Exposing migratory sparrows to Plasmodium suggests costs of resistance, not necessarily of infection itself

Abstract

Migratory birds move through multiple habitats and encounter a diverse suite of parasites. This raises concern over migrants' role in transporting infectious disease between breeding and wintering grounds, and along migratory flyways. Trade-offs between flight and immune defenses could interfere with infected individuals' migratory timing and success, potentially affecting infection dynamics. However, experimental evidence that parasitic infection affects migratory preparation or timing remains scant. We hypothesized that birds encountering hematozoan parasites shortly before migration incur physical costs (reduced body condition) and behavioral costs (delayed migration), due to the infection itself and/or to the demands of mounting an immune response. We experimentally inoculated song sparrows (Melospiza melodia) with Plasmodium shortly before fall migration. We monitored infection and body composition for 2 weeks after inoculation, and used radiotelemetry to track timing of migratory departure for another 7 weeks after release. Inoculated individuals that resisted infection had lower lean mass 12 days post exposure, relative to controls and infected individuals. This suggests trade-offs between body composition and immune defenses that might reduce migration success of resistant individuals. Despite group differences in body composition prior to release, we did not detect significant differences in timing of migration departure several weeks later. Thus, malarial infection did not appear to incur detectable costs to body composition or to migratory timing, at least when exposure occurs several weeks before migration. This study is novel considering not only the costs of infection, but also the costs of resisting infection, in an experimental context.

Migratory behaviour does not alter cophylogenetic congruence between avian hosts and their haemosporidian parasites

“…Similarly, even though migrants can disperse haemosporidians (de Angeli Dutra et al ., 2021 b ), these migratory species may contribute only to parasite dispersal if host species in their new community are phylogenetically similar to their original migratory host. In addition, haemosporidians do not necessarily reduce avian migration success, or do so negligibly (Hahn et al ., 2018 ; Kelly et al ., 2018 ; Ágh et al ., 2019 ). When they do, only birds presenting high parasitaemia or in the acute phase of infection might be unable to complete their migration (Altizer et al ., 2011 ; Poulin and de Angeli Dutra, 2021 ).…”

Uropygial gland microbiota differ between free-living and captive songbirds

“…This staggered collection method allowed us to sample free-living and captive birds at approximately the same time of year across years (August 2017, July 2018), thus reducing the likelihood that sampling would be influenced by seasonal effects. All birds were sampled in the post-breeding period (determined by lack of brood patch and/or cloacal protuberance and based on knowledge of typical breeding and migration dates for this species 34 , 73 ), thereby reducing the likelihood that sampling would be influenced by behavioral, hormonal, or other physiological effects associated with breeding. In migratory song sparrows, moult initiation dates are variable but usually occur between mid-June to mid-September 34 , so we do not think individual differences in moult status are likely to have affected our results.…”