Burrowing Owl Mitigation on Project Sites: Current Approaches and Impending Changes

Author: Michael Tuma

Burrowing owls (Athene cunicularia), an at-risk species, are increasingly becoming an issue for projects implemented in California. This is particularly the case for projects implemented in areas supporting grasslands or desert scrub communities that are inhabited by burrowing wildlife and contain burrows suitable for use by burrowing owls. The burrowing owl is considered a Species of Special Concern by the California Department of Fish and Wildlife (CDFW) and a Bird of Conservation Concern by the U.S. Fish and Wildlife Service (USFWS). The active nests of burrowing owls are protected under the federal Migratory Bird Treaty Act (MBTA) and California Fish and Game Codes. In March of 2024, several conservation groups petitioned the California Fish and Game Commission to list the species under the California Endangered Species Act. If the Commission votes to list the species, additional protections will apply to projects and activities that have the potential to take burrowing owls, and current management protocols for burrowing owls on project sites would likely change.  

The current management approach in California is driven largely by the CDFW (2012) Staff Report on Burrowing Owl Mitigation and by Multiple Species Habitat Conservation Plans (MSHCPs), namely the Western Riverside County MSHCP and Coachella Valley MSHCP in southern California. CDFW also regulates burrowing owl protections through California Fish and Game Code Sections 3503, which prohibits the take or destruction of bird nests, 3503.5, which prohibits the take or destruction of hawk, falcon, eagle, osprey, and owl nests, and 3513, which prohibits take of species protected under the MBTA. The MBTA, which is enforced by the USFWS, prohibits the taking of migratory birds and their nests, eggs, and young. The CDFW (2012) Staff Report on Burrowing Owl Mitigation provides guidelines for conducting habitat assessments, protocol presence/absence surveys, project impact assessments, and passive eviction of burrowing owls from project sites. Biological consultants regularly employ these techniques to support projects and to ensure that project impacts to burrowing owls are avoided, minimized, and/or mitigated. 

The Burrowing Owl

Burrowing owls are relatively small owls in the family Strigidae that, unlike other owls, inhabit and breed in subterranean burrows. Burrowing owls rarely excavate their own burrows but rather occupy and modify burrows excavated by other fossorial species, such as California ground squirrels (Otospermophilus beecheyi), desert kit foxes (Vulpes macrotis arsipus), coyotes (Canis latrans), American badgers (Taxidea taxis), or Mojave Desert tortoises (Gopherus agassizii). Burrowing owls may also find cover in anthropogenic cover sites, such as piles of rubble or concrete slabs, pipes, culverts, or under large pieces of trash, debris, or other structures or materials. 

Burrowing owls prefer open areas with sparse, low-statured vegetation such as grasslands and desert scrublands. Inhabiting such areas allows burrowing owls to see potential predators from the ground surface or low perch, and to hunt for food. 

Burrowing owls nest within burrows, and their nesting season is generally between late January through August or September. Female burrowing owls lay between 2 and 12 eggs over a period of several days. The eggs are incubated for about 30 days before hatching. The young fledge in about 50 days, but they may be dependent on the adults for food for an extended period following fledging. Young burrowing owls are particularly vulnerable to predation and typically not all chicks from a nest may survive to adulthood. 

Burrowing owls are active and hunt primarily at night and during dawn and dusk hours, but may be active throughout the day, particularly if conditions are mild. During their daily activity, they hunt arthropods such as spiders, beetles, crickets, grasshoppers, and small rodents, reptiles, and birds. They hunt on the ground surface or within low vegetation but can also capture prey mid-air during flight. Most of their foraging activities occur within 600 meters of their burrows. 

Burrowing owls are yearlong residents in California that typically make short-distance movements between breeding and wintering areas, with fidelity to previously used breeding areas. Owls in some populations do not migrate and remain in breeding areas year-round. The population of burrowing owls in California swells during the winter when individuals from northern areas outside of the state migrate to California. 

Within California, burrowing owls are most common in southern California, particularly in the Colorado (low) and Mojave (high) Deserts. The highest densities of burrowing owls are in the Imperial Valley, where they inhabit agricultural fields. They are also commonly found throughout the Inland Empire of southern California and the Central Valley. They may also occur, though less commonly, in coastal valleys of southern California. There is a small population near San Jose in the San Francisco Bay area. 

Burrowing owl populations in California are threatened primarily by habitat loss due to human development and land use. They prefer to inhabit lowland areas, typically 60 to 300 meters in elevation, which are areas that are under the most severe pressure from urban development, agricultural production, and other anthropogenic land uses. Other threats to burrowing owls include pesticide use, ground squirrel eradication programs, predation by subsidized predators such as common ravens (Corvus corax) and coyotes, livestock grazing, and vehicle strikes, among others.  

Currently, to ensure that project activities avoid impacts to burrowing owls, FirstCarbon Solutions (FCS) biologists perform habitat assessments, protocol breeding season and non-breeding season surveys, pre-construction surveys, and – when owls are detected – prepare and implement Burrowing Owl Mitigation Plans to monitor breeding burrowing owls and passively evict non-breeding owls from project sites.

Burrowing Owl Habitat Assessments

For projects implemented within the range of the burrowing owl in California, the first step to determine if they occupy the project site is to conduct a habitat assessment. During a habitat assessment, a qualified biologist will walk the project site and map areas of suitable habitat on-site and within 500 feet of the project boundary, as the implementation of the project could affect owls inhabiting adjacent areas. Areas mapped with suitable habitat would include grasslands, sparse scrublands, and agricultural fields, particularly if they are allowed to go fallow and bare or ruderal areas. If the biologist detects burrows suitable for occupancy by burrowing owls within areas of mapped habitat, the value of that habitat increases, as does the potential for burrowing owls to occur on-site. Following the habitat assessment, the biologist will detail the results in a Burrowing Owl Habitat Assessment Report. If suitable habitat is present on or adjacent to the project site, the biologist will recommend that focused surveys be conducted for burrowing owls, per CDFW (2012) Staff Report protocol.  

Protocol for Burrowing Owl Surveys 

Focused surveys for burrowing owls, per CDFW (2012) Staff Report protocol, consist of a series of four site visits to search for burrows and burrowing owls within mapped suitable habitats. The surveys may be implemented during the breeding season (Breeding Season Surveys) or outside of the breeding season (Non-Breeding Season Surveys). CDFW typically requires that Breeding Season Surveys are implemented prior to project development; however, if time allows it, conducting Non-Breeding Season Surveys can provide additional information about the use of the site by burrowing owls outside of the breeding season. During a focused survey, a qualified biologist will search for and map burrows during the first site visit and search for and document burrowing owls during the subsequent three site visits. To maximize the potential for detecting owls, biologists will conduct searches when owls are most active above ground, which is near sunrise and sunset, and during appropriate weather conditions. The biologist will not only search for burrowing owls but also evidence that owls have occupied burrows. Evidence that burrowing owls have occupied a burrow includes the presence of owl ‘sign’ around the burrow entrance, including uric acid excrement or “whitewash,” pellets regurgitated from the owls’ gizzards, tracks, feathers, and leftover food, such as rodent or reptile carcasses. If burrowing owls are detected during the surveys, the biologist will determine whether they are solitary or paired and, if the survey is conducted during the breeding season, whether evidence of breeding is discernable. The locations of suitable burrows, occupied burrows, and burrowing owls will be recorded by the biologist and provided in the survey report.  

Another protocol survey often required for projects that support burrowing owl habitat is a pre-construction survey. These surveys are typically completed immediately prior to the initiation of ground-disturbing or vegetation-removing construction activities on a project site, such as clearing and grubbing. Per the CDFW (2012) Staff Report protocol, the pre-construction surveys are implemented over two site visits, one 14 days prior to the planned initiation of construction activities and one 24 hours prior. During the surveys, the biologist will survey suitable habitat on and adjacent to the project site to search for burrowing owls and follow up with a Burrowing Owl Pre-Construction Survey Report after the final survey. 

If either the focused surveys or pre-construction surveys are positive for burrowing owl the project will be required to develop and implement a Burrowing Owl Mitigation Plan, per CDFW (2012) Staff Report protocol. If both the focused surveys and the pre-construction survey are negative for burrowing owl, the project may proceed without a mitigation plan.   

Burrowing Owl Mitigation Plans

When burrowing owls are detected on a project site, the applicant must prepare and submit a Burrowing Owl Mitigation Plan to CDFW prior to construction. The plan will provide details about burrowing owl occupancy of the project site, an assessment of project impacts to burrowing owls and their habitat, and a plan for mitigating or avoiding impacts. For project impacts to habitat occupied by burrowing owls, purchase of off-site mitigation lands or credits may be required. If the project is in the Western Riverside County MSHCP or Coachella Valley MSHCP plan areas, take of burrowing owl habitat is covered through payment of a per-acre MSHCP fee, and off-site mitigation would not be required. Project impacts to burrowing owls, whether the project is in an MSHCP area or not, would need to be avoided or mitigated.  

To maintain project compliance with the federal MBTA and California Fish and Game Code Sections that protect nesting birds, avoidance of burrowing owl nesting burrows is the only option available for the project applicant. Per the CDFW (2012) Staff Report protocol, avoidance of burrowing owls is accomplished through the establishment of avoidance buffers around occupied burrows within which no project activities may occur. Depending on the level of disturbance caused by project activities and the time of year, avoidance buffers of between 50 and 500 meters may be required. The most restrictive buffers would be implemented around nesting burrows during the peak of breeding season. Smaller buffer sizes may be an option if the project is located within an MSHCP plan area that defines avoidance buffer sizes. The Burrowing Owl Management Plan will provide options for establishing avoidance buffers that draw upon project conditions and proposed activities, time of year in relation to the burrowing owl breeding season, whether the project is located within an MSHCP plan area, and whether visual screening will be employed to shield project activities from view of the owls. The buffers are maintained, and work activities are prohibited within them until the nesting season is concluded, which is determined by a qualified biologist when there is evidence that the young are no longer dependent on receiving food from the adults and are foraging on their own. 

Outside of the nesting period, project applicants can evict burrowing owls from the project site and close the burrows, which allows for the removal of avoidance buffers and implementation of project activities in the formerly occupied area. The nesting period is defined by the CDFW (2012) Staff Report as February 1 through August 31, but it may begin earlier if there is evidence of breeding behaviors in late January or evidence that young are still dependent on adults into September or October. The Burrowing Owl Mitigation Plan will outline a plan for eviction that accounts for conditions on and adjacent to the project site, the number of owls occupying the site, and whether owls have recently used the site for breeding. The eviction plan will outline methods for tracking owl activity, verifying occupied and unoccupied burrows on and off-site, installing one-way doors on burrows and evicting owls, closing on-site burrows, and monitoring owls following eviction. If natural burrows suitable for burrowing owl occupancy are not available in adjacent, off-site areas, the Burrowing Owl Mitigation Plan may include instructions for the construction of artificial burrows. Other aspects that may be incorporated into the plan include the use of wildlife cameras to monitor occupied burrows, continuous monitoring by biologists to track owl activities, and reporting to lead and/or responsible agencies before, during, and/or after the eviction effort.  

Impending Decision on The California Endangered Species Act Listing

In March 2024, several groups (Center for Biological Diversity, Defenders of Wildlife, Burrowing Owl Preservation Society, Santa Clara Valley Audubon Society, Urban Bird Foundation, Central Valley Bird Club, and San Bernardino Valley Audubon Society) petitioned the California Game and Fish Commission to list the burrowing owl under CESA. The petitioners presented evidence that the species has been extirpated from 19 counties in California and that populations have declined significantly in 10 other counties. They requested that the Commission consider listing three populations (San Francisco Bay Area, Central-Western California, and Southwestern California) as Endangered and two populations (Central Valley and Southern Desert Range) as Threatened, or alternatively to consider listing the species as Threatened statewide. In late July 2024, CDFW released its evaluation of the petition and recommended that the Commission accept the petition for further consideration and advance the burrowing owl to Candidate status under CESA. They also provided recommendations in their evaluation that offer clues as to how CDFW may manage the species if it becomes covered or listed under CESA. These include updating the survey guidelines in the CDFW (2012) Staff Report protocol to reflect the latest scientific information and making the survey and mitigation recommendations provided therein mandatory for projects; limiting the use of passive eviction that is currently allowed under the protocol; strengthening requirements for mitigating project impacts to breeding owls and their habitat; increasing enforcement of California Fish and Game Code Sections that protect burrowing owl nests; and reviewing existing Habitat Conservation Plans / Natural Community Conservation Plans such as the Western Riverside County and Coachella Valley MSHCPs to ensure that they are ‘adequately protective’ – likely meaning that the burrowing owl conservation requirements under these plans may be made consistent with not only the current CDFW (2012) Staff Report but also any new updates to this guidance.  

The recommendation from CDFW does not necessarily mean that the Burrowing owl will be listed. The Commission rejected a previous petition to list the species in 2003. The Commission will consider the recommendation on the current petition at their October 10, 2024, meeting. If the Commission votes to accept the petition and advances the burrowing owl to Candidate status, the species would immediately be afforded the same protections as a listed species throughout the 12-18 months it is expected to take for the Commission to make a final determination. Advancement of the species to Candidate status would have significant consequences for permitting project impacts to burrowing owls. The biggest change would involve obtaining take authorization through the issuance of an Incidental Take Permit (ITP) by CDFW under the CESA process. ITPs would likely require the purchase of off-site lands to offset the loss of occupied burrowing owl habitat on project sites. The availability and acquisition of off-site lands for such mitigation may be an issue until CDFW-approved conservation banks are established. Burrowing Owl Mitigation Plans would still likely be required but would be reviewed and processed by CDFW staff from the Habitat Conservation and Planning Branch. Certainly, breeding season avoidance of nesting burrows would continue to be required, as there is no taking of nests authorized under the MTBA or California Fish and Game Code Sections pertaining to the protection of nesting birds, and these forms of take are not permitted under CESA. Non-breeding season owl evictions, if allowed under the ITP process, will likely be implemented differently and under more restrictive conditions than are currently allowed under the CDFW (2012) Staff Report protocols. Initiating work on project sites could potentially become very difficult during the burrowing owl breeding season, as the recommendation for 500-meter buffers around nesting burrows in the CDFW (2012) Staff Report protocols would likely become mandatory, which would render significant portions of project sites unavailable for development. Together, these issues could potentially make development of project sites in burrowing owl habitat more difficult despite there being a process in place for take.  

If a project site supports burrowing owl habitat or other protected species, FCS can step in to skillfully handle habitat assessments, protocol surveys, and planning and implementation of mitigation programs. Should the burrowing owl be advanced to Candidate status or listing under CESA, FCS also has the expertise to guide clients through the ITP process and successfully secure project and permit approval, ensuring that projects proceed efficiently. 

FCS, an ADEC Innovation, comprises more than 100 individuals offering due diligence, technical analysis, planning, environmental compliance, permitting, and mitigation/monitoring services for both public and private projects. FCS has more than 30 years of experience navigating environmental regulatory complexities. Contact us for a free consultation.