The strategy to survive primary malaria infection: An experimental study on behavioural changes in parasitized birds

Malaria
is caused by protozoan parasites of the genus Plasmodium. Avian malaria parasites are prevalent worldwide, and
they infect the great majority of terrestrial bird species. Malaria is thought
to have reduced the populations or even caused the extinction of some endemic
bird species in Hawaii. However, fitness effects of the parasite on mainland
birds are still poorly understood. Also it is unclear whether we get a full
picture about the numbers of diseased wild birds using the method of mistnetting.

Here,
we evaluate experimentally the behavioural changes of siskins caused by a malaria
parasite during predator attack, and evaluate the impact of disease on birds’
activity. These parameters are important in nature for survival. We found that
infected birds do not differ in their reaction to aerial predators until they
are on terminal stage but markedly reduced their mobility during primary
infection. Together with mortality caused by infection, these factors are
responsible for the considerable underrepresentation of infected birds in mist
nets and traps in wildlife projects.

Underestimation
of parasite burden might mislead our understanding of the true pathogenicity
and disease epidemiology in wildlife. These results should be recognized in
studies addressing parasite virulence and demography of birds, particularly
when estimating mortality rates in wildlife populations.