Diet specialisation during brood rearing has important consequences on parental reproductive success and on the recruitment rate of offspring. However, very little is known about the long-term consistency of parents when feeding their offspring. Here, we used Mediterranean Great Tits Parus major to test the hypothesis that parents show a consistent level of individual specialisation across years. To do this, we recorded prey delivered to 10-14 day-old chicks over six years. We standardised the data to control for environmental factors and used a Principal Component Analysis (PCA) to characterise the foraging provisioning behaviour of individuals. We assessed long-term dietary consistency using data from individuals recorded in two different years by performing a repeatability analysis (absolute consistency) and also running a Generalised Linear Mixed Model, where we measured the consistency of position of individuals in a group, relative to others (relative consistency). The PCA analysis showed that diet selection when provisioning chicks varies across two gradients: prey size vs. frequency of prey delivery, and caterpillars vs. spiders. Controlling for these factors, we found that both individual repeatability and the correlation of diet choices between years were moderately significant. Although Great Tits show high individual dietary specialisation within a year, diet fluctuates to some extent across years. This could provide a degree of flexibility to parents dealing with highly fluctuating environmental conditions as well as a buffer against climate change, and could be a consequence of increasing lifetime experience.
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