SPECIES NAME AND GROUP DESIGNATION

Common Name and Scientific Name:

coastal California gnatcatcher (Polioptila californica californica)

Status:

State: Species of Special Concern (full species)

Federal: Threatened

GROUP DESIGNATION AND RATIONALE

Group 2

The coastal California gnatcatcher is distributed widely within suitable habitat in the Riverside lowlands and San Jacinto Foothills Bioregions especially along the Interstate 15/215 corridor from the Santa Ana River to Temecula and into the Vail Lake area. It is absent from the higher elevations and desert areas. The Coastal California gnatcatcher occurs in 16 Core Areas within the Plan Area including Alessandro Hills, El Cerrito, Lake Mathews-Estelle Mountain Reserve, Alberhill area, the proposed North Peak Conservation Bank/Meadowbrook area, Wasson Canyon, Railroad Canyon, Quail Valley, Sedco Hills, Hogbacks, Murrieta Hot Springs, Lake Skinner, Buck Road to Pourroy Road east of Murrieta Hot Springs, Vail Lake/Wilson Valley including the eastern Temecula Creek area, Rancho California east of Interstate 15 to De Portola Road, and Norco Hills. The coastal California gnatcatcher, as a year-round resident, has lower dispersal capabilities than small passerine birds that are long-distance migrants and thus relies on habitat linkages for localized and regional movements. Because the coastal California gnatcatcher is well known for using coastal sage scrub within the lowland and foothill Bioregions, occurs widely within its suitable habitat, but has specific locations that are Core Areas, it is included as a group 2 species to be managed at a habitat level with site specific requirements in Core Areas and linkages.

SPECIES CONSERVATION OBJECTIVES

The species-specific conservation objectives developed for this species are based upon the best available scientific information existing at the time of MSHCP preparation. Pursuant to the Adaptive Management Program, the MSHCP's mitigation requirements will be monitored and analyzed to determine if they are producing the desired result. Based upon this information, the following species-specific conservation objectives may be adjusted as new information is gathered during Plan implementation. The Adaptive Management Program will be used to identify alternative strategies for meeting the MSHCP's general biological goals and objectives and if necessary, adjusting future conservation strategies according to the information received.

Objective 1

Include within the MSHCP Conservation Area at least 77,070 acres of suitable habitat including coastal sage scrub, Riversidean alluvial fan scrub and desert scrub in the Riverside Lowland and San Jacinto Foothills Bioregions.

Objective 2

Include within the MSHCP Conservation Area at least 13 of the Core Areas and interconnecting linkages within 9 Core and Linkage areas including El Cerrito/Lake Mathews-Estelle Mountain Reserve (Existing Core C plus Proposed Extension of Existing Core 2; 23,710 acres), Alberhill area (Subunit 2 of the Elsinore Area Plan; 3,460 acres), the proposed North Peak Conservation Bank/Meadowbrook area (Subunit 6 of the Elsinore Area Plan; 1,080 acres), Wasson Canyon (Subunit 5 of the Elsinore Area Plan; 2,320 acres), Railroad Canyon/Sedco Hills (Proposed Linkage 8; 5,470 acres), a portion of the Quail Valley area (Proposed Linkage 7; 3,400 acres), Hogbacks/Murrieta Hot Springs (Proposed Core 2 plus Existing Constrained Linkage A; 5,350 acres), Lake Skinner/Buck Road to Pourroy Road east of Murrieta Hot Springs (Existing Core J plus Proposed Extension of Existing Core 5, 6, and 7; 29,060 acres), Vail Lake/Wilson Valley including the eastern Temecula Creek area (Proposed Core 7; 50,000 acres). Due to mapping configuration, some of the coastal California gnatcatcher Core Areas have been combined in order to provide the acreage of MSHCP Conservation Area within the Core Area.

Objective 3

Within the MSHCP Conservation Area, maintain (once every three years) continued use of and successful reproduction at 75 percent of the Core Areas. Successful reproduction is defined as a nest which fledged at least one known young.

SPECIES CONSERVATION ANALYSIS

Conservation Levels

The primary habitat for the coastal California gnatcatcher includes coastal sage scrub, desert scrubs, and Riversidean alluvial fan scrub within the Riverside lowlands and San Jacinto foothills Bioregions. Frequently, pockets of coastal sage are located within a matrix of chaparral or grassland areas and these pockets may be occupied. In addition, gnatcatchers occupy other secondary habitats (i.e., chaparral, grasslands, riparian). These secondary habitats may be important as nesting, foraging, and/or dispersal areas, however, only a small proportion of these habitats are occupied and, therefore, only primary habitat is used for the purpose of the conservation analysis (although some unquantified additional conservation value will be provided by the conservation of secondary habitats within the Core Areas and linkages within the MSHCP Conservation Area). The Plan Area supports approximately 140,770 acres of primary habitat for the coastal California gnatcatcher. Table 1 shows the conservation and loss of primary habitat for the coastal California gnatcatcher. A total of 77,070 acres (55 percent) of the primary habitats, coastal sage scrub, desert scrubs, and Riversidean alluvial fan scrub habitats, are conserved within Criteria Area and Public/Quasi-Public Lands.

As part of 1995 PSBS/KTU+A work referenced in the discussion of MSHCP vegetation (MSHCP Chapter 2), PSBS and KTU+A modeled and evaluated variables potentially relevant to the suitability of coastal sage scrub habitat within the Plan Area for the coastal California gnatcatcher. A detailed description of the methodology used to develop the model is presented in their report (PSBS and KTU+A, 1995). The 1995 PSBS/KTU+A work was designed to gather and organize existing information on current and future land uses, identify gaps of information, and evelope tools to evaluate potential alternative reserve designs focused on doastal sage scrub and coastal California gnatcatchers. Variables considered included elevation, slope, patch size, patch shape, proximity to other coastal sage scrub patches, isolation of patches and adjacent land use. The modeling results labeled areas as very high, high, moderate, low and very low with respect to the quality of coastal sage scrub. A total of 104,820 acres of moderate, high, and very high quality coastal sage scrub habitat (PSBS and KTU+A 1995) is present within the Plan Area. These three categories of the habitat quality mapping overlap with the all of the Core Areas of the coastal California gnatcatcher. The high and very high quality coastal sage scrub categories overlap with all of the core population areas except for that in the Hogbacks and Rancho California areas and portions of the Murrieta Hot Springs and Buck Road to Pourroy Road east of Murrieta Hot Springs areas. A total of 64,010 acres (61 percent) of moderate, high and very high quality of coastal sage scrub habitat (based on mapping in PSBS and KTU+A 1995) is conserved within Criteria Area or Public/Quasi-Public Lands. This includes 14,460 acres (80 percent) of the very high quality habitat, 30,700 acres (58 percent) of the high quality habitat, and 16,350 acres (48 percent) of the moderate quality habitat.

TABLE 1
SUMMARY OF HABITAT CONSERVATION
COASTAL CALIFORNIA GNATCATCHER

As described below under Data Characterization, 391 of the 521 point localities within the UCR database have a high location precision. Of these 391 point localities, 234 (60 percent) will be inside the Criteria Area or Public/Quasi-Public Lands. A total of 27 (7 percent) will be in the Rural/Mountainous zone. However, of the 130 (33 percent) points located outside these habitat areas, 37 are mapped in existing residential/urban/exotic areas.

As indicated above, there are definable locations for focusing conservation efforts (i.e., Core Areas for the coastal California gnatcatcher and the linkage areas between the cores). These areas include El Cerrito, Lake Mathews-Estelle Mountain Reserve, Alberhill area, the proposed North Peak Conservation Bank/Meadowbrook area, Wasson Canyon, Railroad Canyon area, a portion of the Quail Valley area, Sedco Hills, Hogbacks, Murrieta Hot Springs, Buck Road to Pourroy Road east of Murrieta Hot Springs, Lake Skinner, and Vail Lake/Wilson Valley including the eastern Temecula Creek area. These Core Areas have been combined in some cases and are reflected by the acreage calculated for each core as follows: El Cerrito/Lake Mathews-Estelle Mountain Reserve (Existing Core C plus Proposed Extension of Existing Core 2; 23,710 acres), Alberhill area (Subunit 2 of the Elsinore Area Plan; 3,460 acres), the proposed North Peak Conservation Bank/Meadowbrook area (Subunit 6 of the Elsinore Area Plan; 1,080 acres), Wasson Canyon (Subunit 5 of the Elsinore Area Plan; 2,320 acres), Railroad Canyon/Sedco Hills (Proposed Linkage 8; 5,470 acres), a portion of the Quail Valley area (Proposed Linkage 7; 3,400 acres), Hogbacks/Murrieta Hot Springs (Proposed Core 2 plus Existing Constrained Linkage A; 5,350 acres), Lake Skinner/Buck Road to Pourroy Road east of Murrieta Hot Springs (Existing Core J plus Proposed Extension of Existing Core 5, 6, and 7; 29,060 acres), Vail Lake/Wilson Valley including the eastern Temecula Creek area (Proposed Core 7; 50,000 acres). The total Core Area acreage conserved within the MSHCP Conservation Area is 123,850 acres. The three core population areas not proposed for conservation (Alessandro Hills, Norco Hills, and Rancho California east of Interstate 15 to De Portola Road) within the MSHCP Conservation Area are generally located within very constrained areas that have already been highly developed. These areas consist of fragmented, small patches of coastal sage scrub habitat. The patches have very high edge effects and some of the point locations have been lost to development.

MSHCP Conservation Area Configuration Issues

Several large blocks of habitat supporting the coastal California gnatcatcher will be conserved as Criteria Area and Public/Quasi-Public Lands including the Core Areas at El Cerrito, Lake Mathews-Estelle Mountain Reserve, Alberhill area, the proposed North Peak Conservation Bank/ Meadowbrook area, Wasson Canyon, Railroad Canyon, a portion of the Quail Valley area, Sedco Hills (relatively low number of gnatcatchers but important for the reserve configuration), Hogbacks, Murrieta Hot Springs, Lake Skinner, Buck Road to Pourroy Road east of Murrieta Hot Springs, and Vail Lake/Wilson Valley including the eastern Temecula Creek area. Other locations occupied by the coastal California gnatcatcher but not constituting a Core Area that will be conserved include Sycamore Canyon Regional Park, portions of Temecula west of Interstate 15, and the Badlands.

Areas that are important for preservation for dispersal purposes but that may not contain large numbers of gnatcatchers include several areas that provide essential connections outside of the Plan Area to other populations of the coastal California gnatcatcher. Conservation of areas within the Jurupa Mountains, Pigeon Pass Road area, San Timoteo Creek and the Badlands provide connectivity into San Bernardino County. Conservation of areas in the Cleveland National Forest near the 91 Freeway and Chino Hills area provide connectivity into Orange County. Conservation within the Santa Rosa Plateau Nature Reserve, Santa Margarita Ecological Reserve, and Aguanga area provide connection into San Diego County.

Within the Plan Area there are also large areas conserved that may provide dispersal corridors but that do not contain large number of gnatcatchers. Conservation of the foothills of the Santa Ana Mountains within Cleveland National Forest is provided west of Interstate 15 which provides a broad area for dispersal on the west side of Interstate 15. Conservation of riparian habitat from the Prado Basin along the Santa Ana River provides a linkage that may not be used consistently but that is composed of habitat that the coastal California gnatcatcher has been documented to use occasionally and could use for dispersal.

Conservation of both Core Areas in the form of large blocks of habitat, as described above, as well as narrower linkages for movements between the core population areas is essential for the MSHCP Conservation Area configuration and conservation strategy. Although the gnatcatcher is not as adept at dispersing as some of the long distance migrant bird species, it has been documented to disperse at least 1.1 kilometers (Galvin 1998). Based on observations of coastal California gnatcatchers in a variety of natural and non-natural habitats, it is expected that they may disperse across marginal habitats such as agriculture, disturbed habitats (e.g., fallow fields, abandoned vineyards) and non-native grasslands and are capable of moving across roadways. As much as possible, it is recommended that linkages be as wide as a gnatcatcher territory within the Western Riverside County area, which has been estimated at approximately 400 meters (approximately 1,200 feet), feet based on the diameter of an average territory. Generally, in order to protect against adverse edge effects, it is better for the linkage to be wider than 400 meters (approximately 1,200 feet), however, some areas are currently constrained and for short distances, narrow linkages or stepping stone reserves will be required.

As such, the MSHCP Conservation Area will provide adequate habitat linkages between Core Areas for this species. Linkage widths in the Home Gardens area south to the El Cerrito Core Area are approximately 0.8 to 1.2 kilometers wide. The El Cerrito, Lake Mathews-Estelle Mountain Reserve, and Alberhill Core Areas are contained within a large block of contiguous habitat that at its narrowest is approximately 1.7 kilometers in width. The connection between the Alberhill Core Area and the North Peak Conservation Bank/Meadowbrook area is a narrow (approximately 0.4 kilometers) but relatively short constrained connection of approximately 2 kilometers in length. At that, the linkage is still the minimum width of a territory diameter. The connection between the North Peak conservation Bank Core Area and the Wasson Canyon Core Area also is narrow but also is very short (0.4 kilometer for 0.8 kilometer). The portion of the Quail Valley Core Area that is conserved is well connected to the Wasson Canyon area with the conservation in BLM parcels and Kabian Park. Similar to the North Peak connection to Wasson Canyon, the Wasson Canyon Core Area has a narrow but short linkage to the Railroad Canyon Core Area. This linkage is approximately 0.3 kilometer wide for approximately 0.5 kilometer in length. The Sedco Hills Core Area is a long habitat patch that varies in width from 0.8 kilometer to 1.7 kilometers in width with one pinch point of approximately 0.4 kilometer.

The Sedco Hills Core Area is separated from the Hogbacks area by Interstate 215, however a narrow linkage is provided via a drainage approximately half-way between Scott Road and Clinton Keith Road. This linkage is approximately 0.4 kilometer wide for approximately 0.8 kilometer. The Hogbacks Core Area is a large habitat block that is connected to the Lake Skinner large habitat block and the Buck Road to Pourroy Road large habitat block by narrow linkages that are currently constrained by existing development. These linkages are located within drainages and are provided as more than one linkage to provide for duplicity of connections. These linkages are within the Warm Springs drainage, Tucalota Creek, and Santa Gertrudis Creek. The Lake Skinner Core Area is linked to the Vail Lake/Wilson Valley including the eastern Temecula Creek Core Area by preservation east of Lake Skinner along Tucalota Creek in a 0.8 to 1.25 kilometer linkage. A very large block of habitat is conserved in the Vail Lake/Wilson Valley including the eastern Temecula Creek area which adjoins the San Bernardino National Forest to the east and to the Cleveland National Forest to the south.

Stepping stone reserves conserve some locations of gnatcatchers and connect some of the smaller numbers of Coastal California gnatcatchers which do not comprise core populations including: Sycamore Canyon Regional Park which is connected by Box Springs Mountains to Highgrove by either very narrow drainages or stepping stone reserve and also is connected by stepping stone reserves through the Alessandro Hills and Mockingbird Canyon through wetlands preservation to El Cerrito.

The conservation strategy and MSHCP Conservation Area design for the gnatcatcher takes into account that large scale fires damage gnatcatcher habitat for a relatively long length of time and large areas are necessary to provide refugia for birds and to supply dispersing individuals to a recovered area for re-population. Within the Plan Area, the Alberhill Core Area is separated from other Core Areas by an existing firebreak in the form of the I-15 freeway corridor. Thus, if a wildfire occurs east or west of I-15, the population on the opposite side of the freeway will likely be protected. Duplicate linkages also provide for the temporary loss of function of the coastal sage scrub habitat in the event of a fire (Campbell et al. 1998). A duplicity of habitat linkages composed of sage scrub and other undeveloped habitats which may be composed of native as well as non-native habitats may provide for dispersal ability of the species (Campbell et al. 1998). Several duplicate linkages are preserved within the MSHCP Conservation Area. Between the Hogbacks and Core Areas at Lake Skinner and AD161 area, a network of linkages is designed. Several linkages occur between the Core Areas on the east side of Interstate 15 and the west side to the Cleveland National Forest at Indian Canyon and Horsethief Canyon.

Conservation Summary

In summary, conservation for this species will be achieved by inclusion of at least 77,070 acres of suitable Conserved Habitat and 13 Core Areas within large blocks of habitat in the MSHCP Conservation Area. In addition, implementation of Objective 3 for this species will document that the MSHCP Conservation Area will maintain (once every three years) the continued use of and successful reproduction at 75 percent of the Core Areas. Successful reproduction is defined as a nest which fledged at least one known young.

The current number of locations of the gnatcatcher in Riverside County is estimated at 250 to 300 pairs. The gnatcatcher is restricted to more lowland areas and is not distributed evenly through the preferred habitat. It occurs in a patchy distribution and thus the suitable habitat as well as the Core Areas and connections of these Core Areas need to be addressed as described in detail above. Numerous small patches and small numbers of gnatcatchers are conserved as well and are likely to be important as providing a source of dispersing birds. These small populations, many of which are documented above to be preserved may be important to prevent further isolation of remaining breeding groups.

INCIDENTAL TAKE

About 63,700 acres of potential primary habitat for the coastal California gnatcatcher will be outside the Criteria Area and Public/Quasi-Public designations, or about 45 percent of the total potential primary habitat. Of this, approximately 19,940 acres (14 percent) of potential primary habitat is located within Rural/Mountainous designation areas. Based on the evaluation of habitat quality provided by PSBS and KTU+A (1995), approximately 40,810 acres (39 percent) of moderate, high and very high quality habitat will be outside the MSHCP Conservation Area. This includes 3,470 acres (19 percent) of the very high quality habitat, 20,680 acres (39 percent) of the high quality habitat, and 16,660 acres (49 percent) of the moderate quality habitat.

Core areas not conserved within Criteria Area and Public/Quasi-Public designations include the Norco Hills population (approximately 5 locations), Alessandro Hills (approximately eight locations), a portion of the Quail Valley area (approximately six locations), and Rancho California east of Interstate 15 to De Portola Road (approximately 10 locations some of which may no longer be extant due to recent development in the area). Based on the UCR database, a total of 27 locations (7 percent) will be in the Rural/Mountainous zone and 130 locations (33 percent) are located outside the MSCHP Conservation Area. However, of the 130 points, 37 are mapped in existing residential/ urban/exotic areas.

SPECIES ACCOUNT

Data Characterization

The location database for the coastal California gnatcatcher contains approximately 521 data points which range in the date of the location point from 1888 to 1999. Approximately 391 data records are of a high degree of precision and will be useful for analysis although many of these point locations could represent duplicate counts for areas that were surveyed in the early 1990s and then surveyed again. The database indicates that there is an adequate amount of information regarding the overall population size and that patterns of occurrences represent areas of use. The habitats represented in these recent and high precision records include coastal sage scrub, chaparral, grassland, alluvial fan scrub, residential or developed, reservoir, agriculture land, and two within riparian or oak woodland habitat. Approximately324 of the recent data records are of a high precision, currently located within Riversidean sage scrub/grassland/chaparral habitats from the vegetation overlay for the Plan Area. Thus, these points are likely to be extant. Approximately 50 of the more recent (1990 or later) and high precision location code data points are overlain with residential/urban/exotic vegetation types and likely no longer exist.

Due to the recent listing and various federal actions regarding the coastal California gnatcatcher and the location within a rapidly developing area of the United States, as well as the controversy that has surrounded the listing of the species, the coastal California gnatcatcher has been well studied by the scientific community and the available literature on the species is very large ( USFWS 1991; USFWS 1993; USFWS 1995; USFWS 1996; USFWS 1999; USFWS 2000) . The literature includes studies on the natural history, habitat requirements, management implications and recommendations. The gnatcatcher has been well studied in western Riverside county mainly due to the establishment of the Southwestern Riverside County Multiple Species Reserve and the accompanying management fund. In addition there is an excellent baseline for the distribution of the gnatcatcher populations within the Plan Area boundary.

Habitat and Habitat Associations

The coastal California gnatcatcher (gnatcatcher), a subspecies of the California gnatcatcher, is a small member of the thrush family (Muscicapidae). The gnatcatcher typically occurs in or near sage scrub habitat, which is a broad category of vegetation that includes the following plant communities as classified by Holland (1986): Venturan coastal sage scrub, Diegan coastal sage scrub, maritime succulent scrub, Riversidean sage scrub, Riversidean alluvial fan sage scrub, southern coastal bluff scrub, and coastal sage-chaparral scrub. Coastal sage scrub is composed of relatively low-growing, dry-season deciduous, and succulent plants. Characteristic plants of this community include California sagebrush (Artemisia californica), various species of sage (Salvia sp.), California buckwheat (Eriogonum fasciculatum), lemonadeberry (Rhus integrifolia), California encelia (Encelia californica), and Opuntia spp. Ninety-nine percent of all gnatcatcher locality records occur at or below an elevation of 984 feet (Atwood 1990).

Coastal sage scrub is patchily distributed throughout the range of the gnatcatcher, and the gnatcatcher is not uniformly distributed within the structurally and floristically variable coastal sage scrub community. Rather, the subspecies tends to occur most frequently within the California sagebrush-dominated stands on mesas, gently sloping areas, and along the lower slopes of the coast ranges (Atwood 1990). An analysis of the percent gap in shrub canopy supports the general impression that gnatcatchers prefer relatively open stands of coastal sage scrub (Bontrager 1991). The gnatcatcher occurs in high frequencies and densities in scrub with an open or broken canopy while it is absent from scrub dominated by tall shrubs and occurs in low frequencies and densities in low scrub with a closed canopy (Weaver 1998). The territory size increases as vegetation density decreases and with distance from the coast, probably due to food resource availability. Thus, gnatcatchers will use even sparsely vegetated coastal sage scrub for shelter and to forage for insects as long as perennial shrubs are available (ERCE 1990).

Gnatcatchers also use chaparral, grassland, and riparian or alluvial habitats where they occur adjacent to sage scrub (Bontrager 1991). The use of these habitats appears to be most frequent during late summer, autumn, and winter, with smaller numbers of birds using such areas during the breeding season. These non-sage scrub habitats are used for dispersal, but data on dispersal use are largely anecdotal (Bowler 1995; Campbell et al. 1995). Although existing quantitative data may reveal relatively little about gnatcatcher use of these other habitats, these areas may be critical during certain times of the year for dispersal or as foraging areas during drought conditions (Campbell et al. 1998). Breeding territories have also been documented in non-sage scrub habitat. Campbell et al. (1998) discuss likely hypotheses explaining why non-CSS habitat is used by gnatcatchers including food source availability, dispersal areas for juveniles, temperature extremes, fire avoidance, and lowered predation rate for fledglings.

Environmental, vegetational, and food-abundance characteristics are important aspects of territory quality, however, they are related to the time of year when the evaluation is made (Redak et al. 1997). Based on the studies of Redak et al. (1997) during the breeding season, habitat use was negatively associated with distance to the coast and the elevation of the territory. The habitat use was positively associated with the abundance of adult stages of beetles, flies, spiders and larval stages of all arthropods. Plots with high densities of California sagebrush, flat-topped buckwheat, and white sage were also used by birds. In contrast, during the nonbreeding season, the correlation of habitat use with vegetation and location variables remained but the correlation was no longer present with the arthropod communities.

Biogeography

Historically, gnatcatchers occurred from southern Ventura County southward through Los Angeles, Orange, Riverside, San Bernardino, and San Diego counties, and into Baja California, Mexico, to approximately 30 degrees north latitude near El Rosario (Atwood 1990). A detailed analysis of elevational limits associated with gnatcatcher locality records reveals that a significant portion, 65 to 70 percent of the historic range, may have been located in southern California rather than Baja California (USFWS 2000). The gnatcatcher was considered locally common in the mid-1940's, but by the 1960's this subspecies had declined substantially in the United States owing to widespread destruction of its habitat (Atwood 1990). Currently, the subspecies occurs on coastal slopes of southern California, ranging from southern Ventura southward through Palos Verdes Peninsula in Los Angeles County through Orange, Riverside, San Bernardino and San Diego Counties into Baja California to El Rosario, Mexico, at about 30 degrees north latitude (Atwood 1991). In 1993, the USFWS estimated that approximately 2,562 pairs of gnatcatchers remained in the United States. Of these, 30 pairs occurred in Los Angeles County, 757 pairs occurred in Orange County, 261 pairs occurred in Riverside County, and 1,514 pairs occurred in San Diego County.

Known Populations Within Western Riverside County

The gnatcatcher is found throughout lowland and foothill Bioregions of western Riverside county in coastal sage scrub habitat. The high density areas are found in the western portion of the county along the I-15 corridor continuing east within the southern portion of the Plan Area to Lake Skinner and Vail Lake. The distribution of gnatcatchers in the County does not appear to be uniform along this strip, instead high density patches of several Core Areas exist in generally two locations within the Plan Area, one in the northwestern portion of the Plan Area east of Interstate 15 between Lake Mathews and the City of Lake Elsinore. The other area is in the Murrieta Hot Springs/Lake Skinner area and west to Interstate 215. In 1993, the USFWS estimated the number of pairs of gnatcatchers at 261 (USFWS 1993). Current estimates for gnatcatchers in western Riverside County number around 300 pairs, however the confidence intervals were not reported (USFWS 1996).

From north to south, Core Areas occur at Norco Hills, Alessandro Hills, El Cerrito, Lake Mathews-Estelle Mountain Reserve, Alberhill area, the proposed North Peak Conservation Bank/ Meadowbrook area, Wasson Canyon, Railroad Canyon, Quail Valley, Sedco Hills, Hogbacks, Murrieta Hot Springs, Lake Skinner, Buck Road to Pourroy Road east of Murrieta Hot Springs, Vail Lake/Wilson Valley and eastern Temecula Creek area, and Rancho California east of Interstate 15 to De Portola Road. Other locations with a few gnatcatcher locations but not a key population include Sycamore Canyon Regional Park, Mockingbird Canyon, Temecula west of Interstate 15, and the Badlands.

Biology

Genetics: The coastal California gnatcatcher was originally described as a distinct species by Brewster (1881) based on specimens, however, Grinnell (1926) concluded that it is a subspecies of the black-tailed gnatcatcher (Polioptila melanura) which is widely distributed throughout the Sonoran and Chihuahuan deserts of the southwestern United States and Mexico. Atwood (1980, 1988) concluded that the species was specifically distinct from P. melanura, based on differences in ecology and behavior, which was adopted by the American Ornithologists' Union Committee on Classification and Nomenclature (American Ornithologists Union 1957, 1989). Recent mitochondrial DNA sequencing confirmed the species-level recognition of the Coastal California gnatcatcher, which was calculated to differ from the black-tailed gnatcatcher (P. melanura) by 4.0 percent, similar to differences calculated in the black-capped gnatcatcher (P. nigriceps) and white-lored gnatcatcher (P. albiloris) (Zink and Blackwell 1998).

Diet and Foraging: The coastal California gnatcatcher is primarily insectivorous, nonmigratory, and exhibits strong site tenacity (Atwood 1990). The diet deduced from fecal samples resulted in leaf- and plant hoppers and spiders predominating the samples. True bugs, wasps, bees, and ants were only minor components of the diet (Burger et al. 1999). Gnatcatcher adults selected prey to feed their young that was larger than expected given the distribution of arthropod size available in their environment, and chicks were provisioned with larger prey items and significantly more grasshoppers and crickets and spiders. Both adults and young consumed more sessile than active prey items (Burger et al. 1999).

The richness of the insect community within a habitat area may be a useful tool for describing the quality of the habitat (Burger et al. 1996). This is especially important for strictly insectivorous species such as the coastal California gnatcatcher. Gnatcatcher habitat use has been positively associated with total insect species richness and total individual insect abundance (Redak et al. 1996). Thus overall food abundance and diversity plays an important role in territory selection and use for this species (Redak et al. 1996). Habitat use during the non-breeding season showed no clear relationship to any component of the arthropod community (Redak et al. 1997).

Daily Activity: Activity budget data indicate that gnatcatchers are most active and vocal during the morning. A lull in activity usually occurs during mid-day and activity increases again late in the day (Mock et al., 1990).

Reproduction: The breeding season of the gnatcatcher extends from mid February through mid-August, with the peak of nesting activity occurring from mid-March through mid-May. The gnatcatcher nest is a small, cup-shaped basket usually found one to three feet above the ground in a small shrub or cactus. Clutch sizes range between three and five eggs, with the average being four. Juvenile birds associate with their parents for several weeks (sometimes months) after fledging (Atwood 1990). The coastal California gnatcatcher is a year-round resident. Nest building begins during the mid part of March with the earliest recorded egg date approximately March 20 (Mock et al., 1990). Post-breeding dispersal of fledglings occurs between late May and late November. Predation may be a major source of nest failure (Bontrager 1991; Grishaver et al. 1998). In western Riverside County, 78.9 percent of the nesting attempts failed with 52.9 percent suffering from nest predation (Braden 1999).

Nest site attendance by male gnatcatchers was determined to be equal to that of females for the first nest attempt and then decline to almost 1/3 of that of the female for later nesting attempts (Sockman 1998).

The frequency with which various plant species have been recorded as nesting substrata indicates the overall preference of the sage scrub community as the habitat type (Atwood 1980). California sagebrush was chosen 25 percent of the time with other species including white sage, black sage, chamise, cholla, buckthorn, orange, lemonadeberry, and others making up the balance of nest shrub selections (Atwood 1980).

Survival: Gnatcatchers are persistent nest builders and often attempt multiple broods typically upon nesting failure, which is suggestive of a high reproductive potential. This is, however, typically offset by high rates of nest predation and brood parasitism (Atwood 1990). High rates of nest failure may account for the high number of nesting attempts of the coastal California gnatcatcher (Grishaver et al 1998). Gnatcatchers typically live for two to three years, although ages of up to five years have been recorded for some banded birds (Braden et al. 1995). Most of the juvenile birds usually die during the cold winter months, although the percentage was not quantified. Observations indicate that gnatcatchers are highly vulnerable to extreme cold, wet weather (Mock et al., 1990).

Dispersal: Dispersal is a means by which genetic and demographic exchange between subpopulations maintains the viability of the regional metapopulation (Bailey and Mock 1998). Details regarding the dispersal effect on genetic and demographic connectivity of subpopulations and the actual requirements for dispersal are largely unknown (Rotenberry and Scott 1998) but some information can be documented from anecdotal observations. The mean dispersal distance of gnatcatchers banded as nestlings for males was 2.85 km and for females was 3.33 km (Atwood et al. 1996). Mean dispersal of juveniles in Orange County was found to be 1.05 km with one individual dispersing a total of 7.55 km (Galvin 1998). Although the mean dispersal distances that have been documented above are relatively low, dispersal of juveniles is difficult to observe and to document without extensive banding studies. It is likely that the few current studies underestimate the gnatcatcher's typical dispersal capacity because of the difficulty of detecting (Bailey and Mock 1998). Juvenile coastal California gnatcatchers are apparently able to traverse highly man-modified landscapes, including non-native landscaping vegetation, for at least short distances and this underestimation of the species' dispersal capability can lead to an overestimation of the metapopulation's vulnerability to extinction (Bailey and Mock 1998). A few observations of gnatcatcher dispersal behavior indicate that a stepping stone linkage, that is, a serious of small patches of suitable habitat interspersed with developed habitat, is deemed acceptable for situations where the habitat is otherwise fragmented and no contiguous linkage is available (Bailey and Mock, 1998). Additionally, natural and restored coastal sage scrub habitat along highway corridors has been documented to be used for foraging and nesting by gnatcatchers and may serve important dispersal functions (Famolaro and Newman 1998). Typically, however, the dispersal of juveniles requires a corridor of native vegetation which provides foraging and cover opportunities to link larger patches of appropriate sage scrub vegetation (Soule 1991). These dispersal corridors may facilitate the exchange of genetic material and provide a path for recolonization of areas from which the species has been extirpated and increased mating opportunities for unpaired birds (Soule 1991; Galvin 1998).

The natal dispersal, for a non-migratory bird, such as the coastal California gnatcatcher, is an important aspect of the biology of the species (Galvin 1998).

Socio-Spatial Behavior: The coastal California gnatcatcher seems to become highly territorial by late February or early March each year. Males seem to be very vocal during this time period (Mock et al., 1990). In San Diego County the territory size for inland sites was calculated to range between 13 and 39 acres per pair, averaging 24 acres per pair (ERCE 1990). In Riverside County, it was estimated that about 24 acres of sage scrub habitat (3 times the average territory size of 8 acres as measured within the HCP area) was required per pair of coastal California gnatcatchers (Braden 1998, pers. comm.). The distribution of the gnatcatcher is thought to be related to elevation with most of the birds located below 250 m elevation within 35 km of the coast and 500m elevation for inland regions (Atwood and Bolsinger 1992). During the nonbreeding season, gnatcatchers have been observed to wander in adjacent territories and unoccupied habitat increasing their home range size to approximately 78 percent larger than their breeding territory (Preston et al. 1998). Estimates of the territory size should be examined with caution as the calculation may be influenced by differences in data collection and analysis (Atwood et al. 1998).

Coastal California gnatcatchers are most often observed in pairs even in the non-breeding season. They appear to maintain their territories and are relatively sedentary throughout the year (Dunn and Garrett 1987). In fact vocalization rates, which may provide communication within the pair, were highest from August through March (Preston et al. 1998).

Community Relationships: Predation occurs in greater proportion in the upper and lower one third of the nest shrub. Predation was lower in nests with full clutch sizes which may indicate the parents are more attentive to the nest after the clutch is complete (Sockman 1997). Potential predators include scrub jays, greater roadrunners, and cactus wrens which have been observed to be actively mobbed by the gnatcatcher (Bontrager 1991). The coastal California gnatcatcher also is known to be affected by nest parasitism of the brown-headed cowbird. However, the gains in nest success from decreased nest parasitism appear to be negated by increased nest abandonment due to predation before cowbirds have migrated into an area (Braden et al. 1997). Thus, although a cowbird trapping program may reduce parasitism significantly and lower abandonment due to parasitism, nest predation then increases and negates the benefit of the trapping program (Braden et al. 1997). Nest parasitism apparently has resulted in earlier nesting dates of the gnatcatcher which may help compensate for the negative affect of parasitism (Patten and Campbell 1998).

Although the coastal California gnatcatcher may serve as an adequate "umbrella species" for other species that occur in similar habitats and that require a similar territory size or smaller (Fleury et al. 1998), it is not a particularly good indicator of bird-species richness in coastal sage scrub habitat (Chase et al. 1998).

Threats to Species

In 1997, the total number of gnatcatchers in the United States was estimated at 2,899 pairs, after subtracting out all gnatcatcher pairs authorized for Take under Habitat Loss Permits, approved natural Community Conservation Plans, Habitat Conservation Plans, and section 7 consultations ("Reinitiation of formal consultation on implementation of the special rule for the coastal Coastal California gnatcatcher [1-6-93-FW-37R1]"). This apparent increase in abundance since 1993 is likely the result of additional surveys occurring within previously unsurveyed areas, as well as increased productivity in response to favorable climatic conditions (USFWS 2000).

Although observed declines in numbers and distribution of the gnatcatcher resulted from numerous factors, habitat destruction, fragmentation and adverse modification are the principal reasons for the gnatcatcher's current threatened status (USFWS 1993). The amount of coastal sage scrub available to gnatcatchers has continued to decrease during the period after the listing of the species. It is estimated that up to 90 percent of coastal sage scrub vegetation has been lost as a result of development and land conversion (Westman 1981a, 1981b; Barbour and Major 1977), and coastal sage scrub is considered to be one of the most depleted habitat types in the United States (Kirkpatrick and Hutchinson 1977; Axelrod 1978; Klopatek et al. 1979, Westman 1987; O'Leary 1990). The fragmentation of habitat may artificially increase populations in adjacent preserved habitat; however, these population surpluses may be lost in subsequent years due to crowding and lack of resources (Scott 1993). In addition, agricultural use, such as grazing and field crops, urbanization, air pollution, increases in fire frequency and the introduction of exotics have all had an adverse impact on extant sage scrub habitat. A consequence of urbanization that is contributing to the loss, degradation, and fragmentation of coastal sage scrub is an increase in wildfires due to anthropogenic ignitions (human caused fires). High fire frequencies and the lag period associated with recovery of the vegetation may significantly reduce the viability of affected subpopulations of the gnatcatcher (USFWS 1991).

Special Biological Considerations

Knowledge of the demography of a population is fundamental to determining long-term trends. For birds, the demographic parameters of primary importance are annual breeding success, defined as number of chicks fledged per pair, and recruitment, defined as percentage of fledglings that enter the breeding population. A preliminary demographic model for a population of coastal California gnatcatchers based on observed data was prepared by Woehler et al (1995). Based on the results, for the population to be stable, each breeding pair must replace themselves over their lifetime. The data from a population at U.C. Irvine had a 90 percent mortality (that is, a 10 percent recruitment) and produced 0.64 fledglings per egg. In western Riverside County, 78.9 percent of the nesting attempts failed which translates to an approximately 80 percent mortality (Braden 1999). Thus, for the U.C Irvine example, a pair must produce 30 eggs during their lifetime and must live for five years for the population to remain stable (Woehler et al. 1995).

Gnatcatcher populations appear to be inversely correlated to seasonal total rainfall (Erickson and Miner 1998). Thus increased rainfall during the winter is a mixed blessing in that it is likely that it increases winter mortality but may increase the productivity of the invertebrate prey population base (Erickson and Miner 1998). Other weather-related factors that may influence the distribution of the gnatcatcher include the January mean minimum temperature which, for the coastal California gnatcatcher, has been estimated to be approximately 2.5 degrees C (Mock 1998). This metabolic constraint may preclude gnatcatchers, as a sedentary bird, from occupying otherwise suitable habitat within their range (Mock 1998). This link between a species distribution and physiological adaptations to the climate has been shown previously for other bird species (Hayworth and Weathers 1984).

Gnatcatchers nested earlier, had more successful nests, produced more fledglings, had a longer nesting period, and had lower fledgling costs when their territories were associated with increased grass and forb cover, increased perennial structure, increased horizontal perennial homogeneity, decreased vertical perennial homogeneity, and decreased perennial diversity (Braden et al. 1997). Thus, assessment of habitat quality should take into account these variables for preserve planning.

A habitat-based metapopulation model developed for the coastal California gnatcatcher revealed that the model predicted a fast decline and high risk of population extinction with most combinations of population parameters. The results were most sensitive to density-dependent effects, the probability of weather-related catastrophes, adult survival, and adult fecundity (Akcakaya and Atwood 1997). However, this metapopulation model resulted in the greatest difference on a time horizon of only a few decades. This may be appropriate if the model is used to compare alternative management options but not to make assessments with longer time horizons (Akcakaya and Atwood 1997). Studies providing information on long-scale demography and metapopulation variables are still largely unknown (Rotenberry and Scott 1998).

Structure of the perennial vegetation within coastal sage scrub seems to be an important component leading to successful gnatcatcher reproduction (Braden, 1997). Any disturbance that affects perennial structure and homogeneity within gnatcatcher territories, such as fire or grazing, also may affect gnatcatcher fitness (Braden, 1997). In fact, areas of the Southwestern Multiple Species Reserve that were occupied by gnatcatchers previous to a 1993 fire have not recovered enough to warrant occupation by gnatcatchers to date (Shaughnessy 1999 pers. comm.). In general, recently burned areas are not used by gnatcatchers except on an occasional basis, and five to seven years of recovery may be necessary before gnatcatchers will nest in burned areas (Atwood et al. 1998, Beyers et al. 1994). This slow recovery of CSS in western Riverside county may be due to invasion of exotic annuals after any disturbance. CSS in the County has been reduced by frequent fire, grazing, and invasion of exotic annuals, as well as air pollution (O'Leary and Westman 1988; O'Leary (1990). The frequency of fires in wildland areas tends to increase as fragmentation increases due to urbanization and agricultural activity. Because of the CSS to grass conversion, protection of coastal sage scrub on gabbro basalts may be required to protect this habitat and the gnatcatcher in Riverside County (Minnich and Dezzani 1998).

Fire may be an important factor to consider in MSHCP Conservation Area design for this species and management plans may be necessary to provide a strategic framework for merging the needs for the species with the challenges of fire control (Mackey et al. 1994). Consideration of habitat refugia, burn frequency, and recolonization of recovering burn areas will be necessary for designing reserves for this species (Atwood, et al. 1998). Observations after a major fire of coastal sage scrub reveal that a large proportion of the gnatcatchers within the burned area were displaced to adjacent habitat rather than killed outright and were packed more densely into remaining areas of intact coastal sage scrub (Atwood, et al. 1998). On unburned areas within San Diego and Riverside counties, two pairs per hectare were found, but only 0.02 pair per hectare were found on burned areas (Mayer and Wirtz 1995). However, the gnatcatchers that are able to establish territories on burned areas appear to breed at rates very similar to those on unburned sites (Wirtz and Mayer 1995). The extent and timing of vegetation recovery may determine the habitat suitability for breeding pairs (Wirtz and Mayer 1995).

The presence of gnatcatchers within burned areas may indicate post-fire dispersal or the availability of refugia from the fire (Mayer and Wirtz 1995). Frequent burning of coastal sage scrub may lead to domination of the site by introduced grasses, in addition, burned sage scrub often remains unsuitable for breeding gnatcatchers for more than eight years after burning (ERCE 1991, Zedler et al. 1983, O'Leary 1990). At an inland site, burned 12 years earlier, there was less than 10 percent shrub cover and no gnatcatchers, while annual grasses and mustard species dominated the site (Beyers et al. 1994). Management consideration will need to take into account that large scale fires may damage gnatcatcher populations in both the burned area and the refugia area (Atwood et al. 1998). Due to the issue of periodic fires in occupied habitat and the length of time needed for recovery of CSS, large areas will be necessary to provide refugia for birds and to supply dispersing individuals to a recovered area. As an example within the western Riverside County Plan Area, the Alberhill population is separated from other core populations by an existing firebreak in the form of the I-15 freeway corridor. Thus, if a wildfire occurs east or west of I-15, the population on the opposite side of the freeway will likely be protected. Duplicate linkages also provide for the temporary loss of function of the coastal sage scrub habitat in the event of a fire (Campbell et al. 1998). A duplicity of habitat linkages composed of sage scrub and other undeveloped habitats which may be composed of native as well as non-native habitats may provide for dispersal ability of the species (Campbell et al. 1998).

Other factors that will be relevant for designing a reserve system for the gnatcatcher will be the dispersal distance and average territory size. In western Riverside County, the average dispersal distance for juvenile gnatcatchers has been documented as 1.14 km (Braden et al., 1994a). The distances may be influenced by many factors such as sex, reproductive opportunities, available habitat and other factors. The average territory size for gnatcatchers is 8.42 acres during the breeding season and can expand to 60 acres during the non-breeding season (Braden and Powell, 1994b). Other studies have concluded the territory ranges in size depending on the location and a study in Riverside County concluded the average territory size is 8 acres (ERCE 1990, Braden 1998, pers. comm.). A reserve design for this species will need to maintain connections of breeding habitat such that dispersal between areas can be accomplished and that are large enough to accommodate the largest territory sizes.

Linkages of habitat along linear features such as highways and power-line corridors may be of significant value in linking populations of the gnatcatcher (Famolaro and Newman 1998). Stepping stone linkages which are designed to function as habitat linkages are acceptable but should be line of sight as much as possible (Bailey and Mock 1998). The width of a linkage is recommended to be approximately 1,200 feet. This will provide a linkage wide enough to support a gnatcatcher territory. For linkages less than this width, the gnatcatchers currently mapped for occurring within the linkage may not be able to remain within the area. In the case of narrow habitat widths, the linkage will serve the function of connection of habitat areas only. An important linkage of habitat to maintain or encourage is that from the western Riverside County area north into San Bernardino County (Davis et al. 1998). This linkage is within the Jurupa Hills and connects to the Santa Ana River in Riverside County (Davis et al. 1998). Recently, gnatcatchers have been observed within Jurupa Hills although the area is not surveyed regularly (Davis et al. 1998).

The coastal California gnatcatcher may be suitably analyzed on a landscape or habitat basis rather than on a data point basis due to the fact that it responds well to habitat management and will readily occupy revegetated coastal sage scrub (O'Connell and Erickson 1998, Miner et al. 1998). The fact that gnatcatchers will occupy revegetated coastal sage scrub makes this an important component of long-term management for the species (O'Connell and Erickson 1998). In one study, restored habitat was included in 19 of 22 gnatcatcher territories and nests in restored areas were as likely to produce at least one young as nests in naturally generated scrub (Miner et al. 1998). Additionally, in this study, thirteen percent of the nests were placed within 3 meters of actively used roads or trails and their success rate was similar to that of nests placed further from these high-use areas, thus breeding success of gnatcatchers appears not to be negatively affected by current management practices and levels of public use within park areas. (Miner et al. 1998). Given that this study was conducted within specific State Park areas, additional studies would be helpful for other situations.

The continued fragmentation of habitat over time has increased exposure of gnatcatcher to threats associated with habitat edge (Atwood 1993). Numerous nest predators thrive on habitat edges, and brood parasitism by the brown-headed cowbird (Molothrus ater) appears to be exacerbated by increased edge effects (Bolger et al. 1997, Atwood 1993). Management of edge effects of future development may also be needed although there is little evidence that coastal California gnatcatchers are negatively affected by having their territory located at the edge of urban development (Atwood, 1998). This may be more associated with the use of the gnatcatcher of sage scrub/grassland ecotone. In support of this observation, studies of ‟edge/fragmentation reduced" species versus ‟edge/ fragmentation enhanced" species places the coastal California gnatcatcher in an ‟edge/fragmentation insensitive" category (Bolger et al. 1997). This is a category occupied by the characteristic species of shrub habitats in the region. They tend to be abundant and widely distributed across the landscape and habitat gradients although their abundance is much lower than the other species in the group (Bolger et al. 1997). Other forms of edge management may still be required. Management may include fencing areas occupied by gnatcatchers to protect birds from human and other intruders. Management may include exotic plant removal along edges of development or planting with native shrubs. Analysis of the current shrub cover to shrub cover and composition in 1934 indicates a drastic reduction in native species and increase in non-native grasses and forbs (Minnich and Dezzani 1998). A major portion of the degradation in the Perris plain of Riverside County is within public land with private lands nearby containing higher quality habitat. Attempts to conserve the coastal California gnatcatcher by extending public lands in regions experiencing this habitat degradation may be insufficient (Minnich and Dezzani 1998).

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