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Little Brown Bat
Myotis Lucifugus
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Bat Surveys at North Cascades
Bats are considered an indicator species, which means that their
presence, abundance and diversity reflects the health of an ecosystem.
A population of bats, whose numbers are stable and which includes
a diversity of species, indicates that the ecosystem is relatively
healthy. If the opposite is true, the system may be in trouble.
Several years ago biologists at North Cascades National Park determined
that they needed to gather data on the bats within the park, about
which almost nothing was known.
Researchers efforts concentrated on sampling sites in low elevation
forests, riparian areas, subalpine habitats, buildings and caves.
These areas attract bats, since they typically swoop to drink or
feed near water and in small clearings that have little vegetation
and high insect concentrations. Biologists collect data with ultrasonic
bat detectors, which record echolocation calls of bats. Experienced
researchers can identify exact species by the pattern and frequency
of their calls. They also use capture-release devices such as mist
nets and harp
traps to measure, weigh, and check the reproductive status of
captured bats.
 During
the study, biologists documented eight of the twelve species predicted
to occur in the park. They captured five species and detected three
more by ultrasonic echolocation recordings. Biologists found a ninth
species, the Townsend's big-eared bat, adjacent to the park boundary.
Other species may not have been detected due to their specialized
feeding strategies. For example, larger bats typically hunt for
insects above the canopy to avoid heavy vegetation.
By comparing bat data from different elevations, researchers have
noted some interesting patterns. Preliminary data show greater activity
in forests
and riparian
sites than at higher elevation subalpine
areas. Furthermore, capture results suggest that pregnant female
bats tend to prefer lower elevation old-growth forests for roosting
and feeding. Snags with loose, dead bark are ideal places for maternity
colonies. Because lowland forests are close to water (which insects
frequent) females can feed more efficiently and provide their young
with much needed nourishment. Above a certain elevation only males
were found, which indicates that prime lowland habitat is reserved
for nursing females who have higher caloric (energy from food) requirements.
Bats have very few natural enemies. Their dependence on wetlands
for foraging, mature trees and snags
for roosting, and caves and mines for hibernating exemplifies the
need to protect these types of natural resources.
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