Avian gut microbiome, timing of breeding and fitness consequences

Climate change poses threats to wild animal populations, e.g., through phenological mismatches that affect prey availability and abundance. The type and abundance of prey consumed determine birds' diet, which is one of the main factors shaping the gut microbiome. A healthy gut microbiota helps the host with food digestion, absorption of nutrients and detoxification. It also impacts processes such as immune responses or protection against pathogens. This in turn may affect birds' fitness and population dynamics.
Since captivity alters the composition of microbial communities it is important to investigate them in natural conditions. In birds, gut microbiota develops after hatching, but remains subject to environmental factors. Therefore, current
conservation efforts should account for the impact of environmental factors on avian gut microbiota and, ultimately, animal fitness.
I will fill these research gaps by testing the following hypotheses:
i) The composition of the gut microbiota in birds is affected by the diet, which in turn is affected by seasonal change.
ii) Environmental factors, including diet, are more important factors than genetics.
iii) The avian gut microbiome is associated with the host's fitness.