Milk bottles revisited: social learning and individual variation in the blue tit, Cyanistes caeruleus

Blue tits are famous for the ‘milk bottle’ innovation, which emerged at numerous sites across Britain in the early 20th century. However, overall we still know little about the factors that foster or hinder the spread of innovations, or of the impact of individual differences in behaviour on social transmission. We used a two-action and control experimental design to study the diffusion of innovation in groups of wild-caught blue tits, and found strong evidence that individuals can use social learning to acquire novel foraging skills. We then measured six individual characteristics, including innovative problem solving, to investigate potential correlates of individual social-learning tendency. Consistent with a hypothesis of common mechanisms underlying both processes, we found evidence for a relationship between social learning and innovativeness. In addition, we observed significant age- and sex-biased social learning, with juvenile females twice as likely to acquire the novel skill as other birds. Social learning was also more likely in subordinate males than dominant males. Our results identify individual variation and transmission biases that have potential implications for the diffusion of innovations in natural populations.