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The frequency and amplitude of the bat call have a major influence on how far away the call
can be detected, and makes some species easier to detect from afar than others. Quiet (low
amplitude) and high frequency bat calls are more difficult to detect than loud (high
amplitude) or low frequency calls. Call amplitude can vary within an individual, as many bats
will reduce the amplitude of their calls as they approach prey or depen ding on the context in
which they are flying. Call amplitude can also vary between species. Species which always
produce low amplitude calls (
‘
whispering bats
’
) will be more difficult to detect from a distance
than other species. In addition, bat calls of higher frequencies cannot usually be detected
from as far as those of lower frequencies, as higher frequencies suffer greater absorption by
the atmosphere than lower frequencies.
Atmospheric absorption depends upon weather conditions such as temperature, h umidity
and air pressure. This relationship is complex, but in general, cool dry conditions will allow
the detection of bat calls over greater distances.
The sensitivity of the recorder also has a major influence on detection distance, and while
there is always some variability in sensitivity among units, the biggest influence is the
sensitivity setting.
Given all the above, it is obvious that detection distances will vary enormously. Many bats are
easily detected over 30m under typical conditions, while some species which call at low
frequencies may be detectable from as far as 100m. However, some species will be hard to
detect from even 1m away. This is why activity levels measured acoustically cannot easily be
compared between different species. However, acoustic indices of activity are generally much
less biased than indices based on capture data.
Further information on detection distances and the calculation of detection fields and
distances can be obtained from the software AnaVolumes (you can download at www.titley-
Can I use the Chorus as an active recorder?
While the Chorus is designed as a passive recorder, it can be used as an active recorder by
connecting your headphones. You can also use the built-in GPS to log your track using the
function.
Summary of Contents for CHORUS
Page 1: ...CHORUS User Manual Version 1 0 ...
Page 7: ...7 EXTERNAL FEATURES ...