The topic of my PhD is how climate change affects species interactions. In particular, I am interested in how species with vastly different annual cycles (resident and migrant birds) that are sympatric and have a similar niche during the breeding season may differ in their phenological adjustments to climate change. Adjustments are (at least partially) thought to be driven by a shift in the temperature regulated timing of the caterpillar peak, the main food resource of many passerines during reproduction. My model species are the resident great tit Parus major and the long distance migrant pied flycatcher Ficedula hypoleuca. These species occur in roughly similar frequencies in our breeding populations, and P. major breeds on average 2 weeks earlier than F. hypoleuca. Their reproductive timing may adjust at different rates or through different mechanisms (phenotypic plasticity for residents versus micro-evolution for long distance migrants), potentially changing their phenological overlap. To study the consequences of more or less phenological overlap between these species, I experimentally adjust the reproductive timing (advance/control/delay) of P. major to create plots with more and less overlap with F. hypoleuca. I measure the prey choice and reproductive success of both species. I expect that more phenological overlap between species will lead to niche differentiation and have negative fitness consequences. The implications are that climate change may not only put pressure on long distant migrant pied flycatchers by shifting their main food resources, but also by enhancing competition with resident species.