Controlled expression of avian migratory fattening influences innate immune responses

While immunity is frequently suppressed when birds engage in strenuous migratory flights, whether and how immunity changes during the rapid accumulation of energy stores in preparation for migration remains largely unknown. Here, we induced pre-migratory fattening through controlled changes of daylight in common quails Coturnix coturnix and regularly assessed changes in a marker of constitutive innate immunity (Leukocyte Coping Capacity or LCC) and measures of body composition (lean and fat mass). LCC responses were highest in the mid-fattening phase and lowest when fattening was completed. At mid-fattening, we also found that the birds that kept a higher proportion of lean mass (i.e. accumulated less fat) had the highest LCC peaks. Our results indicate that migratory birds undergo rapid immunological changes as they accumulate energy stores for migration and propose that this could be due to competing or trade-off processes between metabolic remodelling and innate immune system function.