Bull. SouthernCaliforniaAcad. Sci. 114(1),2015,pp.42-53 ©SouthernCaliforniaAcademyofSciences,2015 Recent Decline ofLowland Populations of the Western Gray Squirrel in the Los Angeles Area of Southern California Daniel S. Cooper1 and Alan E. Muchlinski2 1Cooper Ecological Monitoring, Inc., 255 Satinwood Ave., Oak Park, CA 91377 2Department ofBiological Sciences, California State University, Los Angeles, 5151 State University Drive, Los Angeles, CA 90032 — Abstract. We provide an overview of the distribution of lowland and otherwise isolated populations ofthe western gray squirrel Sciurusgriseus) in the Los Angeles ( area of southern California, an area that has experienced a recent and ongoing invasion by the non-native eastern fox squirrel Sciurus niger an urban-adapted (, ), species introduced a century ago. Away from its strongholds in the western Santa Monica Mountains, San Gabriel Mountains, and Santa Ana Mountains, the western gray squirrel is resident locally in both the Santa Susana and the Verdugo Mountains, in Griffith Park, in low hills at the eastern periphery ofthe San Gabriel Valley and in Claremont, and along the Santa Ana River canyon near Yorba Linda. It also persists east of the Los Angeles area in residential areas of Redlands and Yucaipa, which as of2014 are still outside the range ofthe eastern fox squirrel. Here we document several gray squirrel extirpation events within its lowland range, and discuss factors influencing its persistence and its extirpation. The western gray squirrel (Sciurus griseus) is a large tree squirrel native to forests of the western United States and extreme northwestern Mexico, with the subspecies S. g. anthonyicommon and widespread in oak- and pine-dominated areas ofthe hills and mountains of southern California (Wilson and Reeder 2005). In the Los Angeles area, a region we define as extending from eastern Ventura County east through Claremont and south through the coastal plain into Orange County to the base ofthe San Joaquin Hills, it also occurs in human-modified habitats, including large city parks and golf courses, where scattered trees, particularly conifers, provide year-round food and shelter. It is one of two tree squirrels in the Los Angeles area, the other being the eastern fox squirrel {Sciurus niger), a non-native introduced in the early 1900s, and now abundant throughout much ofthe Los Angeles area of southern California (Jameson and Peeters 1988, King et al. 2010). As discussed by Linders and Stinson (2007) western gray squirrels are closely tied to oak and evergreen woodland, and serve two main roles in maintaining nativewoodlands: they harvest and bury acorns throughout the woodland, and disperse the seeds and fruit of various oak woodland component tree and shrub species, such as California bay {Umbellaria californica). They also forage heavily on truffle-like mycorrhizal fungi found in leaflitter and loose soil, which aid oaks in fixing nitrogen and retaining water through dry months. During foraging, western gray squirrels deposit the spores of these fungi through their droppings, thus spreading them throughout the oak woodland and promoting the health ofits trees. Because ofthis close association with oaks, the presence Corresponding author: [email protected] 42 WESTERN GRAY SQUIRREL IN LOS ANGELES AREA 43 ofwestern gray squirrels may serve as an indicator ofoak woodland health. By contrast, the eastern fox squirrel is highly generalist in its food sources, requires a much smaller home range (becoming super-abundant in urban settings), and occurs in a much wider array of habitats than S. griseus away from the major mountain ranges in the region (Gatza 2011, Ortiz 2014). The history and origin of western gray squirrel populations on the floor of the Los Angeles Basin are poorly understood. Today, most lowland populations ofS. griseus are strongly associated with planted pines and other conifers, which may now be crucial habitat elements for the species. It was presumably naturally present at lower elevations when oak woodland (mostly Quercus agrifolia once covered large areas of now- ) urbanized places like the San Gabriel Valley, a pattern shared by numerous lower montane plant and wildlife species that are able to persist locally at lower elevations in suitable areas ofcanyons and woodlands (Cooper 2011). Later, as the region developed, populations of S. griseus may have retreated to large urban parks and more wooded residential areas, where itpersisted throughmost ofthe 1900s, includingthose at thebase of the San Gabriel Mountains foothills from Pasadena east into Claremont (an area referred to as the “mesa” by early naturalists, e.g., Grinnell 1898). It is also possible that they colonized these areas later by moving down from the surrounding foothills, or that both patterns occurred, with isolated lowland populations “winking” out periodically, replenished by animals from surrounding highlands. Whatever the history, in the years between the late 1990s and the mid-2000s, S. griseus became scarce or altogether absent within many of these same neighborhoods. Clear instances of its extirpation and subsequent replacement - directly or indirectly - by the non-native eastern fox squirrel are now well documented (e.g., Muchlinski et al. 2009, Guthrie 2009, King et al. 2010). Sciurus niger became established in the neighborhoods surrounding the eastern Santa Monica Mountains in the western Los Angeles Basin during the decades following its introduction in 1904, it only arrived in the San Gabriel Valley around 1990, the east San Gabriel Valley around 1998, and the Claremont area and Orange County in the early 2000s (Guthrie 2009, King et al. 2010). In recent years, S. niger has also colonized much ofurbanized Santa Barbara County (P. Collins, pers. comm.) and portions ofSan Diego County, the latter also following an early introduction (King et al. 2010). Now virtually ubiquitous throughout the Los Angeles area from the San Fernando Valley east to San Bernardino County and south through Orange County, S. nigerappears to still be absent at several urban-edge locations at the margins ofthe Los Angeles area, including parks and neighborhoods in Redlands and Yucaipa, San Bernardino Co. (Ortiz 2014); canyons in thelower San Gabriel Mountainfoothills fromthe Sunland-Tujungaareaeast through Claremont(Gatza 2011), and along the SantaAna Riverat GypsumCanyon, nearYorba Linda, Orange Co. (AEM, unpubl. data). Only a handful oflocal naturalists have noticed this turnover, and few published data exist on the range ofS. griseus in the Los Angeles area prior to the arrival of S. niger. Today, only a few populations of S. griseus remain away from the larger mountains m [typically below around 457 (1500’) a.s.l.], with only a handful, at the far eastern periphery being free of S. niger. To ensure the ecological integrity of these remaining populations of S. griseus - and of their habitat patches - particularly in areas where S. niger has not yet invaded (or at least where it is not completely dominant), it is important that remaining populations of S. griseus be identified and recognized by conservation agencies and organizations. Since the late 1990s, we (DSC and AEM) have been making notes on the occurrence ofS. griseus in the Los Angeles area, as described 44 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 0 5 10 20mi. k Distribution ofwestern graysquirrel (Sciurusgriseus) 1—I—I —I —I I—I—I —I — ^ JpF] CoreWGSpopulations Freeways/majorhighways 0| I 1I0 I 2|0 I I I 4|0kmIn /s/ # Persisting DRealtiaefSCoouprycreigChrte:di©ts:2B01a4seEmSRaIp,-WeWsotrelrdnSghraadyed Irregular/Unknown Counties squirreldistributiondatabyDanielS.Cooper O Extirpated <? andAlanMuchlinski,mapdesignbyJennifer Mongolo,November2014. Fig. 1. Map showing current (2012-2014) range ofwestern gray squirrel in the Los Angeles area. below. This paper synthesizes findings from each ofthese efforts and provides detail on a dramatic and ongoing ecological replacement ofa native species by a non-native one. Materials and Methods Little published information exists on the current or historical distribution of the western gray squirrel, so we relied on a variety of sources, including online museum databases for specimen records (www.vertnet.org, last search conducted 21 October 2014), and field notes and recollections ofa network ofenvironmental professionals and colleagues in the Los Angeles area. DSC conducted surveys ofbirds and vegetation in the Puente and Chino Hills on the east side ofthe Los Angeles Basin for two years in the late 1990s (1997-1998; see Cooper 2000), and kept field notes of all sightings of S. griseus AEM from this area. collected data on observations of S. griseus through an online survey form (http://instructionall.calstatela.edu/amuchli/squirrelform2.htm), which has received over 9000 visits since January 23, 2007, through field studies by four graduate students (Lewis 2009, Gatza 2011, Erkabaeva 2013, Ortiz 2014), and through his own observations within and east ofthe San Gabriel Valley. DSC initiated a volunteer-based tree squirrel survey ofGriffith Park in summer 2010; with ten observers each searching up to five of 40 similarly sized survey blocks in and WESTERN GRAY SQUIRREL IN LOS ANGELES AREA 45 around the park. The following year, DSC and volunteers spent 25 days in the park between 8 August and 21 November 2011, gathering observations on foraging, breeding, aggression displays and other behavior, and from 5 August 2011 to 11 July 2012, DSC conducted a region-wide search for any remaining S. griseus populations in the lowland Los Angeles area away from known occupied habitat. During this period, DSC posted short articles and requests for information on local listserves (e.g., Pasadena Audubon Society; various neighborhood “Patch” websites). Also, DSC and colleagues made site visits (30 min - 2.5 hrs in duration) on 21 dates to 32 different locations in the eastern Santa Monica Mountains, the west San Gabriel Valley, and in the Verdugo Mountains and San Rafael Hills north of Glendale following up on reports and checking all accessible lowland areaswithappropriatehabitat. To supplementthese surveys, DSCand colleagues installed motion-activated cameras during the same time period at Descanso Gardens in the San Rafael Hills west of Pasadena (two near the upper portion of the property bordering open space) and in the Verdugo Mountains (nine within canyons in three areas: La Tuna Canyon, Cedarbend Canyon, and Whiting Woods; ibid). Results Within its core range in mountains at the periphery of the Los Angeles area, Sciurus griseus is a conspicuous resident in canyons and oak groves, and appears to have little contactwith S. nigerexcept attheimmediateurban-wildlandinterfacezone (Gatza2011). m Below around 457 (1500’) a.s.l., numerous subpopulations ofS. griseus persisted into the 1990s in areas between these majormountain ranges, and in somecases, well onto the floor ofurbanized areas, as summarized below, and in Figure 1 and Table 1. Eastern Santa Monica Mountains!Griffith Park Griffith Park, at the far eastern end of the Santa Monica Mountains, appears to support the onlylarge remainingpopulation ofthe species in this range east ofSepulveda Pass/Interstate 405, with approximately 25-50 individuals largely confined to two main drainages (Western Canyon and Vermont Canyon). During intensive searches of potential habitat in 2011 and 2012, no observations of S. griseus were made between Sepulveda Pass and Cahuenga Pass (U.S. 101), an area that includes significant open space at Franklin Canyon Park and elsewhere. However, we remain hopeful that S. griseus may persist here, as we were unable to obtain access into the large Stone Canyon Reservoir open space (Los Angeles Dept, of Water and Power) just east of Sepulveda Pass near Bel Air, which supports apparently suitable habitat. Santa Susana Mountains!Simi Hills Located on the northwestern edge of the San Fernando Valley, these generally arid ranges are dominated by low-growing chaparral and coastal sage scrub, with a small number ofpermanent streams and oak woodlands, best developed in the former range. Ecologically, the Simi Hills aremore similarto the Santa Monica Mountainsimmediately to the south than the San Gabriel and Sierra Madre ranges to the north, while the Santa Susana Mountains reach higher elevations and feature more montane elements such as bigcone douglas-fir Pseudotsugamenziesii) andextensive savannah dominated by annual ( grassland and valley oaks (Quercus lobata). Based on field notes of local naturalists, S. griseus is absent from the Simi Hills, but persists in the Santa Susana Mountains at Browns Canyon and Devils Canyon (S. Bernal, 2012, in litt.), and possibly at O’Melveny Park (sight record on 20 April 2014, CSULA web survey). Its historical status in either 46 SOUTHERN CALIFORNIAACADEMY OF SCIENCES Table1. Distributionof“lowland”populationsofwesterngraysquirrelinLosAngelesarea(i.e.,away frommajormountainranges/foothills), 2014. Status: P = Persistingpopulation; E = Extirpated; EFS = Easternfoxsquirrel. Location, Date oflast Region Subarea as applicable Elevation Status EFS? record (Source) East Santa Monica Mountains Beverly Hills <1200’ E Yes 1975 (specimen, LACM 60617) Griffith Park <1200’ P Yes 2014 Santa Susana Mountains 1400’ P Yes 20141’2 West San Gabriel Valley Verdugo Mountains 1800’ P Yes 2012 (DSC, unpubl. data) San Rafael Hills 1300’ P Yes 2014 (Erkabaeva 2013) San Marino Huntington 600’ E Yes 2010 (CSULA database) Library Lacy Park 600’ E Yes 1976 (specimen, LACM90234) Mission Canyon3 600’ E Yes 2012 (CSULA database)4 Northeast Los Angeles (Forest Lawn Glendale) 600’ E Yes 1997 (DSC, unpubl. data) East San Gabriel Valley San Jose Hills Industry Hills 600’ P Yes 2014 (AEM, unpubl. data) Bonelli Park area5 1000’ P Yes 2014 (AEM, unpubl. data) WalnutCreekPark 800’ E Yes 2012(DSC,AEM,unpubl.data) Galster Park 600’ E Yes 1998 (DSC, unpubl. data) Cal Poly Pomona 800’ E Yes 2009 (AEM 2009) Via Verde Country 800’ E Yes —2000 (AEM, unpubl. data) Club Western Puente Hills6 Whittier/Hacienda 800’ E Yes 1998 (DSC, unpubl. data) Heights Powder Canyon 800’ E Yes 2005 (R. Erickson, unpubl. data) Eastern Puente Hills/Chino Hills Tonner Canyon 600-800’ P Yes 2014(R. Hamilton, L. Schmahl, viaemail) Chino Hills State 1200’ P Yes 2014 (A. Ing, pers. comm.) Park Pomona Valley/Claremont RSABG7 1200’ P Yes 2014 (AEM, unpubl. data) Pomona College 1200’ E Yes 2012 (AEM, unpubl. data) Arlington Dr. 1200’ P Yes 2012 (CSULA database) Redlands/Yucaipa North ofI-10 Univ. ofRedlands/ 1500’ P No 2014 (Ortiz 2014) Sylvan Park 3rd St., Yucaipa 2600’ ? No 2011 (CSULA database) South ofI-10 Ford Park 1600’ P No 2014 (Ortiz 2014) Prospect Park 1600’ P No 2014 (Ortiz 2014) Rossmont Dr. 2000’ ? No 2009 (CSULA database) Hilltop Dr. 2200’ P No 2012 (CSULA database) WESTERN GRAY SQUIRREL IN LOS ANGELES AREA 47 Table 1. Continued. Location, Date oflast Region Subarea as applicable Elevation Status EFS? record (Source) Orange County Anaheim Hills OakCanyonNature 800’ P Yes 2013 (CSULA database) Center Santa Ana River Canyon Yorba Reg. Park 400’ P Yes 2014(B.Leatherman,viaemail) Canyon RV Park 400’ P No 2014 (AEM, unpubl. data) 1Includes sight record from O’Melveny Canyon Park in 2014 (CSULAweb survey). 2S. Bernal, unpubl. data. 3IncludesoakwoodlandpatchesalongKewen,CanonandEncinoDr.atSanMarino/Pasadenaborder. 4Thispopulationwasseencontinuouslythrough2010;the2012reportwaslikelyadispersingindividual from elsewhere. 5Includes Mountain Meadows GolfCourse. 6We use State Route 57 as the east/west dividing line. 7Rancho Santa Ana Botanic Garden, Claremont. range is not known (a single specimen exists from “Oat Mountain” from 1969, LACM A 47332), nor is the size ofthe extant population in the Santa Susana Mountains. recent (2014) observation of a roadkill S. griseus on U.S. 101 at Las Virgenes Canyon Rd. (C. DeMarco, via email) suggests that colonization north from the Santa Monica Mountains might be a possibility without the freeway and associated development as a barrier. Sciurus niger is common in the Simi Hills, particularly at the urban periphery (DSC, pers. obs.). Verdugo Mountains!San Rafael Hills Populations ofS. griseus in both the Verdugo Mountains and the adjacent San Rafael Hills are isolated from the San Gabriel Mountains to the north by Interstate 210 and by dense residential development along Foothill Blvd. Despite searching promising areas such as La Tuna Canyon Rd., Crescenta Valley Park and the Whiting Woods neighborhood on the north slope of the Verdugos, and Descanso Gardens and Scholl Canyon in the San Rafaels, we could not locate any individuals during observational surveys in 2011-12. However, in approximately three months operatingmotion-activated cameras in 2012, we detected single individual S. griseus at two sites, one in Cedarbend Canyon and onenearWhitingWoods, confirmingthat the speciespersistsintheVerdugo Mountains. In the San Rafael Hills, Erkabaeva (2013) observed four S. griseusin a group on one occasion at Descanso Gardens in La Canada, as well as several lone individuals here during 2012. Later, a motion-activated camera that had been placed at Descanso Gardens since 2012 recorded a single S. griseus in July 2014, indicating the persistence of at least a small population here. Sciurus niger is very common throughout both the Verdugo Mountains and San Rafael Hills, includingwithin seemingly pristine habitat far from development (DSC, pers. obs.). Northeastern Los Angeles The hilly residential neighborhoods ofLos Angelesjust south ofthe San Rafael Hills (including Eagle Rock and Highland Park) appear to have also lost at least one lowland population ofwestern gray squirrels. Several individuals were observed in planted pines in the upper portions ofForest Lawn Glendale on the Eagle Rock border in 1997 (DSC, 48 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES pers. obs.), but a check in 2011 (this study) revealed only S. niger. Lack ofrecords from considerable time afield in this region and no sightings by naturalists based at the Debs Park Audubon Center in Highland Park (J. Chapman, pers. comm.) suggest that no current population of S. griseus persists in this area, which includes the lowermost portion of the Arroyo Seco. PasadenalWest San Gabriel Valley Small numbers of western gray squirrel occur at the northern/urbanized edge of Pasadena/Altadena (c. 457 m a.s.l.), where S. nigerisnow abundant. Onewas observedin 2011 (DSC) in the courtyard of an abandoned U.S. Forest Service facility adjacent to HahamongnaWatershed Park nearthe Pasadena/La Canada border, and accordingto a local resident, up to four individuals, including a probable family group (in January 2011), have been recorded here in recent years (L. Paul, via email). Sciurus griseus is occasional in the more wooded residential neighborhoods along the northern tier of Altadena at the base ofthe mountains (e.g., near Eaton Canyon and Kinneloa Canyon), but has apparently abandoned locales slightly downslope in denser residential areas, including a former retirement facility (“The Scripps Home” at 2212 N. El Molino Ave.) that had its mature trees removed prior to a redevelopment effort in summer 2011 (an action which apparently drove out S. griseus fide L. Paul). More significantly, , a population of S. griseus that once occurred in remnant oak-walnut woodland amid residential estates along Mission Canyon at the border of San Marino and Pasadena (including Lacy Park) persisted to around 2012, with the last records (each of a single individual) being along Kewen Drive in San Marino on several dates in 2010 (J. Garrett, via email), and again in 2012 (M. Nakamura, CSULA web survey form). We also last received reports from the nearby Huntington Library around the same time (three separate sightings; T. Allison, CSULA web survey forms in 2008 and 2010; S. Claytor, photograph in 2008). We knowofno remainingpopulation ofS. griseushere oralongthe lower Arroyo Seco south of Hahamongna/Devil’s Gate Dam. East San Gabriel Valley!San Jose Hills As in the west San Gabriel Valley, western gray squirrels occur widely in canyons and locally in residential areas in the foothills on the northern tier of the east San Gabriel m Valley(e.g., above Monrovia, San Dimas and LaVerne, >305 a.s.l.). Southofhere, the low range of hills in the eastern San Gabriel Valley referred to as the San Jose Hills apparentlyservesasanecologicalconnectionbetweenthe SanGabriel Mountainsandthe Puente-Chino Hills, which then connect to the much larger Santa Ana Mountains to the south(seeCooper2000). Here, thespeciespersistsonlyatBonelliPark(SanDimas)andin the “Industry Hills” near La Puente, and several extirpations have been very recent (e.g., observedbyDSC atWalnut CreekParkin Covinain2011 butnotsinee;fideAEM). Puente-Chino Hills Western gray squirrels occurred in multiple canyons and open space areas from Diamond Barand Rowland Heights west into Whittierand La Habra Heights, and south into Brea, and Chino Hills State Park during the late 1990s (DSC, unpubl. data). A population in Turnbull Canyon in the Whittier Hills (far western Puente Hills) was apparently extirpated in the late 1960s following a major fire that burned many mature oaks (J. Schmidt, in litt.), indicating that even by then some loss had occurred. By thelate 2000s they had been extirpated west of Harbor Blvd., with replacement by S. niger, WESTERN GRAY SQUIRREL IN LOS ANGELES AREA 49 including along Powder Canyon in Rowland Heights/La Habra Heights, where S. griseus was present in late 2005 (1, R. Erickson, unpubl. data) yet absent by 2007 (DSC, unpubl. data; fide L. Longacre). The latter location is particularly notable, as the canyon is directly contiguous to hundreds ofacres ofnatural habitat, has been protected as part of the Puente Hills Landfill Conservation Authority, and has seen little if any land use change in the past 20 years. A devastating fire in 2008 that burned most ofChino Hills State Park resulted in the immediate loss ofmostwestern gray squirrelpopulations there, with only a very small number ofindividuals persisting in oak woodland in the remote center ofthe park, north of San Juan Hill (A. Ing, pers. comm.). Pomona Valley!Claremont While still present at Rancho Santa Ana Botanic Gardens and along the San Gabriel foothills through the northern portion ofClaremont (e.g., San Dimas Canyon, Marshall Canyon, fide AEM), western gray squirrel has been recently extirpated from several areas, and replaced by S. niger, within the city ofClaremont to the south, including the Claremont Colleges area (Guthrie 2009). There are apparently no historical or recent records of S. griseus from the eastern Pomona Valley nor along the lower Santa Ana River Valley upstream ofPrado Dam. Redlands!Yucaipa (San Bernardino County) Western gray squirrels are widespread and conspicuous residents of the San Bernardino Mountains. However, lowland populations away from the lower foothills persist (as of2014) at UniversityofRedlands, SylvanPark, FordPark, andProspect Park (Ortiz 2014). The species has also been reported in the “Sunset Hills” area of Redlands just south ofInterstate 10 and in an apparently small area ofYucaipa (including Third St.), where they are found in mature pines in a residential area (CSULA web survey). These populations do not appear to be in contact with S. niger as of2014, and are much higher in elevation than other lowland sites discussed. However, because they are persisting away from the main mountain ranges in what is still obviously lowland (non-montane or foothill) habitat, we have included them here. South Orange County In contrast to the report by Pequegnat (1951) that the western gray squirrel was not found in the Santa Ana Mountains, the species is present in several oak-filled canyons in the Santa Ana Mountains (e.g., Trabuco Canyon, CSULA web survey and J. Ortiz, via email; Modjeska Canyon/Tucker Wildlife Sanctuary, CSULA web survey; Whiting Ranch Wilderness Park, R. Hamilton, via email). Additional reports to the CSULA web survey locate western gray squirrels at the suburban-wildlands interface west of Lake Elsinore. Whether they are recent (post-1950s) arrivals to this range is not known. Away from the Santa Ana Mountains, two small populations are known from Oak Canyon Nature Center in the Anaheim Hills, and along the “Santa Ana River canyon” where the Chino Hills meet the northern Santa Ana Mountains (AEM, unpubl. data; B. Leatherman, via email). We know of no records from the San Joaquin Hills, where S. niger has been present in residential areas since around 2010 (R. Erickson, via email). Like much of San Bernardino (and Riverside) County, S. niger has only recently (late 1990s) penetrated Orange Co., but it is now widespread and common into Irvine (D. Willick, via email). 50 SOUTHERN CALIFORNIAACADEMY OF SCIENCES Other Areas DSC (unpubl. data) observed a small number of what appeared to be western gray squirrels in pines at the golfcourse at the Palos Verdes Country Club near Malaga Cove on the Palos Verdes Peninsula in the 1990s; in this same area in roughly the same time period, a local naturalist observed what appeared to be a single individual in the same A area (R. Melin, via email). recent visit to this area (October 2014) revealed that it still supported a dense forest ofcoast live oak, toyon (Heteromeles arbutifolia), many mature planted conifers and eucalyptus, and a riparian strip running through the golf course (DSC, pers. obs.). And, whereas the eucalyptus plantation here has apparently been established formore than a century(Gales 1988), due to the extreme isolation ofthis area from any other known S. griseuspopulations, its coastal location, and the possibility that this population derived from deliberately introduced individuals (or pertains to the eastern gray squirrel, Sciurus carolinensis), we consider a Palos Verdes population to be "hypothetical” for now until more information is uncovered that would support its inclusion in the current range of the species. Discussion Our investigation into the distribution ofthe western gray squirrel in the Los Angeles area elucidates its status as essentially a foothill species that is now rare and declining m below around 457 elevation, particularly in areas where it has come into contact with the eastern fox squirrel. Away from its main strongholds in the western Santa Monica Mountains, the San Gabriel Mountains, and the Santa Ana Mountains, small, isolated populations persist only in the Santa Susana Mountains, Griffith Park, the Verdugo Mountains and San Rafael Hills, the San Jose Hills, the Chino Hills, at Rancho Santa Ana Botanic Gardens in Claremont, and in Redlands/Yucaipa. Based on local naturalists’ observations, several lowland populations appear to have declined in the past five years, including that in Bonelli Park, the San Rafael Hills, Chino Hills State Park, and along the Santa Ana River Canyon nearYorba Linda. Invariably, extirpations have occurred concurrently with colonization by the ubiquitous S. niger. It is probably unlikely that truly extirpated, isolated lowland populations in the area will re-develop on their own. Areas of recent extirpation (or near-extirpation, where S. griseusis no longerresident butmay occurirregularly) are typically separated fromthe nearest presumed source population by more than a kilometer, and generally by dense residential or urban development. Multi-lane freeways now provide formidable barriers between these areas of extirpation and source populations of S. griseus. Remarkably, animals do persist in a handful oflowland areas with very limited habitat, including the Industry Hills in La Puente, which suggests that certain small, isolated subpopulations may act as “refugia”, perhaps frompathogens that periodically sweep through largerand more intact populations. Of course, these same refugia are vulnerable to their own extinction events, and so are almost certainly temporary. Erkabaeva (2013) demonstrated that the length of projected coexistence of the two squirrel species in a given habitat fragment depends upon both the size of the habitat fragment and the structure ofthe habitat within the fragment, with length ofcoexistence associated with a higher diversity of food bearing tree species and coniferous trees. Sciurusgriseus had a high probability ofgoing extinct within a relatively short period of time (10 to 40 years) in small to medium-sized habitat fragments. The presence of the S. niger in the same habitat brought about extinction in a shorter period oftime. WESTERN GRAY SQUIRREL IN LOS ANGELES AREA 51 Competition with other squirrel species has been suggested as a potential cause of S. griseusdecline(oracontributorto itscurrent patchydistribution) inthe region, but the mechanisms involved in this relationship need further study. Extirpation sites generally support very highdensities ofS. niger yet this species simply occurs at higherdensities in , general. Sciurusniger is highly urban-adapted, and occurs at all the sites where S. griseus has vanished, and we have not confirmed a site where S. griseus has been extirpated and where S. niger is completely absent. Still, King (2004) found few interactions among S. niger, S. griseus, and even California ground squirrel (Spermophilus beecheyi) in her study area where all three occur in San Dimas, California (eastern Los Angeles Co.), and Ortiz (2014) also observedveryfewaggressiveinteractions between S. nigerand S. griseus inherlocal studyareas. Regardlessofthemechanism, thelossofS. griseusintheseareas- and region-wide-may be associated with a profound ecological change and degradation of seemingly healthy oak woodland and other habitat, particularly in wildland areas where replacement has occurred (e.g., the Puente-Chino Hills). Larger wildland areas where S. griseus is persisting in the presence of S. niger are of particular interest because these appear to offer the basic habitat needs ofboth species, at least for some period of time, and possibly in different areas of the landscape. The discovery ofnests ofS. griseus well into protected open space such as in the rugged Cedarbend/Whiting Woods area ofthe Verdugo Mountains (DSC, unpubl. data) and at San Dimas Canyon Park (King 2004) suggests a pattern of edge-avoidance, possibly relatedto increasedcompetition with theeastern fox squirrel at theurban edge. However, this pattern breaks down at sites like Fern Dell in Griffith Park, where S. griseus occurs a few feet from houses and dense urbanization (DSC, unpubl. data). Here, supplemental feeding or food provisioning may simply be “propping up” the population ofS. griseus which has also been aided by the abundance ofplanted trees providing additional food sources (fruits and nuts). Although we have made a few direct incidental observations of supplementalfeeding (e.g., unshelledpeanuts dropped at Fern Dell in Griffith Parkbeing carried offby S. griseus), it probably occurs widely. Other vegetative characteristics that allow S. griseus to persist here include some amount of closed-canopy woodland (orwoodland-like groves oftrees) with an open understory rich in non-woodydebris and leaflitter; older, mast-producing trees for food; and at least a few very tall trees for nest placement (Linders and Stinson2007), characteristics that still apply tomanyparksin the region. More proximate factors in the decline ofS. griseus relevant in our study area include death from injury and disease. Mortality from roadkill has been shown to be a major (iflocalized) factor in squirrel deaths in studies in Washington state (Linders and Stinson 2007), and S. griseusisfrequentlydetectedas roadkillinthe LosAngeles area (pers. obs.). Many sites at the urban-wildland interface, including sites with documented S. griseus extirpations haveroads alongacanyonbottom, makingsquirrels thatliveinlowdensities and that forage on the ground particularly vulnerable. Other important causes ofdeath and/orpopulationdeclineincludenecroticmange(foundinmanypopulationsofS. griseus but oddly, apparently undocumented in the introduced S. niger in California, per King 2004); habitat quality decline from removal or disruption of the forest canopy due to development, tree-cutting, or fire; soil trampling and compaction (which reduces the biomass offungi and perhaps other foods); and extremenatural events such as prolonged drought, whichwork synergistically to wipe out small populations. However, considering howmodified the current habitat ofmany lowland S. griseuspopulations is (e.g., planted pines on golfcourses), habitat transformation would seem to be a relativelyminor threat.