Data from: Immune challenge reduces daily activity period in free-living birds for three weeks

Non-lethal infections are common in free-living animals and the associated
sickness behaviours can impact crucial life-history trade-offs. However,
little is known about the duration and extent of such sickness behaviours
in free-living animals, and consequently how this affects life-history
decisions. Here, free-living Eurasian blackbirds Turdus merula were
immune-challenged with lipopolysaccharide (LPS) to mimic a bacterial
infection, and their behaviour was monitored for up to 48 days using
accelerometers. As expected, immune-challenged birds were less active than
controls within the first 24 hours. Unexpectedly, this reduced activity
remained detectable for 20 days, before both groups returned to similar
activity levels. Furthermore, activity was positively correlated with a
pre-experimental index of complement activity, but only in
immune-challenged birds, suggesting that sickness behaviors are modulated
by constitutive immune function. Differences in daily activity levels
stemmed from immune-challenged birds resting earlier at dusk than control
birds, while activity levels between groups were similar during core
daytime hours. Overall, activity was reduced by 19% in immune-challenged
birds and they were on average almost 1 hour less active per day for 20
days. This unexpected longevity in sickness behaviour may have severe
implications during energy-intense annual-cycle stages (e.g., breeding,
migration, winter). Thus, our data help to understand the consequences of
non-lethal infections on free-living animals.