How much would egg and duckling predation need to be reduced to reverse declines of ground-nesting waterfowl in Finland? A demographic scenario analysis

Abstract Populations of water- and wetland-associated birds have declined globally due to multiple pressures, including habitat loss, climate change, and predation. Ground-nesting waterfowl are particularly vulnerable to predators, and the spread of invasive mammalian predators like raccoon dogs ( Nyctereutes procyonoides ) has intensified this threat in parts of Northern Europe. Predator removal has previously been implemented to support waterfowl populations, with mixed outcomes across studies. Here, we used a demographic state-space model within a Bayesian framework to evaluate the population-level consequences of hypothetical reductions in predation for three duck species that have shown population declines in Finland: Eurasian wigeon ( Mareca penelope ), Eurasian teal ( Anas crecca ), and tufted duck ( Aythya fuligula ). Using long-term pair-index data (1986–2024) from Southern and Central Finland together with literature-based demographic parameters, we estimated average egg-to-fledging survival conditional on the assumed values of the remaining demographic parameters. We then conducted scenario-based simulations in which egg and duckling predation was reduced and evaluated the resulting changes in population growth. Under the tested demographic assumptions, the reduction in egg-to-fledging predation estimated to be sufficient to reverse population declines ranged from 3.3 % to 18.1 % across species and scenarios. Under the most optimistic demographic assumptions, a 5.7 % reduction was estimated to be sufficient to yield population growth for all species and regions studied. The magnitude of the required reduction depended on assumptions about post-fledging survival and the division between predation and natural mortality. Our modelling framework provides a quantitative basis for examining how changes in predation pressure may translate into population responses under current demographic uncertainty.