Seasonal plasticity and energy efficiency in migratory buntings is an assemblage of alterations in metabolic and gut microbe adaptations.

Circulatory system is the source of useful metabolites to enable organismal energy demands of muscle during different life states of birds including migration. In this study, we profiled the serum metabolites and fecal microbiome of redheaded buntings (Emberiza bruniceps) exhibiting diurnal non-migratory (nonM) pre-migratory (preM), migratory (M) and post-migratory (posM) states, when exposed to long days (14L:10D). Using gas chromatography, out of the identified 124 serum analytes, 38 showed significant variations (Fold change, VIP) between states. Out of these, 11 metabolites (short chain fatty acids, SCFAs-butanoate and hexanoate, lactate, pyruvate, ethylene and acetate oxime, pyridoxal phosphate (PLP), niacin, L-valine and carboximidic acids viz. phosphatidyl ethanolamine (PE) and diethyl carbamate) involved in energy pathways and enhanced immunity showed higher abundance in M state. While, upsurge of L-valine suggested energy contribution of glucogenic branched chain amino acids (BCAAs) in M state, that of leucine metabolite, was related to higher temperature in posM birds. Gut microbiota was analysed using faeces of buntings (n=6 each) during nonM and M states and alteration in bacterial compositions was observed; faeces of nonM birds were enriched in proteobacteria, while those of M were rich in firmicutes. This study reports the migratory state specific changes in the serum metabolome and faecal microbiome of the buntings and highlights the role of short chain fatty acids, SCFAs and branched chain amino acids, BCAAs during hypermetabolic state of migration.