Tamiasciurus Douglasii) in Two Mountain Ranges of the Great Basin
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Western North American Naturalist 79(1), © 2019, pp. 99–109 New records for Douglas’s squirrel (Tamiasciurus douglasii) in two mountain ranges of the Great Basin CONSTANCE I. MILLAR1,* AND KENNETH T. HICKMAN2 1USDA Forest Service, Pacific Southwest Research Station, Albany, CA 94710 2Independent Wildlife Scientist, San Carlos, CA 94070 ABSTRACT.—New records of Douglas’s squirrel (Tamiasciurus douglasii) document the species in 2 mountain ranges of the Great Basin where tree squirrels have not been previously reported, including 2 sites in the White Mountains, California, and 1 site in the Desert Creek Mountains, Nevada. In the White Mountains, squirrels were photographed by a camera trap on 9 different dates in winter and spring 2016–2017 at a site on the east side of the range crest near the Crooked Creek Field Station of the White Mountain Research Center (3125 m). In early winter 2018, two Douglas’s squirrels were observed and photographed 25 km distant and 716 m lower in Leidy Canyon (2409 m) on the lower east side of the White Mountains, 3.5 km west of the Nevada state line. In the Desert Creek Mountains, Douglas’s squirrels were observed on 4 days in autumn 2017 and winter 2018 along Desert Creek from 2005 m to 2307 m. We present evi- dence to suggest that at least the White Mountains records represent recent colonization(s) and, as such, call into con- sideration the question of how montane mammals are able to migrate into isolated mountain ranges of the Great Basin during warm Holocene climates. RESUMEN.—Nuevos registros de la ardilla de Douglas (Tamiasciurus douglasii) documentaron a la especie en dos cadenas montañosas de la Gran Cuenca (the Great Basin), donde no habían sido reportadas previamente, incluyendo dos sitios en White Mountains en California, y uno en las Montañas Desert Creek, Nevada. En White Mountains, del lado este de la cresta de la cordillera y cerca de la Central de Investigación Crooked Creek del Centro de Investigaciones White Mountain (3125 m), las ardillas fueron fotografiadas mediante una cámara trampa, en nueve fechas distintas durante el invierno y la primavera del 2016 y 2017. A principios del invierno del año 2018, dos ardillas de Douglas fueron observadas y fotografiadas a 25 km de distancia y a 716 m más abajo, en Leidy Canyon (2409 m), en la parte baja del este de White Mountains, a 3.5 km al oeste de la frontera con Nevada. A lo largo de las montañas Desert Creek desde los 2005 a los 2307 m, fueron observadas ardillas de Douglas durante cuatro días de otoño del año 2017 y de invierno del año 2018. En este estudio, presentamos evidencia que sugiere que, al menos los registros de White Mountains representan colo- nizaciones recientes, que llaman a reconsiderar cuestionamientos acerca de cómo los mamíferos de montaña fueron capaces de migrar a las cadenas montañosas aisladas de la Gran Cuenca, durante los climas cálidos del Holoceno. Douglas’s squirrel (Tamiasciurus douglasii) calls make this species easily recognizable and is a common tree squirrel of the Pacific states, familiar to many forest visitors. Douglas’s with its range extending from southern British squirrel is dependent on coniferous and angio - Columbia through south central California sperm forests due to its diet of tree parts (Fig. 1). The squirrel occurs primarily in conif- (Steele 1999). Favored forage items include erous forests of the coastal mountains and the reproductive structures of conifers and angio - Cascade Range–Sierra Nevada cordillera (Steele sperms and, especially in winter and spring, 1999). Three subspecies are recognized (Hall pine cambium obtained from tips of branches. 1981): T. d. douglasii in coastal Washington Fruiting bodies of fungi are also important in and Oregon; T. d. mollipilosus of British Colum - their diet. Douglas’s squirrels have solitary bia, the Cascade Range of Washington, and habit and aggressively defend territories cen- the Coast Range of Oregon and California; tered on larderhoards, which typically com- and T. d. albolimbatus in the Oregon Cascade prise conifer cones (Steele 1999). Range and Blue Mountains and the Sierra In California, T. d. albolimbatus occurs Nevada of California. Diurnal and nonhiber- commonly on both sides of the Cascade Range nating behavior and distinctive markings and and the Sierra Nevada (Steele 1999) where the *Corresponding author: [email protected] 99 100 WESTERN NORTH AMERICAN NATURALIST (2019), VOL. 79 NO. 1, PAGES 99–109 ° ° ° ° Fig. 1. Distribution of Douglas’s squirrel (Tamiasciurus douglasii) in western North America showing 3 subspecies and 2 zones of parapatry (bold dashed lines) with the red squirrel (T. hudsonicus). Ranges with new records (see Fig. 2) are indicated: A. Desert Creek Mountains; B. White Mountains. Modified from Steele (1999). species extends across a broad elevation range The only congener that Douglas’s squirrel following forest occurrence from the foothills contacts is the red squirrel (T. hudsonicus), into the subalpine zone (Jameson and Peeters whose range overlaps Douglas’s squirrel in a 2004). East of the Sierra Nevada, a handful of zone that extends from southern British records document the species in the Glass Columbia to northeastern Washington and a Mountains (1 record, 1942, Arctos database, small disjunct area in the Blue Mountains of accessed 1 February 2018; all Arctos records Oregon (Steele 1998, 1999; Fig. 1). The west- cited herein are from the University of Cali- ern gray squirrel (Sciurus griseus), another fornia, Museum of Vertebrate Zoology; 2012– native tree squirrel, overlaps Douglas’s squir- 2013 camera trap images, KH unpublished) rel in California west of the Sierra Nevada and the southern Sweetwater Range (7 rec- crest at elevations below 2000 m (Carraway ords, 1946, Arctos database, accessed 1 Febru- and Verts 1994, Jameson and Peeters 2004). ary 2018). The species is recorded in Nevada The western gray squirrel is known east of the only in the Carson Range (39 records, Natural Sierra crest only in the Tahoe Basin (Carson Diversity Database, Nevada Department of Range) and a few points in the vicinity of Wildlife, accessed 24 January 2018), a spur Reno, Nevada (iNaturalist database, accessed range of the Sierra Nevada. 14 March 2018). MILLAR AND HICKMAN ♦ DOUGLAS’S SQUIRREL IN THE GREAT BASIN 101 METHODS AND RESULTS region, scattered individuals of Utah juniper (Juniperus osteosperma) and pinyon pine (Pinus We encountered Douglas’s squirrel beyond monophylla) have been reported. its known distribution in 2 previously undocu- The camera, a Moultrie model m880, docu- mented Great Basin mountain ranges of Cali- mented Douglas’s squirrel on 9 different dates fornia and Nevada. Our observations are over the 8-month period (15 September 2016, serendipitous in that we made no systematic 29 September 2016, 12 October 2016, 5 Novem - searches for the species. We documented ber 2016, 14 December 2016, 19 December occurrences of the species through 3 methods: 2016, 10 March 2017, 15 March 2017, and camera trapping, handheld-camera photo- 12 May 2017; Fig. 4). In Fig. 4B a Douglas’s graphs, and indirect sign, each of which is squirrel can be seen with a limber pine cone adequate for species identification in these in its mouth. The camera also documented bob - regions (J. Patton, University of California, cat (Lynx rufus), coyote (Canis latrans), gray personal communication). A camera trap set at fox (Urocyon cinereoargenteus), yellow-bellied one location documented Douglas’s squirrel(s) marmot (Marmota flaviventris), golden-man- on 9 different dates over an 8-month period. tled ground squirrel (Callospermophilus later- In another location we photographed Douglas’s alis), chipmunks (Neotamias spp.), and mice squirrels with a handheld camera. In addition (Peromyscus spp.). to directly observing individuals, we also dis- covered indirect sign of Douglas’s squirrel in Leidy Canyon, White Mountains, regions where their range does not overlap Mono County, California with those of other tree squirrels (Steele Douglas’s squirrel was observed at 37.70249, 1999). These include distinctive vocalizations −118.21809, 2409 m elevation, in Leidy and piles of remnant conifer parts below trees Canyon, an east-facing canyon of the White where the squirrels are feeding. Conifer rem- Mountains, California and Nevada (Fig. 2B). nants include scales and chewed cores of cones Extending to the crest of the range, the Leidy and clipped branch tips lying directly below watershed originates north of White Mountain tree crowns. No other bird or animal leaves Peak (4333 m), the high point of the range. such sign in this location and abundance. Leidy Creek is intermittent in its upper reaches Our observations document 3 new locations: but attains perennial condition where Cabin 2 point sites in the White Mountains of Cali- Creek joins it. Leidy Creek drains into Fish fornia and 1 band that extends from the Desert Lake Valley, Nevada, which is a large evapora- Creek Mountains into the northern tip of the tive basin with base elevations of ~1500 m. Sweetwater Mountains, Nevada. The following The upper slopes of Leidy Canyon (above are details about each site. 2500 m) support forests of bristlecone pine and limber pine while foothill slopes contain Crooked Creek, White Mountains, pinyon pine–Utah juniper woodlands. A rare Mono County, California stand of lodgepole pine (Pinus contorta) occu- Douglas’s squirrel was documented by pies subalpine elevations (above 3100 m) along camera trap at 37.49749, −118.17015, 3125 m Cabin Creek, north of Leidy Canyon. elevation, in a gully 220 m southeast of Crooked Two Douglas’s squirrels were observed on Creek Station (Figs. 2B, 3A). The camera trap 5 January 2018 in the riparian zone of Leidy was one of 4 set around Crooked Creek Station Creek, 3.5 km west of the Nevada state line during winter and spring 2016–2017 as part of and coincident with the first crossing (in the a coyote study, and the only camera trap to upstream direction) of the dirt track that document Douglas’s squirrels.