A direct test of the impact of infection on animal migration: consequences for parasite and host populations

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Wildlife populations experience a wide range of infections that can both impact on their own health and cross species boundaries to pose environmental risks to farm animal and human health. The impact of this infection will be inextricably linked to a species' movement ecology, as the way in which animal movements around their environment is a major factor in determining how infections are transmitted and persist. Predicting infection dynamics and mitigating their impacts therefore requires understanding how infection influences animal movements and, in turn, understanding the consequences of animal movement for infection dynamics. We will therefore address three key questions in this project: 1) Does infection status influence individual migration strategy? 2) Does infection affect the survival and breeding success of migrants and residents to different extents? 3) Do differences in migratory behaviour scale up to affect levels of infection in host populations.We will investigate these questions in a partially migratory population of seabirds that breed on the Isle of May National Nature Reserve in South East Scotland but migrate along the East Coats of the UK. Recent theoretical studies have modelled three disease related mechanisms that could directly affect selection for, or against, migration. These are 1) migratory escape, whereby migration allows individuals to escape from high-exposure habitats or infected individuals. 2) migratory recovery, whereby infected individuals migrate to a different area to gain resources that facilitate recovery 3) migratory culling, whereby infected individuals suffer higher mortality during migration.We will firstly test whether natural levels of parasitism are associated with individual migration strategy expressed in an individual's first year of life and whether measures of immunity differ in juveniles that subsequently become resident or migrant. We will then experimentally test whether parasitism has a causal role through experimental reduction of parasite burden.We will then test whether parasitism is associated with differences in breeding success and survival of migrants and residents. We will use multi-year demographic data to link individual migration strategy to levels of parasitism and components of fitness to test a) whether parasitism is associated with any potential selective advantage of migration and b) the demographic routes through which this may operate.Finally we will test whether changes in population levels of parasitism between years is due to decreases in individual parasite burden as individuals recover from infection or the loss of infected hosts from the population as they fail to survive. This is important from a management or conservation point of view as these alternative explanations would lead to very different conclusions about the robustness of the population to infection.This study will therefore provide first combined test of how parasitism drives migratory movements in a partially migratory species with measuring the consequences for population level changes in parasite abundance and whether these result from high levels of host mortality. These are key to assessing the impact of migration on parasite persistence in the environment and the impact of parasitism on different components of animal populations.