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 ..., , Version 1 has the unit associated with the variable 'handling' as hours, but it is in minutes. Version 2 is updated correctly.