372.

Western Small-footed Myotis

Myotis ciliolabrum

French: Murin pygmée / German: Westliches Kleinful 3-Mausohr / Spanish: Ratonero pigmeo

Taxonomy. Vespertilio ciliolabrum Merriam, 1886,

“near the town of Banner,” Trego County, Kansas, USA.

Subgenus Pyzonux; lucifugus species group. Populations of M. ciliolabrum were previously called M. keenii, M. leibir, M. subulatus, and M. melanorhinus . Monotypic.

Distribution. From SE Alberta and SW Saskatchewan (Canada) S to SC USA, including E Idaho, Montana, SW North Dakota, Wyoming, W & S South Dakota, NE Utah, E Colorado, Nebraska, W Kansas, and extreme NE New Mexico.

Descriptive notes. Head-body ¢.39 41 mm, tail 37-49 mm, ear 12-16 mm, hindfoot 6-9 mm, forearm 31:2-35- 7 mm; weight 3-6 g. Females are slightly larger than males. The Western Small-footed Myotis is morphologically similar to the Eastern Smallfooted Myotis (M. leibir) and the Dark-nosed Small-footed Myotis ( M. melanorhinus). Fur is long and silky. Pelage is generally paler than in other North American Myotis . Dorsal hairs are bicolored, with blackish bases and flaxen to pale yellow tips; ventral hairs are is slightly paler, with dark brown bases and light yellow or nearly white tips. Ears are moderately long and extend slightly beyond nose when laid forward; tragus is long and narrow, being ¢.50% of ear length. Membranes, ears, and skin are blackish. Plagiopatagium is attached to feet by a broad band of membrane; calcar is distinctly keeled. Skull is moderate in size (greatest skull lengths 13-5-14- 7 mm), and compared with the Eastern SmallHfooted Myotis, the Dark-nosed Small-footed Myotis, and the California Myotis ( M. californicus), the Western Small-footed Myotis hasless steeply sloping frontal bone, flatter and broader skull, and greater rostral breadth. Parietal is normally inclined forward; occipital is rounded posteriorly; braincase is flattened; sagittal crest is generally absent but, when present,is very low; and lambdoidal crests are generally present and low. Chromosomal complement has 2n = 44 and FN = 50, with four pairs of metacentric and 17 pairs of acrocentric autosomes. X- and Y-chromosomes are submetacentric.

Habitat. Grasslands with rock outcrops, coniferous forests, deserts, and dry shrublands, at elevations of 300-3300 m. Along the Rockies and adjacent plains, Western Smallfooted Myotis are generally found in broken terrain of canyons and foothills, commonly in places with cover of trees or shrubs.

Food and Feeding. The Western Small-footed Myotis is an aerial insectivore that forages only c. 1 m aboveground;it flights is erratic and slow. One-half of its foraging time is spent near rocks and cliffs and the remainder over open areas, forest canopy, and water. Diets contain Lepidoptera but also Diptera, Hemiptera, Hymenoptera, and Coleoptera .

Breeding. The Western Small-footed Myotisis polygynandrous and reproduces seasonally, generally starting in early July. Mating season begins shortly before hibernation, and females store sperm until spring when ovulation and fertilization occur. Gestation lasts ¢.2 months. Most females give birth to one young, but twins have been reported. Parturition seems to occur in July-September. Sexual maturity typically occurs at just over a year of age.

Activity patterns. The Western Small-footed Myotis begins foraging before full dark, and activity is concentrated in the three first hours of the night. It hibernates from early autumn through winter. It roosts in rock crevices,cliffs, abandoned mines, caves, and occasionally tunnels and buildings and under tree bark and rocks scattered on the ground. In Wyoming, calls had mean maximum frequency of 62-4 kHz, minimum frequency of 40-3 kHz, and duration of 3-5 milliseconds.

Movements, Home range and Social organization. While foraging, no Western Smallfooted Myotis were reported further than 1 km from their roost or foraging areas. Western Small-footed Myotis tend to be more solitary than congeners. In summer, pregnant females form maternity colonies of up to 20 individuals (adults and young), but sometimes they are solitary.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Western SmallHfooted Myotis is widespread, common over most of its distribution, occurs in protected areas, and is unlikely to be declining at nearly the rate required to qualify for listing in a threatened category.

Bibliography. Armstrong et al. (2011), Arroyo-Cabrales & Alvarez-Castafeda (2017h), Halloway & Barclay (2001), Landry (2004), O'Farrell et al. (1999), Simmons (2005), Wilson & Ruff (1999).