Earlier this year, Los Angeles made 8 trips to Encino Reservoir searching for one endangered bird; they found none, but 60 wildlife species emerged before a 10-acre solar project moved ahead

A quiet reservoir in Los Angeles became the setting for an unusually careful wildlife search in 2025. Biologists were looking for one small endangered songbird, the Least Bell’s Vireo, before a floating solar project could move ahead. They searched the same riparian habitat eight times across the breeding season and found no vireos. What they did find was a much broader picture of life around a reservoir that has been closed to the public for more than two decades, with 60 wildlife species recorded during the surveys.

The work was not a casual bird count. It followed a U.S. Fish and Wildlife Service protocol designed specifically to determine whether Least Bell’s Vireos are present in suitable habitat. The distinction matters because proving that an endangered species is absent is harder than simply failing to see one. A single missed bird can change the conclusion, which is why the federal guidance calls for repeated surveys during the breeding season. At Encino Reservoir, those surveys ultimately became one of the most informative pieces of the environmental review.

Why the Least Bell’s Vireo mattered at Encino Reservoir

The Least Bell’s Vireo, Vireo bellii pusillus, is a small migratory songbird associated with dense riparian vegetation, particularly the shrubs and trees that grow along rivers, streams and other wet areas. The birds are only about 4.5 to 5 inches long, with muted gray and pale plumage that can make them surprisingly easy to overlook among leaves. They arrive in Southern California breeding areas in spring, and their breeding season is precisely when biologists have the best chance of detecting territorial adults and nesting pairs.


Encino Reservoir contains the kind of vegetation that made the question worth asking. Along parts of the reservoir are Goodding’s willow and red willow riparian woodland, including habitat near the southwestern edge where several components of the proposed solar project would be located. Environmental documents classified the vireo's potential to occur there as moderate. Regional records also showed that the species occurs in the wider area, even though there were no known vireo territories on the reservoir property itself.

The search therefore focused on whether birds were actually using the habitat rather than whether the vegetation merely looked suitable on a map. That is an important distinction in wildlife assessment. Habitat can appear appropriate but remain unoccupied because of factors such as territory competition, food availability, vegetation structure, predators or the isolation of a habitat patch. In this case, nearby records meant the species could not simply be dismissed as irrelevant to the project.

Eight surveys were required for a reason

The federal survey guidance recommends at least eight surveys of potential Least Bell’s Vireo habitat between April 10 and July 31 under normal circumstances. Visits should generally be separated by at least 10 days, helping observers catch birds that arrive at different times and reducing the chance that a temporary absence will be mistaken for true absence. The protocol also accounts for birds that may be quiet, females that are less conspicuous and nesting pairs whose behavior can vary during the season.

LADWP's 2025 surveys closely followed that framework. Biologists visited on April 21, May 1, May 16, May 29, June 9, June 20, July 2 and July 14. The survey period therefore stretched from the arrival and early breeding period into midsummer, covering multiple points when a territorial vireo could reasonably have been detected. The survey area included suitable riparian habitat and a 500-foot buffer around relevant project areas.

Observers concentrated on locations where construction and project infrastructure could overlap with wildlife habitat. Those included the paved boat ramp, portions of the access road in the southwestern part of the reservoir and areas surrounding the proposed ground-mounted solar equipment. This approach was more precise than simply walking around the entire property looking for birds. It targeted the places where environmental effects from the project were most relevant.

And after eight separate searches, the result was consistent: no Least Bell’s Vireo was detected within the survey area. The environmental assessment therefore concluded that the species was absent from the project site and directly adjacent areas at the time of the surveys. That does not mean the species could never appear there. It means the protocol-level field evidence did not show an occupied vireo territory during the survey season.

The empty search produced a surprisingly full wildlife record

The more unexpected result came from everything else the biologists encountered. Across the eight Least Bell’s Vireo surveys, they recorded 60 wildlife species. The total included one amphibian, three reptiles, 54 bird species and four mammals. The survey was designed around a single endangered songbird, but the repeated visits effectively produced a broader snapshot of the reservoir's wildlife community.

That matters because urban reservoirs can be ecologically deceptive. From outside a fence, a closed water-storage facility may look like infrastructure surrounded by developed neighborhoods. Inside, however, long periods without public access can leave patches of vegetation relatively undisturbed. Encino Reservoir's 960-acre property is closed to the public, and the reservoir itself covers about 130 acres, creating a substantial block of restricted open space between surrounding residential development and the Santa Monica Mountains.

Earlier biological work had already shown that the site was being used by wildlife of conservation interest. A June 2023 survey recorded yellow warbler and coastal whiptail in the riparian area next to the reservoir. Neither is federally or state listed as endangered, but their presence demonstrated that the willow habitat was functioning as more than ornamental vegetation around an old water facility.

The environmental review also identified other species with potential to occur at the site. Crotch's bumble bee and western red bat were assessed as having high potential based on habitat and regional records, while the Least Bell's Vireo and two-striped gartersnake were assessed as having moderate potential. These categories are not claims that every species was present. They indicate how habitat conditions and known records were used to judge which animals could reasonably occur in the project area.

Why floating solar is being tested here

The wildlife surveys were part of a much larger experiment. LADWP is proposing a 5-megawatt floating solar array covering roughly 10 acres of the reservoir, along with a small 30-kilowatt ground-mounted solar system. The ground installation would provide a direct comparison with the floating technology, while a 5-megawatt, 20-megawatt-hour iron-flow battery system would be installed north of the reservoir.

The project is intended as a pilot rather than simply another solar installation. Floating photovoltaic panels allow electricity generation on a water surface instead of consuming additional land for a large ground array. At a constrained urban utility such as Los Angeles, that distinction can be significant. The Encino project is designed in part to determine whether this approach can work within LADWP's existing system and whether other in-basin opportunities might eventually support similar installations.

LADWP estimates that the project could produce about 10,280 megawatt-hours of electricity each year, enough to serve approximately 2,677 homes annually. The system would connect to an existing 34.5-kilovolt overhead distribution line crossing the property, allowing the pilot to use infrastructure that is already present rather than requiring an entirely new transmission corridor.

A reservoir built for water is becoming an unexpected ecological laboratory

Encino Reservoir has already gone through several lives. It was constructed between 1921 and 1924 to provide about 3,348 acre-feet of storage for Los Angeles. Population growth later drove a major expansion, completed in 1963, increasing capacity to about 11,606 acre-feet. After decades of service, the reservoir was decommissioned in December 2002 as water-quality requirements and the city's water system changed.

That history helps explain why the site is unusual today. It is neither a conventional public park nor untouched wilderness. It is a large piece of utility property containing a reservoir, roads, electrical infrastructure and treatment facilities, yet it also supports riparian vegetation and a surprisingly varied wildlife community. The absence of public access may have limited some disturbances that are common in more accessible urban natural areas.

The Least Bell's Vireo search brought that contradiction into sharper focus. The bird that triggered eight carefully timed surveys was not found, but the effort showed that the habitat was occupied by dozens of other species. In environmental science, that is an important reminder that absence of one sensitive species does not equal absence of ecological value. A landscape can fail to support one particular animal while still functioning as habitat for a much wider community.

The solar project has now cleared environmental review

LADWP prepared a California Environmental Quality Act Initial Study and Mitigated Negative Declaration for the project. The environmental document concluded that identified impacts would either be less than significant or could be reduced to less-than-significant levels through mitigation measures. The project received its Notice of Determination on July 14, 2026, with mitigation measures and a mitigation monitoring plan adopted as conditions of approval.

That approval does not erase the biological questions raised by construction. Instead, it reflects a regulatory conclusion that the project can proceed with safeguards designed to reduce environmental effects. The wildlife surveys were one part of that process, alongside reviews of water quality, vegetation, noise, wildfire risk, cultural resources and other potential impacts.

For the Least Bell’s Vireo, the conclusion is unusually specific. Eight searches conducted during the species' prescribed survey window found no birds at Encino Reservoir. Yet those same visits documented 60 other wildlife species, revealing an urban reservoir that is considerably more biologically active than its history as a closed water facility might suggest. As floating panels prepare to occupy part of its surface, Encino Reservoir is becoming a test not only of a new energy technology, but also of how modern cities can use old infrastructure without overlooking the wildlife that has quietly moved in around it.