The microbial community in the gut is influenced by environmental factors, especially diet, which can moderate host behaviour through the microbiome-gut-brain axis. However, the ecological relevance of microbiome-mediated behavioural plasticity in wild animals is unknown. We presented wild-caught great tits (Parus major) with a problem-solving task and showed that performance was weakly associated with variation in the gut microbiome. We then manipulated the gut microbiome by feeding birds one of two diets that differed in their relative levels of fat, protein and fibre content: an insect diet (low content), or a seed diet (high content). Microbial communities were less diverse among individuals given the insect compared to those on the seed diet. Individuals were less likely to problem-solve after being given the insect diet, and the same microbiota metrics that were altered as a consequence of diet were also those that correlated with variation in problem solving performance. Although the effect on problem-solving behaviour could have been caused by motivational or nutritional differences between our treatments, our results nevertheless raise the possibility that dietary induced changes in the gut microbiota could be an important mechanism underlying individual behavioural plasticity in wild populations.

肠道中的微生物群落受到环境因素（尤其是饮食）的影响，这些因素可以通过微生物组-肠脑轴调节宿主行为。然而，在野生动物中微生物组介导的行为可塑性的生态相关性是未知的。我们展示了野生大山雀（Parus major）与解决问题的任务，并表明性能与肠道微生物组的变化之间存在弱关联。然后，我们通过喂食鸟类脂肪，蛋白质和纤维含量相对水平不同的两种饮食之一来控制肠道微生物组：昆虫饮食（低含量）或种子饮食（高含量）。与种子饮食相比，给予昆虫的个体中的微生物群落差异较小。给予昆虫饮食后，个体解决问题的可能性较小，并且由于饮食而改变的相同微生物群指标也与解决问题性能变化相关。尽管对解决问题行为的影响可能是由于我们的治疗之间的动机或营养差异造成的，