Host Plant and Habitat Measurements
Background color, texture, complexity, and lighting can impact the
perception of visual signals (Endler 1993). To account for the influence
of background on artificial prey detection and/or perception, I measured
two main habitat characteristics: canopy openness and plant size. I
anticipated that more open canopies would increase avian attack rates
(Blake & Hoppes 1986; Richards & Coley 2008), possibly by providing
better lighting conditions for prey detection. In terms of plant size, I
expected that individual prey items would be easier to find on smaller
plants, also increasing avian attacks. Plant height measurements were
taken (in cm) from ground-level at the base of the stem to the tip of
the uppermost leaf. Plants used in the experiment were an average of
124.9cm tall (sd: 60.1cm). I measured canopy openness by taking upward
digital photos with a 180° hemispheric lens at plant height directly
above each plant, with the camera held level with the ground. I then
processed these photos using ImageJ (version 1.53) to calculate the
proportion of open sky relative to vegetative cover in each image.