California Gulls: If not Mono Lake, where?

The California Gull (Larus californicus), the iconic gull species at Mono Lake and the state bird of Utah, is in trouble. These soaring and gregarious birds have nested in large numbers for millennia at Mono and Great Salt Lake, returning each year to the same patch of ground and reuniting with their mates. The gulls are an indicator of the health of these simple yet extremely productive saline lake ecosystems. Feeding on brine shrimp and alkali flies, gulls gather to nest and raise their young on predator-free islands, mixing with millions of other migratory and breeding birds along a flyway network that links states, provinces, countries, and continents.

Tragically, Great Salt Lake recently fell to its lowest level in history due to water diversions and drought. Mono Lake, while provided protection on paper three decades ago, has yet to reach its healthy Public Trust lake level due to continuing water diversions by the Los Angeles Department of Water & Power (DWP). Another large California Gull breeding site in the South San Francisco Bay, a relatively new colony established after landbridging caused gulls to abandon nesting grounds at Mono Lake, has an uncertain and complicated future—gulls at this location are unwelcome newcomers and their habitat will shrink as tidal marsh restoration progresses.

Together, these locations support half of the world’s population of the species, and all three are experiencing concurrent threats or potential catastrophic disruptions. Mono Lake is unique among them—its necessary healthy level was determined and ordered, and it’s the most easily restored and protected by simply pausing water diversions until the lake reaches a more stable, drought-resistant lake level for gulls.

DWP transfers ecosystem problems beyond Mono Lake

Negit Island, the distinctive black cinder cone island in Mono Lake, was once home to the largest California Gull breeding colony in California. DWP ended that in 1979.

Excessive water diversions of Mono Lake’s tributary streams beginning in 1941 lowered the lake more than 40 feet and exposed thousands of acres of salt- and alkali-encrusted playa. The shallow region between Negit Island and the lakeshore was exposed, forming a landbridge that allowed hungry coyotes easy access to eggs and chicks. The coyotes decimated the gull colony and tens of thousands of gulls did not nest that year.

By 1980 the largest California Gull colony in California was in chaos. Many birds shifted to Negit’s neighboring rocky islets, but gulls remember nesting disruptions. Some, recalling the trauma of predation, may have given up on Mono Lake completely and searched for new habitat. In 1980, California Gulls began to expand their breeding range to the south and west and that year 24 individuals were detected nesting in an estuary in the South San Francisco Bay. By 2014 their numbers there had exploded to 53,000.

This new gull colony found abundant nesting habitat and easily available food at landfills. Today, an estimated 45,000 breeding adults are in the South Bay and the gulls have had significant impacts on other species, preying on other nesting birds. Monitoring of nesting populations showed that in this region California Gulls regularly eat the eggs and chicks of American Avocets, Black-necked Stilts, Forster’s Terns, and Western Snowy Plovers.

The South Bay Salt Pond Restoration Project, the largest tidal wetland restoration effort on the West Coast, is, in part, dealing with the effects of the influx of displaced California Gulls. The gulls are hazed, their breeding habitat is flooded, and nesting levees have been breached to restore wetland habitat. Gulls are not being harmed as restoration advances, but land managers must actively discourage them from nesting near shorebirds and terns, whose productivity and survival the gulls negatively impact.

Over time as salt marsh restoration succeeds and sea levels rise, California Gulls will lose nesting opportunities in the South Bay. This region is not a long-term refuge for the species. The South Bay colony paints an unwelcome picture of an ecosystem chain reaction, where displacement of birds from one region, due to water diversions, transfers problems to another.

A catastrophic forecast for Great Salt Lake

Across the Great Basin from Mono Lake, Great Salt Lake is home to the largest concentration of nesting California Gulls in the world. An estimated 120,000–160,000 birds nest around the lake’s expanse. Great Salt Lake has dropped to historic low levels, having lost 73% of its water and 60% of its surface area due to unsustainable water diversions. Recent drought has accelerated the lake’s decline, and according to John Neill, an avian biologist with the Utah Division of Wildlife Resources, nearly all the California Gull nesting sites around the lake today are “landbridged,” meaning accessible to ground predators like coyotes and foxes. Neill says, “While no one has observed large-scale abandonment, these birds are not well monitored.”

An alarming new technical report indicates that within the next five years Great Salt Lake will experience steep decline, experience irreversible food web collapse, and become a public health threat unless consumptive water use within the watershed is immediately cut by 33–50%. The study, released in January 2023, was cooperatively published by 32 researchers led by Brigham Young University. While this wet winter’s precipitation has recently raised the level of the lake, it is only a temporary reversal of fortune.

What will happen to the gulls at Great Salt Lake? No one can accurately predict but if the lake is not protected, the impacts will be catastrophic not just for gulls, but also for millions of other birds, and for the 1.2 million human residents of the greater Salt Lake City area.

Hanging on at Mono Lake

Mono Lake has not yet recovered from decades of excessive water diversions and it is only 30% of the way to its mandated Public Trust lake level, set by the California State Water Resources Control Board in 1994. Seventy percent of the nesting California Gulls at Mono Lake use one small islet near the landbridge—the same landbridge that DWP diversions created decades ago.

DWP insists there is no landbridge and that there is no crisis for California Gulls, ignoring evidence that coyotes accessed nesting islands by wading and swimming in years when the landbridge was not fully connected. The landbridge brings coyotes physically closer, within tantalizing sight, scent, and sound of nesting gulls. Coyotes were documented on Negit Island and nearby Java Islet as recently as 2016, forcing the abandonment of more than 400 nests.

This winter the Committee had planned to install a temporary solar-charged electric fence to help protect the gulls from coyotes. The fence worked six years ago and disaster was averted in 2017. This exceptionally wet winter caused the lake to rise to 6380 feet above sea level by the time gulls began nesting, the minimum level needed to reduce the chance of coyotes accessing the nesting islands. The unexpectedly and miraculously wet winter provided the remedy that DWP was unwilling to provide—more water for the lake. Instead of the fence, the Committee will install a monitoring system using a network of wildlife cameras and Point Blue Conservation Science will implement additional field monitoring for coyote activity during this year’s gull research.

Mono Lake will continue to rise through this summer. However, until either DWP or the State Water Board takes action to change diversion criteria to ensure a buffer for Mono Lake, the cycle will likely continue—a warming climate will likely bring more severe drought years, the lake will drop too low, and coyotes will once again threaten nesting gulls.

There are no other nesting opportunities at Mono Lake safe from coyotes. Great Salt Lake is on the verge of collapse and the South Bay is not sustainable. If not Mono Lake, then where? As Ryan Burnett, biologist with Point Blue, stated at the Mono Lake State Water Board workshop, “Mono Lake likely represents the single best place for California Gulls to nest. Ensuring predator-free nesting habitat and a productive lake ecosystem is critical to their long-term viability.”

This post was also published as an article in the Winter & Spring 2023 Mono Lake Newsletter. Top photo by Bartshe Miller.