# Predator–Prey Dynamics Between Eurasian Sparrowhawk and Its Bird Prey During Spring Migration in the Forests at Hel Peninsula (N Poland) over 1982–2024

## TL;DR

This study examines how the migration timing of the Eurasian Sparrowhawk relates to its prey during spring in northern Poland, considering the effects of climate change.

## Contribution

The study reveals sex-specific migration patterns in Sparrowhawks and their adaptive timing in relation to prey availability under climate change.

## Key findings

- Adult Sparrowhawks migrate two to three weeks earlier than youngs, with young females migrating 10 days ahead of young males.
- Migration timing of adult females correlates with large prey like Blackbirds, while adult males correlate with smaller prey like Robins.
- Sparrowhawks adjust their migration timing each spring to prey availability, but their overall phenology has not shifted over time.

## Abstract

We investigated how the spring migration timing of the Eurasian Sparrowhawk is related to the timing of its five main bird prey species, considering climate change in Europe, which should affect both prey and the predator. Using bird ringing data (26 March–15 May, 1982–2021) at a stopover site Hel (N Poland), we found that adult Sparrowhawks migrated on average two to three weeks ahead of youngs. Young females, which can mate with older males, migrated 10 days ahead of young males. Adults occurred at Hel early following a warm February–March at wintering grounds in southern Europe. Migration timing of female Sparrowhawks (the larger sex) was related to that of large prey: Blackbird (adults) and Song Thrush (youngs). Adult males’ timing was related to Robins (small birds); young males showed no such relationships, but they migrated later, when all prey species were available. Robins and Song Thrush shifted spring passage by a few days over 1982–2021, but not Sparrowhawks. We suggest that Sparrowhawks (generalist predators) adjust migration timing each spring to some prey, but their phenology has not shifted, as they hunt various species. Understanding predator–prey dynamics in forests is important in the face of climate change.

Climate change in Europe can influence the predator–prey interactions, a scarcely studied topic in birds. We examined relationships between the spring passage timing of the Eurasian Sparrowhawk, a generalist peak predator, and its main bird prey species (Song Thrush, Eurasian Blackbird, Common Chaffinch, Great Tit, European Robin). All species were ringed daily (26 March–15 May) in 1982–2021 at Hel Peninsula (N Poland). In 2024, we collected pluckings to identify Sparrowhawks’ prey. Sparrowhawks’ daily migration dynamics and those for the Song Thrush, Robin and Chaffinch were correlated. Sparrowhawks’ median dates of passage showed no multi-year trend, but large variation, correlated with those of its prey and with temperatures. Adult females and males migrated through Hel early after warm February and March at wintering grounds. Young males migrated early during warm Aprils at Hel. Medians were correlated between adult males and Robins, adult females and Blackbirds, and young females and Song Thrush. This suggests that Sparrowhawks adjust their migration timing each spring to the availability of these three prey species, with some sex differences, as males are smaller than females. Identifying changes in predator–prey dynamics in response to climate change helps us understand its effect on forest ecosystems.