Animal migration is a major driver of infectious agent dispersal. Duck and seabirds migrations, for instance, play a key role in the spatial transmission dynamics and gene flows of avian influenza viruses (AIV), worldwide. On tropical islands, brown and lesser noddies (Anous stolidusandA. tenuirostris) may be important AIV hosts, but the lack of knowledge on their migratory behaviour limits our understanding of virus circulation in island networks. Here we show that high connectivity between islands generated by post-breeding behaviours could be a major driver in the spread and the maintenance of AIV among tropical islands. Tracking data highlight two types of behaviours during the non-breeding season: birds either staying in the vicinity of their breeding ground (on Bird Island, Seychelles), or moving to and roosting on other islands in the Indian Ocean. Differences in roosting places are detected between migrant birds, ranging from the Tanzanian coast to the Maldives archipelago and Tromelin Island. Epidemiological data further support that brown and lesser noddies are major hosts for AIV, although significant variation of seroprevalence between species suggest that other drivers are involved in virus infection and transmission dynamics.

We investigated coronavirus circulation in three tern species, in four islands of the Western Indian Ocean (Bird, Reunion, Europa, Juan de Nova). None of the 1513 samples tested positive by RT-PCR. We discuss the implication in term of host species range, ecological drivers of virus transmission, and diagnostic tools.