Central Valley, hosts 6,500 acres of wetlands in a good year. In the fall of 2014, however, refuge manager Nick Stanley created less than a quarter of that. Already short on water thanks to the drought, he flooded his wetland habitat in September to get ready for the birds’ arrival. But the air was too hot and the ground too dry—half of the water sunk into the ground or evaporated before the birds even arrived.

This year is at least as hot and dry as last year, and he doesn’t want to risk wasting water again. So he waited until early October to start flooding his wetlands. Even though we’re months into migration season, Stanley's only created 200 acres of wetland (out of an expected 1,500 acres) so far this year.

It’s a risk he's willing to take only because he knows the birds have habitat elsewhere—thanks to a large-scale effort to coordinate among Central Valley’s wildlife refuges.

Every two weeks, representatives from each Central Valley wildlife refuge get on the phone to share updates from their land—mainly whether birds have arrived and whether they need more space. These on-the-ground reports allow each manager to make more informed decisions about when their water will most benefit birds, and allow the entire area to provide more consistent habitat throughout migration.

Thanks to those calls, Stanley knew that the birds had plenty of wetland space available at the northern refuges, and that he’ll get a heads up if and when the birds approached Kern.

“In the past, we would probably glance over at what other refuges are doing, but with the effects of the drought it’s a little more detailed and a lot more coordinated,” Stanley says.

2. Distributing the Wealth Where It’s Needed the Most

The closer the refuges are, the higher the level of coordination. For instance, if a refuge worker notices bird overcrowding in one area of her own refuge, she can call the refuge next door and ask them to flood an area to give the birds more space.

They can even reallocate water reserves depending on where they’re most needed. For example, last winter, surprise December rains rolled through the northern wildlife refuges and flooded their wetlands, while 300 miles south Kern was left high and dry. When this disparity came to light, Sacramento and San Luis National Wildlife Refuges transferred excess water to Kern, which Stanley used to create an additional 2,000 acres of wetland habitat for the birds in the parched south.

This kind of collaboration helps relieve the drought-related water crunch. “We’re all feeling the impact,” Stanley says. “That’s why we're doing the coordination calls.”

3. Collaborating with Farmers to Create “Pop-Up” Wetlands

Wildlife refuges can’t make up for all the wetland that’s been lost. So to fill the gap, since 2014, even privately owned land (mostly rice fields) has been converted to suitable habitat for birds during migration, says Mark Reynolds, head scientist of the Nature Conservancy’s .

Each fall, rice farmers flood their fields with two to four inches of water to break down rice stubble—making the paddies ideal migratory bird habitat. But the flooding is timed to agricultural cycles, not bird migration. So the Nature Conservancy to flood the fields early, when the birds show up.

To figure out when that’s most likely to happen, Reynolds worked with quantitative ecologist Matt Reiter, of Point Blue Conservation Science, to and bird migration patterns. Data from Landsat satellite imagery showed where water is most scarce while data from eBird predicts when the birds will be where. The highlights areas with many birds but few wetlands—ideal places to look for cooperative rice farmers. Then, using guidelines developed by Point Blue and Լ����Ƶ California on how to flood rice paddies to most benefit birds, they started asking farmers to get on board.

Since the spring of 2014, the program has created nearly 25,000 acres of pop-up wetland on rice fields. And the birds have been using them: About 30 times more shorebirds forage at BirdReturns rice fields than at fields flooded to the agricultural cycle, according to the Nature Conservancy. “It’s especially heartening going out to the fields with the farmers and seeing abundant wildlife in an agricultural setting,” Reynolds says.

Reiter is now working with wildlife refuges (and others) to develop his model into an automated water tracking system that land managers across the Central Valley—wildlife refuge managers, private landowners, and conservation groups—could use to coordinate wetland creation at the landscape level. With drought conditions seemingly here to stay, this could have a big impact—though most bird species seem to be faring all right so far.

“If we go into another few years of this rotation of not having enough water and not being flooded up, I think there will be a bigger impact,” says Stanley, Kern’s refuge manager. “But most birds still have good breeding populations, so I think we’re still okay.”

That includes the dowitchers, which use the BirdReturns rice fields in the greatest numbers. Between the patchwork of refuge wetlands and rice fields, at least this year they may have enough food and habitat to fuel them for the next leg of their migration. But if the drought continues, even the best coordination may not be able to fill fields with water that isn’t there.