202.

Canyon Bat

Parastrellus hesperus

French: Parastrelle de |' Ouest / German: \Westliche Amerikanische Zwergfledermaus / Spanish: Parastrelo del oeste

Other common names: \\ Western Pipistrelle

Taxonomy. Scotophilus hesperus H. Allen, 1864,

Old Fort Yuma, Imperial County, California, USA.

Has variously been placed in Scotophilus, Vesperugo, Pipistrellus, and Hypsugo, but morphological, karyological, and molecular data support its separation in a monotypic genus, Parastrellus . Monotypic.

Distribution. W & SW USA (SE Washington S to SW Oklahoma and W Texas) and Mexico as far S as Guerrero.

Descriptive notes. Head-body c.34-53 mm, tail 25-36 mm, ear 11-14 mm, hindfoot 7-10 mm, forearm 26-33 mm; weight 2-6 g. Females larger than males. Fur is silky and dorsal hairs are bicolored, with blackish or dark brown bases, and tips ranging from smoky gray brown to yellowish brown or pale orange yellow; ventral hairs are bicolored, with blackish bases and tips ranging from pale yellowish to whitish, with a strong contrast between bases and tips. Ears are short; tragus is blunt, slightly curved, and usually one-half of ear height. Hindfoot is short, less than one-half tibia length; calcar is keeled; wing membrane attaches at base of toes. Dorsum of uropatagium is thinly furred on basal one-third; membranes are blackish, contrasting strongly with pelage. Baculum is inflated dorsally, forming a broad, roof-like support for extensive distal enlargement of glans penis (with trilobate globular bodies). Skull is small (greatest skull length 11-3-13-1 mm) and nearly straight in dorsal profile; braincase low, but broad and elongated; postorbital region wide; supraorbital area slightly widened; rostrum short, not conspicuously expanded, and with shallow median depression where rostrum merges with frontals;slight lateral-rostral depressions just above anteorbital foramina; premaxillae are not shortened; cranial profile almost straight, slightly depressed above anterior root of zygomata; zygomata slender,a little widened anteriorly, and lacking anyjugal eminence; interdental palate is about as wide as long; maxillary tooth rows convergent; short bony post-dental palate; basioccipital is narrow; cochlear bullae are inflated. Dental formulais12/3, C 1/1, P 2/2, M 5/35 (x2) = 34. Chromosomal complement has 2n = 28 and FN = 46, with nine medium-sized to large metacentric and submetacentric pairs of chromosomes, one small submetacentric, three small acrocentric, a medium-sized submetacentric X-chromosome, and a small acrocentric Y-chromosome.

Habitat. Mainly associated with rocky outcrops near permanent water in lowlands, but also found at altitudes up to 2800 m. Occurs in Xeric vegetation (e.g. desert, grassland, shrub-steppe) and woodland adjacentto arid areas (e.g. coniferous, oak, juniper, and riparian forests).

Food and Feeding. Forages at 2-15 m aboveground or over water, where it captures small insects in flight. Diet includes Hemiptera, Hymenoptera, Lepidoptera, Diptera, Coleoptera, Homoptera, Tricoptera, and Plecoptera; soft-bodied insects are preferred.

Breeding. Copulation and insemination occur for first time in autumn; sperm may be retained within female through winter; males continue to produce sperm during winter, and winter copulations may be essential to guarantee spring fertilization. Pregnant females are found in May and June; gestation lasts ¢.40 days. Young are born in June and July, usually two but sometimes only one. Maternity colonies may be established in buildings or rock crevices. Weaning occurs at around one month of age, when young are difficult to distinguish from adults.

Activity patterns. Foraging activity begins very early in evening, making this species one of the most diurnal bats of North America. It is most often netted during first hour or two after sunset and then not again until near dawn. Occasionally, individual bats fly around midday, when they seek water to alleviate stress caused by the arid environment. Diurnal roosts include crevices of canyon walls,cliffs, under rocks, caves, human buildings, and dense growths of sedge. In winter, these bats hibernate in mine tunnels and caves.

Movements, Home range and Social organization. The Canyon Bat is not a strong flier and, predictably, is not migratory. It has a slow, fluttery flight, which restricts it to small foraging circuits. It is only modestly colonial, and solitary individuals are typical. Maternity colonies are small, not exceeding twelve individuals, including adult females and juveniles.

Status and Conservation. Classified as Least Concern on The IUCN Red List, because of its wide distribution, occurrence in a number of protected areas, and presumed large population; it is unlikely to be declining.

Bibliography. Allen (1864), Baker & Patton (1967), Findley & Traut (1970), Hall (1981), Hatfield (1936), Hill & Harrison (1987), Hoofer et al. (2006), Schmidly & Bradley (2016), Simmons (2005), Solari (2019e), Wilson & Ruff (1999).