Avian influenza represents one of the greatest concerns for public and animal health that has emerged from the animal reservoir in recent times. Avian influenza is a pathogen of the type A influenza virus which is adapted to avian hosts. These viruses most commonly infect wild bird species and poultry, and are also known to infect a variety of mammals, including humans. In principal low pathogenic avian influenza (LPAI) viruses cause only mild diseases. In contrast to the LPAI subtypes H5 and H7, who can become highly pathogenic (HPAI) after introduction into poultry which may cause disease outbreaks (?bird flu? or ?fowl plague?). Birds of wetlands and aquatic environments, particularly species of Anseriformes (ducks, swans, geese) and Charadriiformes (gulls, terns, waders) are considered to be the major natural LPAI virus reservoir. Within the order of Anseriformes and Charadriiformes, dabbling ducks of the Anas genus, and in particular Mallards (Anas platyrhynchos), are found to be infected more frequently with a LPAI virus. The research project aims to study the interactive ecology of Mallards with a LPAI virus in a natural setting, by providing critical knowledge on: (1) who is the vector for the LPAI virus: residents or migrants, (2) which individuals are more susceptible for infection with a LPAI virus, (3) when do individuals become infected with a LPAI virus, and (4) what is the impact of a LPAI virus infection on the reproduction of a host.