Water savings may cause suffering for burrowing owls
Can the tiny raptors adapt to irrigation changes in California’s warming farm fields?
On a scorching September morning, three curious young owls peer out from a burrow carved out of a sunbaked irrigation ditch. They train their bright yellow eyes on me, barely moving a feather. “There’s one hunkered down, pretending to be a rock,” says Stevie Sharp, pointing to a slightly larger owl, perhaps the trio’s parent, standing sentry above the burrow. “Sometimes you see them, sometimes you don’t.”
Today, Sharp and I see plenty of owls, a bird nearly every 20 feet or so, along the hay fields or perched atop stakes scattered along one of the hundreds of canals that deliver Colorado River water to half a million acres of farmland in Southern California’s Imperial Valley. Sharp, an environmental specialist with the Imperial Irrigation District, pounds a stake with a bright pink ribbon stamped “owl burrow” into the parched ground next to the ditch. She flags burrows anytime a district project could disturb nesting owls, to help maintenance and construction workers avoid them.
For decades, the Imperial Valley, where the hardpan Sonoran desert meets the verdant agricultural fields that stretch from Mexico to the Salton Sea, has provided an improbable refuge for these owls. They were once relatively scarce here, but now the valley harbors 70 percent of the state’s population, thanks to a 3,100-mile irrigation system that transformed this stretch of desert into a multibillion-dollar agricultural industry. The sprawling patchwork of irrigated farmland offered owls the ecological equivalent of big-city living: Round-tailed ground squirrels easily tunnel through the earthen canals, providing abundant nesting sites, and agricultural fields support a well-stocked buffet of insects and rodents.
Burrowing owls flourished here as a happy accident of industrial agriculture, when they were mostly left to their own devices. But that began to change when the Imperial Irrigation District was forced to find ways to conserve water in a farm-to-city transfer agreement negotiated in 2003. Now, after years of water-tightening measures — and increasing loss of farmland to renewable energy production — biologists worry that owls may not be able to adapt to this rapidly changing landscape.
“Numerous efforts to conserve water, which is a good thing, have taken a toll on the burrowing owls,” says Courtney Conway, director of the U.S. Geological Survey’s Idaho Cooperative Fish and Wildlife Research Unit and professor at the University of Idaho.
“It’s a conundrum,” says Conway, a leading authority on burrowing owls. The population grew as owls took advantage of an artificial system and a laissez-faire approach to water delivery, he says. “Now they’re declining in the Imperial Valley because we as a society are trying to get better at water conservation there.”
Imperial Valley agriculture has depended on imported water since entrepreneurs dug the first canal to divert water from the Colorado in 1900. The All-American Canal now provides that lifeline, turning a region with about 3 inches of rain a year into one of the nation’s most productive farming areas. The Imperial Valley, aided by year-round irrigation, produces 100 different crops, from alfalfa hay to wheat, and supplies about two-thirds of the nation’s winter vegetables.
Western burrowing owls love to congregate along the lateral canals fed by one of the three main arteries that carry Colorado water to the irrigation district. They mostly tolerate the low roar of hay balers and passing trucks but invariably scatter as I approach, diving through the air like dolphins before alighting about 40 feet away. From a safe distance, they start hissing and bobbing, hoping I’ll go away. Nesting season has ended, but remnants of scat, clothing and other scavenged tidbits still adorn their burrow entrances, likely signaling other owls to find another nest.
This robin-sized raptor, barely heavier than a baseball, once bred throughout North America’s grasslands and deserts. But populations have tumbled nearly 40 percent over the past several decades, victims of our penchant for developing open spaces, spraying pesticides and persecuting the burrowing animals that build their subterranean hideaways.
California listed Western burrowing owls as a “species of special concern” in 1978. Conservation groups petitioned the state to list the birds as threatened or endangered in 2003 — the same year water managers ramped up conservation measures — but officials refused, pointing to the healthy Imperial Valley population. Now, that population appears to be declining as well. Conway thinks lining 23 miles of the All-American Canal with concrete to prevent water from seeping into the dirt banks may have contributed to the decline by inadvertently destroying suitable nesting sites.
Breeding pairs in district lands have dropped from about 6,500 in the early 1990s to 4,000 in 2012, according to Audubon California’s latest estimates. Irrigation district surveys over the past year identified about 3,330 burrows, but did not estimate owl numbers.
Figuring out how many owls live in the irrigation district is far less important than improving methods to avoid them, says Dan Rosenberg, an ecologist at the Oregon Wildlife Institute and Oregon State University who has advised the Imperial Irrigation District. Rosenberg reported in 2006 that maintenance of canals and roads inadvertently buried three owls in their burrows near the Salton Sea. Yet maintenance can also benefit owls by clearing vegetation from canals, giving them a clear line of sight to hunt and avoid predators. Thanks to water district training programs, no owls have been killed over the past decade, aside from one incident, when a worker knocked a piece of concrete loose and crushed an owl, according to reports filed with the state. Yet even the best avoidance methods can’t be 100 percent accurate, Rosenberg says. “There are just too many owls and too much landscape.”
The tiny raptors must also contend with vehicle collisions, pets and illegal shootings, along with loss of habitat to development and a burgeoning renewable energy industry. Agriculture is still the main economic driver in the valley. But farmland is increasingly being converted to solar, wind and geothermal projects to meet California’s Renewables Portfolio Standard, which requires utilities to get a third of their electricity from renewable sources by 2020.
Ironically enough, the owls are in trouble because we’re getting better at conserving resources: Loss of farmland to green energy plants, like lining dirt canals with concrete, means loss of habitat for burrowing owls.
Owls are often relocated to accommodate solar farms and other renewable energy projects in programs the state calls “mitigation,” Rosenberg says. “You might call it humane removal, in the sense that you’re moving it out of harm’s way,” he says. “But you’re not protecting that owl population. If you’re going to develop an area and you’re not increasing their habitat somewhere else, it will cause a decline. It’s not mitigation.”
The loamy soil that supports the cornucopia of crops here retains the grayish, red-brown palette of the surrounding desert. That palette suits the burrowing owls’ spotted coats, which make them nearly impossible to spot against the sun-dappled earth — until a vulture flies overhead and the “earth” looks up. In the fields beyond the burrows, white-faced ibises, gulls and cattle egrets join owls to feast on the insects that feed on the crops.
They had far more food when alfalfa farmers routinely flooded their fields. “Crickets and other bugs start popping up from the ground, and the birds quickly tune into that and feed along the advancing line of water,” says Christian Schoneman, a U.S. Fish and Wildlife biologist and manager of the Sonny Bono Salton Sea National Wildlife Refuge. “You’ll get thousands of birds feeding in a single field taking advantage of this.”
As growers have turned to sprinkler irrigation, which uses about half of the water that flood irrigation uses, Schoneman says, owls and other birds have lost that food source.
Less water in the fields also means less water diverted to California’s largest and most endangered lake, the Salton Sea, which supports millions of overwintering birds.
Biologists think burrowing owls from other regions may overwinter here, too. And though most Imperial Valley owls stay here year-round, Conway says, it’s possible that some disperse to a handful of dwindling populations along the coast. “We can’t say for sure that Imperial Valley owls are providing that source,” he says, “but it’s likely that they’re at least contributing.”
The state promised to come up with a comprehensive conservation plan to protect California’s declining populations in 2008, but never did. “We ran out of money,” says Esther Burkett, statewide coordinator for burrowing owls for the California Department of Fish and Wildlife. State officials drafted conservation guidelines in 2012, but they have no regulatory teeth. The state still needs to get a better handle on population trends and how owls are affected by being relocated, Burkett says.
Lack of information is not the problem, Rosenberg believes. “Nobody wants to make these decisions because of the impact on development,” he says. “Instead, they’ve been moving (owls) around — calling it mitigation, as if that solves the problem.”
The good news, says Conway, is that burrowing owls are highly adaptable. “There are so many other species, like sage grouse, where it just takes a little development and they’re gone,” he says. “Burrowing owls are definitely not that way.”
Yet, as the decline of the owls throughout their range attests, even this highly adaptable species has its limits. For decades, these plucky little raptors thrived on the incidental benefits of an artificial landscape managed for farming, not wildlife. But if the conditions that allowed burrowing owls to bloom in this desert disappear, they’ll need more than benign neglect to survive.
Liza Gross is an independent journalist based in the San Francisco Bay Area who writes frequently about the intersection of science and society. She is also the author of The Science Writers’ Investigative Reporting Handbook. Follow @lizabio
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