A hidden cost of migration? Innate immune function versus antioxidant defense

Migration is energetically demanding and physiologically challenging. Migrating birds, for example, need to boost their antioxidant defenses to defeat the pro-oxidants produced during high energetic activity. The enhanced antioxidant defense possibly withdraws limited resources (e.g. energy or micronutrients) from other physiological functions, such as immune defense. Such a trade-off might not occur outside the migration seasons or in resident individuals. Here, we investigate if there is a negative relationship between innate immune function and antioxidant defense by sampling both migrating and resident blackbirds (Turdus merula) at the same location during the same period of the annual cycle. We show that in migrating blackbirds microbial killing capacity (BKA), an integrative measure of baseline innate immune function, was negatively correlated with total non-enzymatic antioxidant capacity. In contrast, in resident conspecifics, sampled at the same time and location, these two phys...