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photo © Merlin D. Tuttle,
Bat Conservation International.
PALLID BAT
Antrozous
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
S2). In British Columbia, the Pallid Bat is afforded complete
legal protection under the Wildlife Act. The Pallid Bat is designated
as Threatened according
to COSEWIC
(2000).
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 here 60 years ago. The first individual located was
roosting in a stone pile near Boulder Creek about five kilometres
north of Oliver in the Okanagan Valley. This single record was the
only evidence of this species in BC 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,
four Pallid Bats were captured in the vicinity of Vaseux Canyon,
and in 1990 and 1991, 12 Pallid Bats were netted in field studies
in the Okanagan region.
Distinguishing features
The Pallid Bat can be distinguished from all other Canadian bat
species by its prominent ears and eyes and its short pale (i.e.,
pallid) fur which is light brown dorsally grading 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 serrate outer edge. Compared with other Canadian
bats the eyes of Pallid Bats are relatively large. The snout is
square with a shallow ridge on top, and 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 former 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 Pallid Bats lack prominent bumps
on the nose. As well, the Pallid Bat is the only British Columbian
bat with two pairs of lower incisors.
Distribution
Map
Red dots indicate specimen records or confirmed breeding sites.
British Columbia
All Canadian Pallid Bats were found in extreme southern British
Columbia in the southern Okanagan Valley in a localized area between
Oliver, Osoyoos and Okanagan Falls. The Southern Okanagan Basin
Ecosection represents the northernmost known limit of the Pallid
Bat's distribution. It appears to be most abundant on the Inkameep
Reserve. Pallid Bats have also been captured at Vaseux Canyon and
Gallagher Bluff.
North America
The Pallid Bat is widely distributed across western United States
- southwestern US, east as far as Oklahoma and Kansas, north to
eastern Washington and Oregon, and south to the Cuba and the Mexican
states of Jalisco and Queretaro.
Habitat
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. 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 commonly-used feeding areas. The Ponderosa
Pine trees are used as night roosts and crevices in steep cliffs
for day roosts, in addition to buildings.
Rock cliffs (roosting sites) are associated with open arid habitats.
Why is it at risk?
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, and the fact that the species is at its northern-most
range limit. However, severe habitat loss in the South Okanagan
has probably impacted their numbers, especially given how colonial
species are sensitive to human disturbance. Any human activity that
disturbs bats in their night roost, day roosts, or foraging grounds
(e.g. logging, industrial activity, hiking and rock climbing), could
potentially cause Pallid Bats to move out of an area.
Habitat loss from conversion of sagebrush steppe habitat to housing
developments and golf courses, appears to be on the increase in
the Okanagan, and such development is concentrated around the lakes
and rivers in the area. The reduction of open foraging areas because
of urban development as well as grazing by cattle may degrade foraging
areas reducing prey diversity and density. Extensive irrigation
in the South Okanagan and the replacement of native vegetation with
orchards, crops, and pastures, has significantly reduced the Pallid
Bat's natural habitat. However, cliff-side roost sites are generally
secure because of inaccessibility.
Pesticides used in fruit orchards can have detrimental effects
on 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 fatty tissues and released
when 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 prey supply, but it is not known how this would affect
the abundance of the Pallid Bat.
The Pallid Bat feeds on several insect species regarded as agricultural
pests, including ten-lined june beetles, several cerambycid
beetles, crickets and grasshoppers, and moths. Given the low
abundance of Pallid Bats in the province, if any one environmental
factor changes dramatically, this could influence this species'
survival in Canada.
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, or extended winters, potentially have more significant
effects on British Columbia Pallid Bat populations than on United
States populations. Our lack of knowledge of the biology of British
Columbian Pallid Bats is the main factor limiting our ability to
protect the necessary habitat and roost sites for this species.
Although there is growing public interest towards bats, many people
are not aware of the existence of Pallid Bats in the South Okanagan.
Biology
Little is known about Pallid Bat biology in British Columbia,
but the species has been intensively studied in the southwestern
United States. Horizontal rock crevices with a hot, constant temperature
(30°C) are the preferred summer day roosts, although Pallid
Bats also roost in tree cavities, buildings, caves, and mines.
In the spring and fall, they prefer deep, vertically-oriented crevices
where temperatures fluctuate widely between cool mornings, which
initiate dormancy, to warm evenings, which awaken bats prior to
nightly emergence and foraging. During breaks in their nightly foraging
bouts, the Pallid Bats congregate in shallow caves, cliff overhangs
and shelters of buildings.
Most Pallid Bat's summer roosts contain 20 to 200 individuals
- the largest are maternal colonies. In some areas, males and females
roost separately, but in others, mixed-sex colonies exist. Males
join females after the young bats are weaned. The composition of
colonies in British Columbia is unknown, but 14 of 19 Pallid Bats
captured in the province were males, suggesting that the population
may be predominately male. Pallid Bats frequently change the location
of their day roost.
The age structure, recruitment, reproduction, immigration and
emigration, and mortality in Canadian Pallid Bat populations is
unknown. Because the British Columbia population is at the northern
extent of the species' range, recruitment may be lower than in populations
farther south.
Breeding
Pallid Bats species requires sheer cliffs with horizontal crevices
for roosting. They are believed to mate in the autumn, at communal
hibernacula, where both sexes overwinter. Mating may occur earlier
in cooler climates, such as in British Columbia, and from October
to December in the southern USA. Sperm is stored in the reproductive
tract of the female and ovulation and fertilization occurs during
the following spring.
Because time of parturition
likely is determined by local climate, the gestation
period varies, averaging about nine weeks. The only breeding
data for the British Columbian population come from a nursing female
and a male with enlarged testes,
both captured on 9 August, 1990, which suggests that young are born
in July in this province.
Pallid Bats, like most bats, have low reproductive
rates and produce one litter annually. Male and most
female Pallid Bats become sexually active in their second year.
Because the Okanagan Valley is the northern extent of the Pallid
Bat's range, the environment probably represents 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 Pallid Bats carrying
three or four embryos, but not in British Columbia. Females are
capable of breeding in their first year but yearling females bear
only one young. Young Pallid Bats are 3.0 to 3.5 grams at birth;
they are altricial 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
In summer, Pallid bats feed late in the day, leaving their day roost
about 45 minutes after sunset. Pallid Bats may commute up to 4 km
between their day roosts and foraging areas. In British Columbia,
they hunt mainly over tracts of open grassland sparsely covered
with Big Sagebrush, Rabbit Brush and Bitter-brush. Gravel roads
may provide foraging corridors - there are several observations
of Pallid Bat flying low over roads in the Okanagan.
After feeding, Pallid Bats form clusters at night roosts consisting
of exposed sites near the day roost. The roosts often are conspicuous
because of large accumulations of guano
and discarded insect fragments. In British Columbia, Pallid Bats
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 in British Columbia.
In the western United States, they are thought to overwinter near
their summer range; hibernating Pallid Bats have been found in buildings,
rock crevices, mine tunnels and caves. Most of these hibernating
records mention one or a few individuals - large winter aggregations
seem to be rare.
Pallid bats are social and produce an assortment of vocalizations
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
to attract their mothers. Swarming and calling near daytime roosts
after feeding are thought to advertise roost locations to other
members of a colony.
Pallid Bats produce 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
To feed a high metabolism,
bats consume about half their weight in insects every night. Nursing
females may eat more than their body weight each night.
Each bat species has different insect preferences and hunting
techniques. Unlike most North American bats, the Pallid Bat is a
terrestrial forager, taking large (20-70 mm), ground-dwelling or
slow-flying prey. The robust
teeth and skulls, and large body size of Pallid Bats, allows them
to take large hard-bodied invertebrates, and even small rodents,
other bats, and lizards. The Pallid Bat is an opportunistic
feeder and usually plucks prey from the ground or from
trees and shrubs, but occasionally they pursue insects in the air.
In the western United States, Pallid Bats eat large beetles, moths,
cicadas, praying mantises, katydids, grasshoppers, crickets, and
scorpions. Faecal pellets from the Okanagan Valley contained mostly
beetle parts, with traces of moths and lacewings.
While hunting, the Pallid Bat flies slowly, with rhythmic dips
and rises within a few metres of the ground. Instead of echolocating,
the desert-adapted Pallid Bat relies on rustling sounds made by
insects in areas of sparse vegetation; their hearing is so sensitive,
that they can detect the footsteps of a scorpion. Aerial prey are
tracked with both vision and echolocation. Pallid Bats eat smaller
prey when flying, and consume larger items back at the night roost.
Predators
Domestic cats and raptors, especially owls have been observed taking
Pallid Bats.
Sources for more
information
Related On-line Sites to Visit
Bat Conservation
International, Inc.
Publications
Balcombe, J.P. Status of the Pallid Bat in Canada, COSEWIC Report,
1988
Chapman, K., K. McGuiness and R.M. Brigham, Status of the Pallid
Bat, Wildlife Working Report No. WR-61, Feb. 1994
Bats of BC, RBCM, Nagorsen and Brigham, 1993
The SOCAP Workshop Summary, The Nature Trust, 1989
Bats of BC, brochure, MOE,
Bryan, A. and L. Mulholland, Species Notes and Management Options
for Fifty-four Wildlife Species of Management Concern in the South
Okangan, August 1992.
Museum Specimens
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