Individual populations of spotted bats are apparently disjunct and may be vulnerable to human disturbance. Population trends, life history, and habitat requirements are unknown.
Description and Range
The spotted bat is one of the larger bat species in Washington and is easily recognizable by its black dorsal fur with two large white spots on the shoulders and one on the rump. Smaller white patches occur at the base of the ears, and the belly is whitish with black underfur. Individual hairs are short, pale at the base, and darker brown or grey at the tips. Wing membranes are pinkish-red to grey-brown in color. A bare patch, circular in shape and non-glandular, occurs on the throat and may be hidden beneath the fur.
The long pinkish ears are joined at their bases across the forehead and have transverse ribs extending to their rear edge. A fringe of fine hairs extends along the top border on the back of the ears. The tragus is long and broad, and the calcar is not keeled. Spotted bats produce a low-pitched (6-16 kHz) echolocation call that is audible to people and distinctive from other bats in Washington.
Food Habits and Foraging
The diet consists primarily of medium-sized moths, especially noctuid moths. Spotted bats use low frequency echolocation calls to find prey. Emergence from day roosts often occurs during the first hour after sunset. Spotted bats may use the same commuting paths night after night. Commuting distances between day roosts and feeding areas can range from 1 to 39 km depending on the proximity of suitable areas. Spotted bats appear to use a “trapline” foraging strategy, whereby individuals forage at several sites during an evening and consistently return to these same sites on consecutive nights. Foraging usually occurs within 50 m of the ground. Although bat species with large ears are typically associated with a gleaning foraging strategy, evidence of gleaning by spotted bats has not yet been found. Spotted bats have been observed hunting alone and individuals using adjoining foraging grounds appear to avoid each other, which may reduce intraspecific competition.
In Washington, spotted bats have been detected foraging and/or traveling over rock cliffs, talus slopes, sagebrush-bunchgrass, open ponderosa pine-bunchgrass, riverine habitat, open water, deciduous copses, and a golf course. Other foraging habitats noted in British Columbia and Oregon include ponderosa pine forests, old fields surrounded by ponderosa pine forest, Douglas fir uplands usually in close proximity to wetlands or rivers, juniper forest, irrigated fields, marshes adjacent to lakes, and abandoned pastures within 10 km of cliffs.
Reproductive habits are not well known. Like most other temperate vespertilionids, spotted bats likely mate in the late summer or fall. Reproductive data from the northern part of the species’ range suggest that young – one per year – are born from mid-June to early July. Females are believed to give birth while roosting alone rather than becoming communal. Age of sexual maturity is unknown, but probably occurs by the first autumn in both sexes.
Spotted bats occur in much of western North America from south-central British Columbia and southern Montana south to central Mexico. The core area of the species’ distribution appears to be the southwestern U.S. Spotted bats have been recorded in seven counties in eastern Washington. Highly anomalous records from Woodway, Snohomish County, in 1997 and Seattle in November 2008 probably represent accidentally transported individuals.
Spotted bats occupy habitats ranging from desert and shrub-steppe to montane coniferous forest and meadows. The species is more closely associated with high sheer cliffs, which are required as day roosts, than specific vegetation types. In Washington and adjoining areas, spotted bats have been found using a variety of habitats, including ponderosa pine forest, Douglas-fir forest, forest openings, shrub-steppe, hayfields, cliffs, talus slopes, marshes, open water, riparian forests, and golf courses. Elevations from below sea level to 3,230 m are used across the species’ range, but in Washington, occupied sites vary from 300 to 850 m in elevation.
Spotted bats roost extensively in the crevices of steep cliffs, but have been noted to use caves and buildings as well. Availability of day roosting habitat in cliffs is often believed to limit the species’ distribution and population size. In Washington, high (>30 m) vertical cliffs of granitic gneiss or columnar basalt are used as day roosts. Warm aspects are favored at sites with light colored granitic rock, whereas cool aspects are used on dark basalt cliffs. Spotted bats probably roost solitarily, with the exception of mother-young pairs. However, loose aggregations may form in areas with abundant roost crevices, such as at Moses Coulee and McGlaughlin Canyon in eastern Washington.
Night roosts are used in some locations, but not at others. Use probably depends on availability of nearby day-roosting sites and differences in foraging behavior. Night roosts have been located in caves and aspen groves.
Hibernacula and wintering behavior are poorly known in much of this species’ range. Spotted bats are active in low-elevation canyons in Oregon from as early as February to as late as October, suggesting hibernation occurs during the remaining months.
Sensitivity to climate change
The spotted bat occupies a range of habitats in Washington from shrub-steppe and forests (e.g., ponderosa pine, Douglas-fir) to cliffs and water sources (e.g., marshes, open water, riparian areas) from 300 to 850 m in elevation. They appear to roost almost exclusively in the crevices of steep cliffs. There is limited information about this species' population size and trends and reproductive and wintering behavior, although there is some evidence that the spotted bat moves to lower elevations to overwinter. Changes in precipitation that limit the availability of water sources or result in a decrease of prey could negatively affect this species. Increased fire and shrub-steppe degradation (including greater occurrence of cheatgrass and other invasive plants) in the Columbia Basin could also reduce habitat quality for this species.
Exposure to climate change
- Changes in precipitation
- Altered fire regimes
- Increased invasive species
- Surveys of potential roosting and foraging habitat are needed to gain a better understanding of the distribution and potential threats to this species.
- At sites where presence is documented, habitat and water sources should be identified and mapped.
- Winter roost sites are unknown and should be located. Given the rarity of this bat in Washington, scientific collection could pose a threat to local populations and should be restricted by WDFW.
- Outreach to recreational climbing organizations about the effects of climbing on bat populations may be necessary in some locales to prevent disturbance.
- Pesticide applications proposed for areas used by spotted bats should identify foraging and roosting areas and water resources at project sites and avoid spraying in these areas.
- Bat mortalities at wind energy facilities in Washington should be monitored for this species.
For some people bats don't present a problem. For others, bats can be a worry, especially when they become unwanted guests in an attic, inside a wall of a home, or inside the home itself.
Unlike rodents, bats only have small teeth for eating insects, so they do not gnaw holes in walls, shred material for nests, chew electrical wiring, or cause structural damage to buildings. Damage caused by bats is usually minimal, but they can be noisy and alarming, and the smell of bats and their droppings can be offensive. It is possible to learn to coexist with bats, and to benefit from their presence. Learn more on our Living with Wildlife: Bats webpage.