Abstract
Abstract Immune response to pathogens such as avian malaria (Plasmodium spp.) and related haemosporidian parasites (Haemoproteus spp. and Leucocytozoon spp.) can lead to increases in energy demands of birds. Migrations are energetically costly for birds and require resources that could be otherwise invested in immune defence against pathogens. Here, we examined the prevalence and intensity of haemosporidian parasites (Apicomplexa, Haemosporida) in rosy starlings (Pastor roseus), an irruptive migrant on the Balkans, during their pre-migratory period. We further evaluated if these infections affected the stress levels of birds brought into overnight captivity, using leukocyte profiles (ratios of heterophils to lymphocytes, or H/L ratios). Haemosporidian parasites were detected based on microscopic examination, PCR and sequencing. We found high prevalence of haemosporidian parasites (83.9%) in rosy starlings (n=31), with predominant infections of Haemoproteus pastoris (cytochrome b lineage LAMPUR01) (80.1%). All birds had high heterophil/lymphocyte ratios (mean = 3.86), indicating the transition to captivity was stressful. However, there was no added stress from blood parasite infection during captivity, since infected birds did not have significantly higher heterophil/lymphocyte ratios than uninfected birds, despite all birds facing the same stress conditions. There was a negative correlation between intensity of H. pastoris and monocyte proportions, which may indicate an association with infection, or an artefact of the stress-induced shift in leukocyte profile following captivity. Our findings suggest that blood parasites have minimal additional impact on rosy starlings during an acute stress scenario (overnight captivity), arguing that they carry little cost to the energetically challenging migratory flight.
Highlights
Migratory birds are exposed to multiple and various pathogen agents during their journeys that could challenge their immune system [1]
We further evaluated if these infections affected the stress levels of birds brought into overnight captivity, using leukocyte profiles
In the 31 rosy starlings examined for haemosporidian parasites we found high overall prevalence (83.9% of the genera Haemoproteus and Plasmodium)
Summary
Migratory birds are exposed to multiple and various pathogen agents during their journeys that could challenge their immune system [1]. Avian malaria and related haemosporidian parasites (Apicomplexa, Haemosporida) are widespread and taxonomically diverse blood parasites that can have numerous impacts on their hosts [5, 6]. These pathogens need blood-feeding vectors (Diptera) to maintain transmission among potential avian hosts [7]. Recent evidence suggests that avian haemosporidian parasites can negatively influence breeding success [9, 10], moulting [11], fat accumulation [12] and importantly, optimal migration of the infected birds [13]
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