Figure 2
(a) We measured the effect of the manipulation at multiple angles. Birds and beetles are active during daylight hours. We therefore fixed the illumination at 65° that corresponds to the maximum elevation of the sun in mid-July at the site and time of collection (Ei). We then rotated the receiver in 5° increments from an elevation of Er = 20° (A) −160° (D) mimicking variable approaching directions of potential predators. The light grey lines indicate the spread of each of the receivers’ (Er) measurements. The receiver arm is not able to measure between geometries (B) and (C) due to the fixed illumination arm, hence there is a gap in the measurements between angles Er = 55°–75°. (b) The reflection properties of a structural surface (e.g. Oreina elytra) can be described as a diffuse cone of reflected light around the maximum reflection (λmax) of the surface19. After manipulation the directional properties of the surface could have either (A) stayed the same (B) changed in size, for example become more diffuse or (C) it could shift. (c) The predicted viewing geometry experienced by a bird during the experiments. The incident light (A) within the aviary is at an elevation of 65° in relation to the position of the beetle. After a bird landed on the barrier (B) it typically investigated the prey by moving approximately within the light grey arc (C) this creates a potential range of viewing geometries between 70°–100°. The viewing geometries change again if the bird approaches and/or attacks the beetle on or near the petri dish (D).
