A mimicked bacterial infection prolongs stopover duration in songbirds—but more pronounced in short‐ than long‐distance migrants

Abstract

Migration usually consists of intermittent travel and stopovers, the latter being crucially important for individuals to recover and refuel to successfully complete migration. Quantifying how sickness behaviours influence stopovers is crucial for our understanding of migration ecology and how diseases spread. However, little is known about infections in songbirds, which constitute the majority of avian migrants. We experimentally immune-challenged autumn migrating passerines (both short- and long-distance migrating species) with a simulated bacterial infection. Using an automated radiotelemetry system in the stopover area, we subsequently quantified stopover duration, "bush-level" activity patterns (0.1-30 m) and landscape movements (30-6,000 m). We show that compared to controls, immune-challenged birds prolonged their stopover duration by on average 1.2 days in long-distance and 2.9 days in short-distance migrants, respectively (100%-126% longer than controls, respectively). During the prolonged stopover, the immune-challenged birds kept a high "bush-level" activity (which was unexpected) but reduced their local movements, independent of migration strategy. Baseline immune function, but not blood parasite infections prior to the immune challenge, had a prolonging effect on stopover duration, particularly in long-distance migrants. We conclude that a mimicked bacterial infection does not cause lethargy, per se, but restricts landscape movements and prolongs stopover duration, and that this behavioural response also depends on the status of baseline immune function and migration strategy. This adds a new level to the understanding of how acute inflammation affect migration behaviour and hence the ecology and evolution of migration. Accounting for these effects of bacterial infections will also enable us to fine-tune and apply optimal migration theory. Finally, it will help us predicting how migrating animals may respond to increased pathogen pressure caused by global change.

Immune function and blood parasite infections impact stopover ecology in passerine birds

“…viruses, bacteria), we can, however, not exclude that additional co-infections may contribute to the observed effects. In any case, free-flying birds undergoing infections might not only prolong stopover duration (Hegemann et al 2018 , this study), but pathological sickness symptoms may also reduce their flight range. Interestingly, birds infected with blood parasites showed significantly longer landscape movements (i.e., movements away from the catching site) than uninfected birds and there was a trend that this effect increased from single to double infections.…”

“…First, in passerine birds, haptoglobin concentrations in the range of 1.0–2.0 mg/ml or even higher regularly occur (Hegemann et al 2012a ; Vermeulen et al 2016 ; Ndithia et al 2017 ; Fowler and Williams 2017 ). Second, haptoglobin concentrations increase during inflammation (Thomas 2000 ; Buehler et al 2009 ; Matson et al 2012 ; Hegemann et al 2013a ; but see Schultz et al 2017 ) and third, a recent study has shown that birds prolong their stopover duration during an experimentally induced inflammatory response (Hegemann et al 2018 ). That we had only one bird in our dataset with very high haptoglobin values is not surprising, because this is a marker of an on-going acute inflammation.…”

“…Infections are known to hamper migration performance in a variety of taxa, including mammals (Mysterud et al 2016), insects (Bradley and Altizer 2005), fish (Sjöberg et al 2009) and birds (Risely et al 2018) and we recently demonstrated that an energetically costly mimicked bacterial infection increases stopover duration in songbirds (Hegemann et al 2018). However, there is no study investigating to what extent mild and/or chronic parasite infections impact stopover ecology in songbirds, which constitute the vast majority of avian migrants.…”

A physiological perspective on the ecology and evolution of partial migration

“…Hegemann et al (2015) hypothesised that individuals which are sick or parasitized need to invest into an acute immune response. Such a response includes a range of energetically, physiologically and behaviourally costly adjustments (Lee et al 2005;Owen-Ashley et al 2006;Owen-Ashley and Wingfield 2007;Hegemann et al 2012bHegemann et al , 2013aHegemann et al , 2018Sköld-Chiriac et al 2015). Consequently, infected individuals might not be able to afford a demanding migration and hence have to become resident.…”

Recovery from infection is more likely to favour the evolution of migration than social escape from infection

“…Thus, parasite dispersal and/or the accumulation of new infections along migratory routes is typically seen as a consequence of migratory behaviour rather than parasites themselves acting as drivers of host migration decisions (Altizer, Bartel, & Han, 2011). Yet, theoretical and empirical evidence that parasites influence the migratory decisions of their hosts is increasing (Daversa, Fenton, Dell, Garner, & Manica, 2017; Daversa, Manica, Bosch, Jolles, & Garner, 2018; Halttunen et al, 2018; Hegemann et al, 2018; Shaw & Binning, 2016; Shaw, Craft, Zuk, & Binning, 2019b). Predicting how infection may influence host migration requires not only accounting for changing infection risk, but also being explicit about the mechanism linking infection and migration—infection could be predicted to either increase or decrease host migration depending on the circumstance (Binning, Shaw, & Roche, 2017).…”