Modelling avian visual detection of prey species

Research in the past 30 years has established that birds are tetrachromatic, with an SWS1 opsin sensitive to either violet (VS) or ultraviolet (UVS) wavelengths. Much work has been done to investigate the existence of UV signals in avian plumage and their potential role in mate choice, but less has been done on the role the SWS1 opsin plays in detecting prey. To investigate this, I am using objective multispectral (Visible + UV) photography and cone-catch modelling to investigate perceived brightness and chromatic contrast of potential animal prey items (frogs and lizards) against a variety of natural backgrounds, as perceived by the avian visual system. I can also compare the differences in perception between VS and UVS models. I find that in general crypsis tends to extend into the UV. VS and UVS models generally differ in perceived contrast by very little, indicating that the shift in sensitivity of the SWS1 opsin is not driven by prey color. Some lizards have tails which reflect brightly in the UV, contrasting their body and the background. This may be an adaptation for visual deflection, attracting the avian predator’s gaze to the detachable and non-vital tail. Individual lizards can change their luminance (brightness) as perceived by the avian double cone (dbl) by 300-1000 percent. Contrasting patterns of high and low UV reflectance are common in the aposematic signals of poison frogs.