The Yuma Myotis is a medium-size Myotis. Its dorsal fur varies from pale brown to nearly black; the fur on its underside is paler. The wing membranes and ears are dark brown. The ears reach the nostrils when pushed forward; the tragus is blunt and about half the length of the ear. The calcar is not keeled. The typical Myotis skull has a steeply sloped forehead.
The ear and tragus of the Yuma Myotis are smaller than that of the Fringed Myotis (Myotis thysanodes), Northern Long-eared Myotis (Myotis septentrionalis), Western Long-eared Myotis (Myotis evotis) and Keen's Long-eared Myotis (Myotis keenii). The absence of a keel on the calcar distinguishes the Yuma Myotis from the Long-legged Myotis (Myotis volans), California Myotis (Myotis californicus) and Western Small-footed Myotis (Myotis ciliolabrum). This species is most similar in external appearance to the Little Brown Myotis (Myotis lucifugus) - in some regions it can be extremely difficult to discriminate between the two. For diagnostic external and cranial criteria that identify these two bats see the account for the Little Brown Myotis.
total length: 82 (60-99) n = 322 tail vertebrae: 36 (27-45) n = 324 hind foot: 9 (6-13) n = 323 ear: 14 (8-16) n = 202 tragus: 7 (5-10) n = 212 forearm: 34.3 (30.0-38.0) n = 273 wingspan: 238 (205-260) n = 208 weight: 6.6 (4.0-8.5) n = 153
Mating occurs in autumn and in British Columbia females bear a single young between early June and mid July. Birth dates for the Squilax colony range from 5 June to 21 July with most between 18 June and 7 July. Females generally breed in their first autumn, but the age when males reach sexual maturity is unknown.
Around dusk the Yuma Myotis emerges from its day retreat to hunt over lakes, rivers and streams. Individuals from the Squilax colony travel more than four kilometres to forage over rivers and lakes. In the Okanagan Valley, where this bat mainly feeds over water, aquatic insects such as mayflies, caddisflies and midges are the major prey. Midges are main food in spring; mayflies and caddisflies are the predominant food in summer. Although food habits have not been studied in other parts of the province, aquatic insects are probably the major prey throughout its range given this species tendency to hunt over water. An efficient hunter, the Yuma Myotis can fill its stomach in 10 to 15 minutes on a productive summer night. After feeding, it retreats to a temporary night roost near the feeding area.
Its summer day roosts are usually in buildings and other man-made structures in close proximity to water; it has also been found roosting in rock crevices in the Okanagan Valley. Maternity colonies in buildings can be enormous. One of the largest known colonies of bats in British Columbia comprises 1500 to 2000 adult female Yuma Myotis in an old church on the Little Shuswap Indian Reserve near Squilax. Females with young roost in the attic under shingles and boards. Temperatures in this attic may reach 40°C in the midday heat of summer. The degree of clustering in this colony corresponds with temperature: when the air is cool females tend to pack together in close contact, but in the afternoon heat they spread out throughout the attic. The Yuma Myotis also roosts in caves and trees, but colonies in these situations are usually small. Males roost separately from females, either alone or in small groups. (Adult males are virtually unknown in the large colony at Squilax.) Various man-made structures such as house porches, abandoned cabins and bridges serve as night roosts.
Maternity colonies are deserted by late summer or early autumn. In the Squilax colony, the population begins to decline in September and by late October the roost is abandoned. The whereabouts of the Yuma Myotis in winter is unknown. Despite the local abundance of this species, no winter hibernacula have been found in the province. The only known cold-weather record for the province is from Vancouver on 27 March. In coastal Washington a few individuals have been found hibernating in caves - it is possible that similar situations are used as hibernacula in British Columbia.
This species is restricted to low elevations (sea level to 730 metres) in the province, where it inhabits coastal forests, Ponderosa Pine - Douglas-fir forests and arid grasslands.
The Yuma Myotis is found across western North America from Mexico to southern British Columbia, where it inhabits several coastal islands including Vancouver Island, the coastal mainland as far north as Kimsquit, and the interior north to the Williams Lake region and east to Nelson.
There are two races in the province: M.y. saturatus, a dark coastal subspecies ranging from California to British Columbia, and M.y. sociabilis, a paler race found in the western United States and dry interior of British Columbia.
No other bat in the province is so closely associated with water. In many locations it is the most common species captured in mist nets or bat traps set across streams and rivers. The Yuma Myotis is one of the few bats that has been observed flying over salt water in the Pacific Northwest.
There is considerable interest in preserving the large maternity colony at Squilax; this important site is listed with Bat Conservation International.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2021. E-Fauna BC:
Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab
for Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
2023-12-02 4:34:35 PM]
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