Abstract
Between January 2017 and March 2018, Italy experienced a severe H5N8 Highly Pathogenic Avian Influenza epidemic, which was characterized by two waves: the first occurring from January to May 2017, and the second starting in July 2017. Interestingly, the second wave coincided with a period when migratory waterfowl were scarce or absent, indicating the potential involvement of resident wild bird populations. This led to the hypothesis that the virus might have amplified in nestlings and juvenile residential birds in the period between the two waves, and subsequently spread in July and August, when the juveniles left the natal areas following the moulting period.
A study was conducted between July 2019 and May 2021, to assess the extent of the movements of mallard ducks (Anas platyrhynchos) in their different phenological periods: breeding (May-June), moulting (July), post-moulting (August-October), and wintering/resting periods (between November and the following February). The study involved the placement of GPS-GSM transmitters on 73 mallards (37 males and 36 females) captured in two coastal and two inland wetlands, in proximity to the Densely Populated Poultry Areas in northeastern Italy. The GPS and satellite-derived data were used to assess the home ranges and land-use in the phenological periods. The results were then used to compute a measure of the probability of finding mallards within the maximum extent of their movements and, consequently, estimating the risk of contact with poultry farms.
The home ranges of mallards and their land-use patterns exhibited marked differences throughout the four periods and accordingly to sex and capture area. During the moulting period, movements resulted very limited, remaining confined within the wetlands of capture and their immediate vicinity. However, during the post-moulting and wintering periods, birds exhibited longer movements, especially those captured in inland wetlands. In the post-moulting/wintering periods the coastal wetlands showed frequent exchanges of birds, forming a territorial continuum. The coastal birds predominantly utilized natural wetlands, with occasional incursions into agricultural areas, while the inland mallards resulted more likely to visit agricultural settings and, to a much lesser extent, urban environments. The probability of encountering mallards was higher in the post-moulting and wintering periods, and for inland birds. For the coastal mallards, the highest presence of birds was confined within the wetlands, with minimal likelihood of encountering birds in the inland areas.
The study of mallard movements provided insights into their behaviour during different phases of their life cycle, highlighting variations in home range and land-use patterns. The measurement of the likelihood of finding mallards accordingly to the land-use might be used in developing risk-based surveillance plans for avian influenza in both wild birds and domestic poultry, aiming at focusing efforts in well-defined areas and temporal periods.