Figure 2.

Fluorescence characteristics of the budgerigar M. undulatus (a–d) and the stomatopod crustacean L. glabriuscula (e–i). (a,b) White light and UV fluorescent excitation photographs of front and back of head showing fluorescent cheek and crown feathers. Excitation source was a ‘black light’. Shaded box indicates spectral zone removed by sunblock to remove fluorescence. (c) Normalized reflectance—lines colour-coded to approximately match bird; fluorescent crown feathers—light yellow, lower cheek, non-fluorescent yellow feathers—dark yellow (note difference in UV absorption of fluorescent feathers, which absorb in this wavelength range to re-emit as fluorescence), blue cheek patches—blue (note high UV reflectivity of these feathers and high chromatic contrast to yellow fluorescent feathers). UV ‘black-light’ excitation source used in (b)—solid black line, fluorescent excitation spectrum—long-dashed line, fluorescent emission—short-dashed line. (d) Spectral sensitivities—solid black lines, spectral emission difference (relative photons) between fluorescent feathers with and without sunblock applied—yellow line. (e,f) Frontal aggressive display in white light and blue-light excited fluorescence. (g) L. glabriuscula looking out from burrow in sand under fluorescent excitation. Fluorescent areas on antennal scales are conspicuous. (h) Fluorescent excitation spectrum—long-dashed line, fluorescent emission—short-dashed line. Spectral sensitivity of the row 2 distal photoreceptor in stomatopod retina showing excellent match to fluorescent emission range. (i) Ambient light in ocean at around 10 m in stomatopod habitat—blue line, fluorescent excitation lamp relative output—purple line and yellow blocking filter—yellow line. These were used in photography of stomatopods and match both natural ambient light and long–waveband-pass retinal filter of stomatopod (cryosection—natural colour—of filter inset photograph).