Many bats emit distress sounds when handled in the field and capturing
this vocalization is futile for the use of analyses.
I was with Joe Szewczak (creator of sonobat) in the field and he
showed me his method of recording bats in a stress free environment.
After mist netting and taking DNA, Joe ties a thin type lightweight
bungee type cord to the bat and connects this to a 50 meter zip-line.
When the bat is released the bat flies up and down the line emitting
its normal calls.
Here is a snippet with Joe explaining his method....
Effective species recognition of bats using acoustic data depends upon
representative reference calls with which to compare unknown calls.
Search phase calls comprise the most characteristic and therefore the
most useful reference calls. However, obtaining representative search
phase calls from free-flying known species has proven to be
notoriously difficult. Calls collected from hand released bats do not
provide representative free-flying calls because the bats are
accelerating, orienting and not in a steady mode of flight. Recording
calls from free-flying, light-tagged bats fulfills the requirements
for good reference calls, but in practice only a small fraction of
tagged bats ever provide an ideal pass by a waiting detector. In some
environments such as tropical forests, light-tagged bats are never
again seen once released. A tethered zip-line arrangement offers a
compromise solution for collecting reference calls from known bats. A
zip-line can be readily established in the field by stringing 30-50 m
of taut monofilament line between two poles (or other fixed objects).
The tether consists of a light, elastic line to eliminate sudden
shocks from reaching the end of the line and to gently pull the bat
back along the zip flight path if it attempts to fly laterally.
Elastic sewing thread works well for small bats. At one end, a small
loop of elastic is placed around the bat=92s neck, and the opposite end =
is attached to the zip-line using a small snap-swivel. Small stoppers
fixed to the zip-line about two m from either end prevent bats from
tangling the tether around the zip-line supports. Hanging a mini
cyalume light stick on the zip-line, to be pulled by the snap-swivel
(but not carried by the bat), aids in tracking the bat's movement and
locating the bat when it lands. The length of the zip-line enables
bats to achieve a steady mode of flight before recording calls. Many
bats will provide good flights along the zip-line on first try,
however some need several attempts before achieving steady flights.
Herein lies the advantage of the zip-line: the opportunity for
repeated flights to record satisfactory calls. Although some bats do
not produce representative calls using this method, for many bats it
yields high quality recordings comparable to free-flying bats without
the associated difficulty of recording from known free-flying bats.
Martyn
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Martyn Stewart
http://www.naturesound.org
Redmond WA
425-898-0462
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