Migration distance does not predict blood parasitism in a migratory songbird

Abstract

Migration can influence host–parasite dynamics in animals by increasing exposure to parasites, by reducing the energy available for immune defense, or by culling of infected individuals. These mechanisms have been demonstrated in several comparative analyses; however, few studies have investigated whether conspecific variation in migration distance may also be related to infection risk. Here, we ask whether autumn migration distance, inferred from stable hydrogen isotope analysis of summer‐grown feathers ( δ 2 H f ) in Europe, correlates with blood parasite prevalence and intensity of infection for willow warblers ( Phylloscopus trochilus ) wintering in Zambia. We also investigated whether infection was correlated with individual condition (assessed via corticosterone, scaled mass index, and feather quality). We found that 43% of birds were infected with Haemoproteus palloris (lineage WW1). Using generalized linear models, we found no relationship between migration distance and either Haemoproteus infection prevalence or intensity. There was spatial variation in breeding ground origins of infected versus noninfected birds, with infected birds originating from more northern sites than noninfected birds, but this difference translated into only slightly longer estimated migration distances (~214 km) for infected birds. We found no relationship between body condition indices and Haemoproteus infection prevalence or intensity. Our results do not support any of the proposed mechanisms for migration effects on host–parasite dynamics and cautiously suggest that other factors may be more important for determining individual susceptibility to disease in migratory bird species.

Highly Pathogenic Avian Influenza A(H5N8) Virus in Swans, China, 2020

“…Soon after, similar viruses were reported in southern central Russia in late July 2020, and they jumped into wild birds in September in Russia and Kazakhstan (Appendix Table 1). Migratory birds moving within several flyways in Eurasia have overlapping breeding areas ( 8 ), and breeding origin assignments suggest that migration distances vary by a maximum of ≈3,500 km ( 9 ). Such a unique ecosystem could be implicated as a pathway for the cross-regional spread of HPAI viruses during the autumn migration of waterfowl.…”

Nowhere to escape: the cross‐age avian haemosporidian exposure of migrants in northeast China

“…Therefore, the second scenario is more likely to occur in our case, i.e. adults of migratory species are less influenced by parasites in resident species in their breeding areas, and the parasites detected in yellowrumped flycatcher adults were acquired in wintering areas (Sorensen et al 2019, Soares et al 2020 or along the flyway (Valkiūnas 2004, Krauss et al 2010.…”

“…To date, studies on the effect of bird migration have focused mainly on adult infection dynamics (Ramey et al 2012, Hellgren et al 2013, Neto et al 2015, Pulgarín‐R et al 2019, Sorensen et al 2019), while nestlings attracted much less attention. However, life‐history theory predicts that the variation in resource acquisition or the manner in which it is allocated at one life stage has downstream effects on fitness (Stearns 1992, Lindström 1999, Metcalfe and Monaghan 2001), and, in the case of migration, future reproductive success is an applicable offset to the costs of infection in that process (Stearns 1976, Alerstam et al 2003).…”

Animal migrations and parasitism: reciprocal effects within a unified framework

“…and Leucocytozoon spp.) are not associated with any detectable cost based on various measures related to migration success, ranging from fat reserves prior to departure, white blood cell counts or body condition during migration, to arrival time or return rates to breeding grounds (Ashford, 1971; Davidar & Morton, 1993; Rätti, Dufva & Alatalo, 1993; Cornelius, Davis & Altizer, 2014; Hahn et al ., 2018; Sorensen et al ., 2016, 2019). By contrast, a few other studies report that haemosporidian infections are associated with lower fat reserves during migration, longer stopover duration, reduced body mass at arrival, and/or delayed arrival at the breeding grounds in passerines (Møller, de Lope & Saino, 2004; Garvin, Szell & Moore, 2006; Emmenegger et al ., 2018 b ; Hegemann et al ., 2018; Ágh et al ., 2019), raptors (Ishak et al ., 2010), and waterfowl (Merrill et al ., 2018).…”