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photo © Merlin D. Tuttle, 
PALLID BATAntrozous pallidus Family Vespertilionidae - Vespertilionid Bats Order Chiroptera - Bats Risk Status Official status The Pallid Bat is one of the rarest mammals in British Columbia and is therefore on the Provincial Red List (CDC G5 S1). In British Columbia, the Pallid Bat is afforded complete legal protection under the Wildlife Act. The Pallid Bat is designated as Vulnerable.
Image Credits: photo © Merlin D. Tuttle, Bat Conservation International. Sketch in Bats of British Columbia, Nagorsen and Brigham, 1993. Historical facts Present status of the Pallid Bat in British Columbia is unknown. Only 19 individuals have been captured in British Columbia since its discovery in the province 60 years ago when Ian McTaggart-Cowan and Ken Racey found an individual roosting in a stone pile near Boulder Creek about five kilometres north of Oliver in the Okanagan Valley, British Columbia This was the only evidence for this species in the province until 1974 when a dying Pallid Bat found at Okanagan Falls was submitted to the Federal Agriculture Laboratory to be tested for rabies. In the late 1970s and 1980s, Brock Fenton and Robert Herd captured four Pallid Bats in the vicinity of Vaseux Canyon in the Okanagan. Then, in 1990 and 1991, 12 Pallid Bats were netted in field studies conducted by Mark Brigham and his students. The Pallid Bat can be distinguished from all other Canadian species by its prominent ears and eyes and its short pale (i.e., pallid) fur which is light brown dorsally and tending towards white on the underside. Individual hairs are pale at the base with darker tips. The pale ears are broad and extend well beyond the nose when pushed forward; the tragus is long and narrow, with a toothed outer edge. Compared with other Canadian bats the eye are relatively large. The snout is square with a shallow ridge on top; the end of the snout is scroll-shaped. They have several wart-like bumps across the facial region. The calcar lacks a keel. The skull is large with heavy, robust teeth. The only species the Pallid Bat could be confused with is Townsend's Big-eared Bat; but the Pallid Bat is much larger (forearm length between 48-57.4 mm; mass 13.6-28.9 g), with large prominent ears that are not joined at their bases and lacking the two prominent bumps on the nose. As well, the Pallid Bat is the only British Columbian bat with two pairs of lower vincisors.
Map
British Columbia
North America The Pallid Bat is found in arid desert habitat in British Columbia, often near rocky outcrops and water. It is restricted to low elevations (300-490 metres) in sagebrush steppe areas and Ponderosa Pine forests in the vicinity of cliff faces and water. Preferring to forage in open areas, the Pallid Bat can be found over lengthy tracks of sandy, sparsely vegetated sagebrush and grassland. Gravel roads and canyon mouths are preferred feeding areas. The Ponderosa pine trees are preferred as night roosts and steep cliffs for day roosts. Generally, they will day roost in crevices, chambers in rock cliffs or in buildings. Rock cliffs (roosting sites) are associated with open arid habitats. It seems likely that Pallid Bats have always been rare in the Canadian portion of their range because of restricted habitat and a less than ideal climate and low recruitment. However, severe habitat loss in the South Okanagan has probably further limited their numbers. Colonial species are sensitive to human disturbance. Any human activity that disturbs the bats in their night roost, day roosts, or foraging grounds, could potentially cause Pallid Bats to move out of the area including logging, industrial activity, hiking and rock climbing. Habitat loss from conversion of sagebrush steppe habitat to other uses such as housing developments and golf courses appear to be on the increase in the Okanagan. The reduction of open foraging areas because of development as well as grazing by cattle may degrade foraging areas reducing prey diversity and density. Roost sites are generally secure because of inaccessibility however. Pesticides are used extensively in Okanagan fruit orchards and potentially have detrimental effects on the Pallid Bat populations. Because of the climate in British Columbia, Pallid Bats may suffer more from ingesting pesticides than Pallid Bats farther south. Pesticides are stored in the fatty tissues and are released when the fat is metabolized. The effect of ingested pesticides is probably worst during severe cold because more fat reserves are used during hibernation and migration. In addition, pesticides and herbicides may limit the prey supply, but it is not known how this would affect the abundance of the Pallid Bat. Lack of knowledge about the biology of the British Columbia populations is a factor affecting the ability to protect the necessary requirements required to sustain breeding populations of Pallid Bats. Although there is growing public sympathy towards bats, many people are not aware of the existence of Pallid Bats in the South Okanagan. Public interest could be generated if the economic benefits of this species were advertised. The Pallid Bat feeds on several insect species regarded as agricultural pests, including ten-lined june beetles, whose larvae feed on the roots of fruit trees; several cerambycid species, whose larvae often ruin cut logs; crickets and grasshoppers, which damages crops and wild plants; and moths, whose caterpillars destroy foliage. More research is required if management is to be instituted. Given the low abundance of this species in the province, any one environmental factor that is dramatically changed could influence this species' ability to persist in Canada. Biogeoclimatic factors must be such that Pallid Bats can raise their young and store sufficient energy in time to migrate south and/or hibernate for the winter. Environmental conditions in British Columbia are not as suitable for Pallid Bats as they are in the United States. Thus cycles of prey density and climatic factors, such as cold, rainy summers, potentially have more significant effects on British Columbia Pallid Bat populations than on United States populations. If the British Columbia population remains in the Okanagan to hibernate, long or severe winters would affect Pallid Bat numbers. Extensive irrigation in the South Okanagan and the replacement of vegetation adapted to an arid climate with orchards, crops, and pastures has significantly reduced the Pallid Bat's natural habitat. Little is known about its biology in British Columbia, but it has been the subject of intensive study in the southwestern United States. Horizontal rock crevices with a hot, constant temperature (30°C) are the preferred summer day roosts, although it has also been found roosting in tree cavities, buildings, caves, mines and crevices in cliffs.
A gregarious bat, most of the Pallid Bat's summer roost comprise 20 to 200 individuals - the largest are maternity colonies. In some areas, males and females roost separately, but in others, mixed colonies containing both sexes have been found. The males join the females after the young bats are weaned . The composition of colonies in British Columbia in unknown, but 14 of 19 Pallid Bats captured in the province were males, suggesting that the population may be predominately male. It appears that Pallid Bats frequently change the location of their day roost. The age structure of Pallid Bats in unknown. Nor does information exist regarding recruitment and mortality in Pallid Bats. Because the British Columbia population is at the northern extent of the Pallid Bat's range, recruitment may be lower than in populations farther south. The growth potential of the population in British Columbia is not known as are factors that may influence abundance, such as natality, mortality, immigration and emigration.
Breeding Pallid Bats are believed to mate at hibernation sites, where both sexes overwinter, during late fall prior to postbreeding dispersal. Breeding may occur sooner in cooler climates, such as that in British Columbia. Sperm is stored in the reproductive tract of the female and ovulation occurs during the following spring. Because time of parturition is likely determined by local climate, the gestation period is variable, but averages about nine weeks. The only breeding data for the British Columbian population are a nursing female and a male with enlarged testes, both captured on 9 August, 1990, which suggests that young are born in July. In the southwestern United States mating takes place from October to December. Pallid Bats, like most bats, have low reproductive rates and produce one litter annually. Male and female Pallid Bats become sexually active in their second year of life. Because the Okanagan Valley is the northern extent of the Pallid Bat's range, the habitat is probably at the limit of this species' tolerance resulting in litters of only one or two young, with twins most common. There are a few records of females carrying three or four foetuses (1-2 in British Columbia). Females are capable of breeding in their first year but yearling females can bear only one young. Young weigh 3.0 to 3.5 grams at birth; they are undeveloped and their eyes are closed. In four or five weeks they are capable of short flights and by eight weeks they attain adult size.
Behaviour After feeding, Pallid Bats form clusters at night roosts which are exposed sites near the day roost. They are often conspicuous because of the presence of large accumulations of guano and discarded insect fragments. In British Columbia, this bat seems to prefer Ponderosa Pines for night roosts where, if the temperatures are cool, they become torpid for several hours. Individuals found together at a night roost may occupy separate day roosts. There are no winter records of Pallid Bats for the British Columbia. In the western United States this species is thought to overwinter in the general vicinity of its summer range. Hibernating Pallid Bats have been found in buildings, rock crevices, mine tunnels and caves. Most of these hibernating records are of one or a few individuals - large winter aggregations seem to be rare. A social bat, this species produces an assortment of vocalizations for communicating in a colony. These calls, most of which are audible to humans, are used in territorial disputes, for directing individuals to a roosting site and in mother-infant communication. Newborns also emit calls that may assist mothers in locating them. Swarming and calling near daytime roosting sites after the bats return from feeding are thought to advertise roost locations to other members of a colony. The Pallid Bat produces a musky skunk-like odour from glands on the muzzle. There have been no experimental studies to determine the function of this odour - it may be a defensive mechanism for repelling predators.
Diet or Growing requirements Each species has different insect preferences and hunting abilities. Unlike most other North American bats, the Pallid Bat is a terrestrial forager, taking large (20-70 mm), ground-dwelling or slow-flying prey. The Pallid Bat is well adapted for killing and eating large hard-bodied invertebrates with its robust teeth skull and its large size. The Pallid Bat is an opportunistic feeder and usually gleans prey from the ground and the foliage of trees and shrubs, but it occasionally pursues insects in the air. In the western United States the Pallid Bat eats june beetles, moths, cicadas, praying mantises, katydids, grasshoppers, scorpions and crickets. There are also records of this bat preying on vertebrates such as small lizards, desert Pocket Mice and smaller bats in captivity. Faecal pellets from the Okanagan Valley contained mostly beetles; moths and lacewings were minor prey items. While hunting, the Pallid Bat flies slowly, within a few metres of the ground, with rhythmic dips and rises. Instead of echolocating, the desert-adapted Pallid Bat relies on sounds made by its prey to locate and capture a meal - often crickets or scorpions. While hunting prey on the ground it listens for their rustling sounds over large areas of sparse vegetation. Aerial prey are tracked with both vision and echolocation and can be so sensitive as detect the footsteps of a scorpion. The Pallid Bat eats small prey while it is flying, but consumes larger items back at its night roost.
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