Data from: 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
physiological measures were not correlated. This suggests that migrating
birds trade off innate immune function and antioxidant defense.
Furthermore, and likely a consequence of this trade-off, in migrant
blackbirds BKA was positively correlated with oxidative damage to lipids.
In resident blackbirds BKA and degree of lipid oxidation were
uncorrelated. The mechanism and currencies of the supposed trade-off are
currently unknown, but energetic investments or micronutrients are likely
candidates. Future experimental studies could provide more conclusive
evidence for this trade-off; yet, our results open up a new level of
thinking about the physiological costs of migration.