Avian ultraviolet vision and frequency-dependent seed preferences

It is well established that ultraviolet sensitivity plays an important role in the visually guided behaviour of birds. From a foraging perspective, ev idence now exists that ultraviolet wavelengths are used by birds when forag ing for insects, berries, seeds and mammals. Here, we present the results o f two laboratory experiments that test the effect of removing (i) ultraviol et wavelengths and (ii) wavebands in the human-visible region on the freque ncy-dependent seed preferences of zebra finches (Taeniopygia guttata). Alth ough the seeds and backgrounds used in our experiments reflected mainly at long wavelengths, we found that removal of ultraviolet wavelengths signific antly changed the strength and direction of frequency dependence compared w ith full-spectrum illumination. We also found that the removal of ultraviol et wavelengths (300-400 nm) did not affect the strength of frequency depend ence compared with the removal of short wavelengths (approximately 400-500 nm), medium wavelengths (approximately 500-600 nm) or long wavelengths (app roximately 600-700 nm). Since frequency-dependent selection has direct cons equences for the stability of prey populations and the spectral quality of ambient light is known to vary considerably with climate, time of day and l ocal habitat geometry, our results suggest that ultraviolet wavelengths mig ht play an important role in the dynamics of plant populations. However, we urge caution about overestimating the importance of ultraviolet wavelength s compared with wavelengths in the human-visible spectrum.