Abstract
Avian malaria parasites (Haemosporida, Plasmodium) are of cosmopolitan distribution, and they have a significant impact on vertebrate host fitness. Experimental studies show that high parasitemia often develops during primary malaria infections. However, field studies only occasionally reveal high parasitemia in free-living birds sampled using the traditional methods of mist-netting or trapping, and light chronic infections predominate. The reason for this discrepancy between field observation and experimental data remains insufficiently understood. Since mist-netting is a passive capture method, two main parameters determine its success in sampling infected birds in wildlife, i. e. the presence of parasitized birds at a study site and their mobility. In other words, the trapping probability depends on the survival rate of birds and their locomotor activity during infection. Here we test (1) the mortality rate of wild birds infected with Plasmodium relictum (the lineage pSGS1), (2) the changes in their behaviour during presence of an aerial predator, and (3) the changes in their locomotor activity at the stage of high primary parasitemia.We show that some behavioural features which might affect a bird's survival during a predator attack (time of reaction, speed of flush flight and take off angle) did not change significantly during primary infection. However, the locomotor activity of infected birds was almost halved compared to control (non-infected) birds during the peak of parasitemia. We report (1) the markedly reduced mobility and (2) the 20% mortality rate caused by P. relictum and conclude that these factors are responsible for the underrepresentation of birds in mist nets and traps during the stage of high primary parasitemia in wildlife. This study indicates that the widespread parasite, P. relictum (pSGS1) influences the behaviour of birds during primary parasitemia. Experimental studies combined with field observations are needed to better understand the mechanisms of pathogenicity of avian malaria parasites and their influence on bird populations.
Highlights
The evidence for parasite impacts on their hosts has been reported in various host-parasite associations [1]
The majority of cited studies or case reports have shown that avian haemosporidian parasites can be dangerous for non-adapted bird species like, for example, penguins [24] or endemic Hawaiian honeycreepers of the Drepaniidae [9] that did not co-evolve with these parasites, and in bird species, which have been evolutionarily exposed to these infections for long periods, for example, the blackbird Turdus merula in Europe [15]
As an indication of parasite prevalence in the community: in all, 753 trapped birds were infected with haemosporidians (Haemoproteus spp., Leucocytozoon spp.), and 76 of them were infected with Plasmodium spp
Summary
The evidence for parasite impacts on their hosts has been reported in various host-parasite associations [1]. Based on limited available experimental data and scarce case reports from wildlife, it is difficult to estimate how many individuals from certain populations get malaria infections, how many of them survive, and what are the behavioural changes in the parasitized birds. This information is crucial for determining factors that are important for the survival of infected birds in nature. Answering these questions would contribute to the better understanding of host-parasite interactions and epidemiology of avian malaria in wildlife
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