ULTRAVIOLET CUES AFFECT THE FORAGING BEHAVIOR OF BLUE TITS

The function of avian ultraviolet (UV) vision is only just beginning t o be understood. One plausible hypothesis is that UV vision enhances t he foraging ability of birds. To test this, we carried out behavioural experiments using wild-caught blue tits foraging for cabbage moth and winter moth caterpillars on natural and artificial backgrounds. The l ight environment in our experiments was manipulated using either UV-bl ocking or UV-transmitting filters. We found that the blue tits tended to find the first prey item (out of four) more quickly when UV cues we re present. This suggests that UV vision offers benefits to birds when searching for cryptic prey despite the prey and backgrounds reflectin g relatively little UV Although there was no direct effect of UV on th e time taken to find all four prey items in a trial, search performanc e in the absence of UV wavelengths tended to increase over the course of an experiment. This may reflect changes in the search tactics of th e birds. To our knowledge, these are the first data to suggest that bi rds use UV cues to detect cryptic insect prey and have implications fo r our understanding of protective coloration.