Analysis of the peregrine falcon's (Falco peregrinus) diet in Southern Sweden in relation to the current threat of avian influenza

Abstract

The peregrine falcon (Falco peregrinus) has recently recovered from the severe population decline in the 1970s where bioaccumulation of organochlorines caused thinning of their eggshells. In present times, highly pathogenic avian influenza (HPAI) has emerged as the current threat to peregrine populations. Monitoring in Sweden indicates a steady decline of breeding pairs since 2020 as the result of a major outbreak in wild birds. Species risk of being infected varies and therefore the peregrine's level of threat is uncertain depending on their diet composition. In this project, the diets of nesting peregrine falcons in southern Sweden have been examined and compared with data from 1983. This was done by reviewing images taken by camera traps between 2017-2024. The peregrine's risk of being infected by HPAI is discussed based on their diet. A size-dependent extrapolation was conducted to predict unknown prey. Results indicate that the peregrine falcon diet consists mainly of thrushes, gulls and corvids, doves and waders are slightly less common. Starlings and ducks are rare in their diet. Comparison between the performed prey estimate and 1970s display an increase in thrushes, small birds and corvids. Doves, gulls and starlings have decreased. The shift in diet can partly be confirmed by the Swedish Bird Survey. The risk of a peregrine falcon being infected by HPAI is quite indicative since gulls, which are highly affected, are a big part of their diet. Risks are thought to increase during winter, when migrating birds flock in western Europe and the range of prey changes. What causes such a big proportion of peregrines to be infected relative to other birds of prey remains untold and would be of great interest to investigate in further studies.