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

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.

Impact summary

Our work will achieve two key aspects of economic and societal impact:
1) It will help to guide policy decisions by several key stakeholder organisations.
2) It will facilitate educational and public understanding of science activities.

Firstly, we have identified, and engaged with, several key stakeholders that could potentially make direct use of both the data we will generate and the conclusions we will draw to inform policy decisions. This includes Scottish Natural Heritage (SNH) and Natural England (NE) who are statutory advisors to the UK Government in relation to the natural environment and the Centre for Expertise on Animal Disease Outbreaks (EPIC) who interface with government departments to advise on epidemiology, population health and disease control in relation to animal health. SNH and EN are required to offer advice to Government on activities such as establishing Marine Protected Areas, on all proposals for marine renewable energy in UK Territorial Waters. They have identified the value of the spatial component of our proposed data collection as this will assist with making informed planning decisions. Our work is conducted in an area of international conservation importance, is designated as an SPA it is recognised as a key habitat for a range of internationally important species. Our study area is the focus of several marine planning developments including the extension of marine protected areas and our colleagues are frequently asked to offer advice to the renewable energy sector on proposed developments. The spatial data we will collect is directly relevant to these proposals.

A further novel part of this current proposal is that we will also link movement data to infection status of birds that migrate to different areas. This both adds resolution to the importance of key sites and expands the potential to examine key routes of disease transmission between the marine and terrestrial environment. For example, the nematode parasites we study can cause illness when consumed in under-cooked fish and incidences of infection have increased with popularity of eating raw food and sushi. Our study species is a marine forager but is tied to land for key activities and is a host of generalist pathogens of economic importance. EPIC has therefore identified our data as being relevant to colleagues who are modelling how movement of overlapping wild animal populations may relate to observed patterns of infection in farming and aquaculture.

Education and the wider community
There is considerable widespread interest in both natural environment and the different species that inhabit it. Our study site on the Isle of May is a National Nature Reserve with over 10,000 visitors a year and the opportunity to view it's wildlife via webcams at other sites of interest and online. These are regularly accessed have encouraged many interested parties to become involved in our research via citizen science schemes. We also have well established links with local schools where we have provided input to practical activities within the curriculum for excellence module ecology and the environment. Our proposed impact activities will extend this work in primary education to provide web resources that both entertain and inform schoolchildren about opportunities to become directly involved in learning about the value of our natural environment.