265.

Western Yellow Bat

Lasiurus xanthinus

French: Lasiure de Californie / German: Westliche Haarschwanzfledermaus / Spanish: Lasiuro de California

Taxonomy. Dasypterus ega xanthinus Thomas, 1897,

“Sierra Laguna, Lower California [= Baja California],” Mexico.

Lasiurus xanthinus was previously considered a subspecies of L. ega, but studies based on allozymes and restriction-enzyme analysis of mtDNA suggested that L. xanthinus should be treated as a distinct species. Recent molecular studies based on mtDNA and nDNA also recovered L. xanthinus as a full species and placed it as the most basal lineage in the Yellow Bat group. Monotypic.

Distribution. SW USA (S California, S Nevada, Arizona, SW New Mexico, and SW Texas) S to W & C Mexico.

Descriptive notes. Head—body 61-76 mm, tail 40-50 mm, ear 11- 9-19 mm, hindfoot 8-10 mm, forearm 42-48 mm; weight 12-19 g. Dorsal hairs have dark bases and pale yellowish tips, lightly washed with black. Ventral hairs are bicolored, with blackish bases and reddish yellow tips. Ears are short, wide, naked, and light brown. Tragusis broad and reaches slightly more than 50% the ear length. Face is dark brown, not black. Uropatagium is densely furred, with bright yellow hairs that contrast with dorsal fur. Skull is short and broad; rostrum slopes in front and almost aligns to braincase, which is high and rounded; auditory bullae are well developed; zygomatic arches are slender; and basisphenoid pits are distinct, long, and narrow. I? is close to C', unicuspid, and pointed; P? is absent; M' and M? lack hypocone; M? is reduced; lower incisors are tricuspid and almost perpendicular to jaws; and lower molars have developed cusps. Dental formulais 11/3, C1/1,P 1/2, M 3/3 (x2) = 30. Chromosomal complement has 2n = 28 and FN = 46, with seven pairs of large metacentric and submetacentric autosomes, three pairs of medium metacentric autosomes, three pairs of small acrocentric autosomes, medium submetacentric X-chromosome, and small acrocentric Ychromosome.

Habitat. Semiarid to arid areas, including xeric shrublands, palm groves, riparian woodlands, savannas, pastures, and croplands at elevations of 25-2400 m (more often at intermediate elevations). The Western Yellow Bat is often captured over water (e.g. streams, ponds, stock tanks, and rivers) and in open areas, canyons, and riparian areas.

Food and Feeding. The Western Yellow Bat has been recorded flying slowly and steady at 9-23 m aboveground and rapidly along arroyos. Feces contained species of Coleoptera, Diptera, Hemiptera, Hymenoptera, Homoptera, Lepidoptera, and Orthoptera .

Breeding. Pregnant Western Yellow Bats usually bear two embryos and were captured from early May to mid-July, lactating females from late June to late July, and young from mid-July to September.

Activity patterns. The Western Yellow Bat is crepuscular/nocturnal. Individuals were observed flying before dusk and captured during the first five hours of dark. In winter, it can reduce activity, suggesting periods of torpor. Roosting sites are mainly found in dead-leaf skirts of palm trees but also hackberry, sycamore, cottonwood, and vines. Roosting sites have been found 2- 2 m aboveground and 4 m above a road. Echolocation calls are c.6-9-2 milliseconds, with narrowband and single harmonic, and sweep from 52-68 kHz to 26-30 kHz.

Movements, Home range and Social organization. The Western Yellow Bat is usually solitary, but small groups can be found. It was observed only during autumn in northeastern parts of its distribution, suggesting southward seasonal migration. In northern parts ofits distribution, some individuals are present throughout the year.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Western Yellow Bat is widespread, presumably has a large population, and occurs in several protected areas. Major threats are use of pesticides, fires, and trimming of palm trees.

Bibliography. Aguilar et al. (2014), Alvarez-Castafieda & Gonzalez-Ruiz (2018), Arroyo-Cabrales & Alvarez-Castaneda (2017b), Baird et al. (2015), Baker & Patton (1967), Baker, Patton et al. (1988), Bickham (1987), Collen (2012), Constantine (1946), Handley (1960), Higginbotham, Ammerman & Dixon (1999), Higginbotham, Dixon & Ammerman (2000), Kurta & Lehr (1995), Leén-Tapia & Hortelano-Moncada (2016), Morales & Bickham (1995), Morgan et al. (2019), Novaes, Garbino et al. (2018), O'Farrell et al. (2004), Ortiz & Barrows (2014), Simmons (2005), Thomas (1897a), Williams et al. (2006).