Greenfinches blood microbiome
In this study, we investigated the role that food availability played in shaping the body condition, blood microbiome composition, and overwinter survival rates of greenfinches (Chloris chloris). Our study coincided with a trichomonosis (caused by the Trichomonas gallinae parasite) epidemic that infected all individuals upon its outbreak, so the role of parasitic infection was also considered during analyses. Though all individuals were infected, those with irregular access to food tended to be able to better cope with this health detriment, as they had healthier body conditions, lower bacterial contamination in blood, and greater survival rates compared to birds with permanent food access. We had two periods of data collection: before the outbreak (in December), and after the outbreak (in February). Pre-epidemic measures for body condition (body mass, and fat and muscle scores) were uniform across birds and were not dependent on feeding regime. There was no observed bacterial contamination (relative abundance, and alpha and beta diversity) of the blood in either of the two groups pre-epidemic either. Following the outbreak, individuals with permanent access to food had lower body masses, lower fat scores, and lower muscle scores when compared to individuals with irregular access. Individuals with permanent access to food had higher relative abundances of bacterial microbes and tended to have higher alpha diversity when compared to individuals with irregular access. Beta diversity of blood microbes was not different between the two groups. We demonstrated the importance of feeding regime in mediating bird health during an outbreak, as body condition, blood microbial contamination, and survival rates were dependent on food accessibility. Our findings integrate feeding regime, coping response, and survival, to better understand and predict the complex interactions between diet, diseases, and physiological resilience in wild birds.  This research was supported by the Fundamental and Applied Research project No. lzp-2022/1-0348, funded by the Latvian Council of Science