Vision in echolocating bats - Fladdermus.net

dish was recorded as a foraging attempt, and as soon as a landing was recorded
the arrangement of the feeding situation was changed. To prevent the bats from
using spatial memory the experimental area was divided in two parts (A & B),
which were used alternately, so that a foraging attempt in area A was followed
by an experiments in area B. The light sources could be placed at four different
positions within each area, and the positions were changed at random after each
feeding attempt. Also the arrangement of the four petri dishes (presenting the
different sensory cues) was changed at random after each feeding attempt.
Hence, in total there were 32 potential positions for each petri dish.
An infra red sensitive video camera (Sony Mini DV TRV9E
Handycam) with a wide-angle lens was placed above the experimental area. It
was connected to a monitor placed outside the flight room and thus making it
possible to survey the experiments without disturbing the bats.
In order to test if the probability of a feeding attempt at a certain
dish was the same for all bats, i.e. if we could treat the bats as one group, we
applied a Chi square test of homogeneity (testing if a specific distribution is the
same in different situations, in this case for the different bat individuals). Then
we made pair-wise comparisons between dish preferences, i.e. we compared the
probability that one dish was preferred over another. We did so by using 95%
confidence intervals, i.e. intervals having 95% probability of covering our
estimated preferences (number of captures in each category divided by total
number of captures) for the different feeding dishes. As we calculated several
intervals using the same data set, we applied the Bonferroni method for multiple
comparisons.
Experiment 2
To exclude the possibility that the bats considered the light or the petri dishes
rather than the actual prey items as potential food sources, we presented the bats
with two lit areas, one with a petri dish containing mealworms, and one with an
empty dish. The set-up was similar to the one in experiment 1, although only one
light source (with two goose necks) was used, and this time all four bats were
flying simultaneously. We also placed a bat detector (Ultra Sound Advice S-25
set in frequency-division mode) next to one of the petri dishes, and connected it
to a speaker outside the flight room. The different positions of the light source
and the arrangement of the two petri dishes together with the position of the bat
detector, were changed after each feeding attempt and randomised in a similar
manner as in experiment 1. This experiment was also surveyed using an IR
sensitive video camera. The number of feeding attempts at the two petri dishes
was compared using Chi square statistics, and echolocation calls from feeding
bats were noted.
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