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Fig. 2. The predictive start of archer fish. (A) After the shot of a group member
has just dislodged an aerial insect, a responding fish (lower right) turns
from its initial orientation (dotted line) and takes off directly towards the
later point of impact, with a speed matched to distance. Because the initial
values of prey motion (initial height, speed and take-off angle) vary
independently over broad ranges, predicted points P of impact can be anywhere
within a large area. They must be inferred from a quick judgement of the
prey's initial motion, based on which the fish must rapidly select an
appropriate turn (angle 
) and take-off (speed v). The match that
the responding fish must make is illustrated by showing three ways (in
different colors) in which a given shot might dislodge the target insect. The
correspondingly different impact points P1-P3 (shown in
the respective colors) would require speed levels
v1-v3 and turning angles
1-3. Responses aimed at P1 and
P2 would require different turns but the same take-off speed,
whereas responses to P2 and P3 would require the same
turn, but different take-off speed. (B) The actual turning range and accuracy
in the set of predictive starts (N=76) whose kinematics are analyzed
in this study using digital high-speed video. Turns were accurately set to the
later point of impact and accuracy did not decrease when larger turns were
required. The regression line (r2=0.9016,
P<0.0001) is not significantly different from that expected if
actual turn size equalled the expected turn size.
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