Conclusions
We found that diet macronutrient content can alter the abundance of some bacterial taxa in the gut and potentially alter the relationships between gut microbial communities and physiological responses important for responding to infection. Additionally, we found that immune-challenged birds alter feeding behavior by selectively reducing protein but not fat intake, however this change in feeding behavior did not correspond with detectable differences in gut microbiota communities. Contrary to our predictions, heightened infection risk (being housed near immune-challenged conspecifics) did not alter feeding behavior, gut microbiota, or immune and endocrine physiology. However, regardless of treatment, higher fat consumption in these individuals was associated with lower gut microbial richness and diversity. Our findings carry implications for host health and epidemiology, as diet-induced shifts in the microbiome and physiology could shape disease transmission dynamics through nutritionally driven shifts in host-pathogen interactions. Future work should explore if reduced protein consumption during infection is adaptive for hosts in terms of responding to and overcoming infection, as this could have implications for disease transmission.