|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
|
Fig. 1. Set-up for, and analysis of, dummy bird predation experiments. (A)
Experimental set-up. An experimental and a control female with their burrows
about 80 cm apart were separated by a barrier 20 cm high and 1.2–2.4 m
long, which prevented the control crab from seeing the bird dummy. The dummy
consisted of a 3 cm black styrofoam sphere that was moved directly over the
burrow of the test crab every 2–3 min, 20 cm above ground along a track
parallel or perpendicular to the barrier. The dummy was suspended from a
fishing line which ran through three pegs as shown in the diagram, thus
allowing an operator sitting about 4 m away to move it across the area. An
area of about 225–400 cm2 around each of the crabs' burrows
was continuously monitored by video throughout the activity period of the
crabs. (B) Data analysis. Individual frames were extracted from the video
sequences and images were histogram matched within and across days to one
standard image; subsequently, a region of interest was extracted in the blue
channel of the RGB image for pixel values larger than 200 (of 0–255
values in an 8-bit image). The pixels captured in this procedure are shown in
red in the bottom right image. For further details see Materials and
methods.
|
