Attacks of songbirds in mixed-species flocks by Eurasian Sparrowhawks: strategies of predators and potential prey

Predation is an essential factor affecting prey populations, yet attacks are notoriously difficult to observe in real time. Here, we provide descriptive data about the attack behavior of Eurasian Sparrowhawks (Accipiter nisus) and the escape tactics of their prey in coniferous forests in Latvia during the non-breeding season. Over a period of 36 years (1985–2020), we observed 199 attacks of Eurasian Sparrowhawks on mixed-species flocks of small forest passerines, with 19 attacks being successful (9.6%). Sparrowhawks attacked mainly from either above the canopy of mature conifers or just below the lower branches of the canopy. Attacks by sparrowhawks were more successful in the lower canopy (N = 17) than the upper canopy (N = 2). Fourteen of the 19 songbirds killed by sparrowhawks were Goldcrests (Regulus regulus), Willow Tits (Poecile montanus), and Coal Tits (Periparus ater), small songbirds typically limited to the lower canopy by larger, more dominant species that occupy the upper canopy. Sparrowhawk attacks on birds located in the upper canopy were rarely successful, likely because songbirds in the upper canopy are more concealed by the vegetation and more likely to detect approaching predators. Our results suggest that the spatial segregation of members of mixed-species groups of wintering songbirds can be explained by their responses to microhabitat (canopy height) gradients in predator exposure that are enforced by group dominance hierarchies.