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

Abstract

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. RESUMEN. Ataques de aves passeriformes en bandadas de especies mixtas por parte del gavilan euroasi atico (Accipiter nisus): estrategias de los depredadores y presas potenciales La depredaci on es un factor esencial que afecta a las poblaciones de las presas, pero los ataques son notoriamente dif ıciles de observar en tiempo real. Aqu ı presentamos datos descriptivos sobre el comportamiento de ataque de los gavilanes euroasi aticos (Accipiter nisus) y las t acticas de escape de sus presas en los bosques de con ıferas de Letonia durante la epoca no reproductiva. En un per ıodo de 36 años (1985-2020), observamos 199 ataques de gavilanes euroasi aticos a bandadas de especies mixtas de pequeños paseriformes de bosque, 19 ataques tuvieron exito (9,6%). Los gavilanes atacaron principalmente desde arriba del dosel de las con ıferas maduras o desde justo debajo de las ramas inferiores del dosel. Los ataques de los gavilanes tuvieron m as exito en el dosel inferior (N = 17) que en el superior (N = 2). Catorce de los 19 individuos de aves paseriformes muertas por los gavilanes pertenecieron a Regulus regulus, Poecile montanus y Periparus ater, las aves de tamaños pequeños com unmente est an limitadas al dosel inferior por especies m as grandes y dominantes que ocupan el dosel superior. Los ataques del gavil an a las aves situadas en el dosel superior rara vez tuvieron exito, probablemente porque las aves paseriformes del dosel superior est an m as ocultas por la vegetaci on y es m as probable que detecten a los depredadores que se acercan. Nuestros resultados sugieren que la s...

Female common cuckoo calls dampen the mobbing intensity of great reed warbler hosts

“…Moreover, the female cuckoo calls had the same effect as sparrowhawk calls had on the attentiveness of wintering great tits ( Parus major ) and blue tits ( Cyanistes caeruleus ) outside the breeding season, two species that are only seldom parasitised by the cuckoo (Grim et al., 2014). Tits constitutes an important part of the sparrowhawk's diet during winter (Krams et al., 2020; Newton, 1986), when the cuckoos are on their sub‐Saharan wintering grounds (Bán et al., 2018).…”

Animal Movement Strategies

“…We parameterised our visibility index calculations based on the hunting flight altitude of a raptor that commonly preys on small birds, the Eurasian sparrowhawk (Accipiter nisus). Sparrowhawks and other bird-preying raptors hunt by surprising their prey via low-level flight, as hovering or high-flying raptors are conspicuous and can be easily detected (Krams 2001;Krams et al 2020). In line with experimental and observational work, we assumed an observer height of 1.5m above surfaces (tree canopy, fields, or other) (Seress et al 2011;Krams et al 2020), and an observer visual range of 50m.…”

“…Sparrowhawks and other bird-preying raptors hunt by surprising their prey via low-level flight, as hovering or high-flying raptors are conspicuous and can be easily detected (Krams 2001;Krams et al 2020). In line with experimental and observational work, we assumed an observer height of 1.5m above surfaces (tree canopy, fields, or other) (Seress et al 2011;Krams et al 2020), and an observer visual range of 50m. We used the 'Visibility Analysis' plugin v1.2 for QGIS v3.20 to calculate visibility scores over the study area (Cuckovic 2016).…”

“…In biological terms, the visibility index is an estimate of how exposed any location is to a low-flying aerial predator, up to 50 m away. We modelled these values based on the hunting flights of a common bird-preying raptor, the Eurasian sparrowhawk (Accipiter nisus Krams 2001;Seress et al 2011;Krams et al 2020). We also considered the visibility index of our study site from the point of view of a typically high-flying raptor, the common kestrel (Falco tinnunculus), and repeated the visibility index calculations for an observer height of 15m (Fig.…”

“…Cross-species studies of movement and habitat selection in molting birds could benefit from dramatic advances in the high-throughput position tracking of small species (Toledo et al 2020;. Birds, among other animals, can take the spatial perspective of visual predators, and avoid risky, exposed areas in favour of sheltered ones (Hampton 1994;Emery 2000;Krams 2001;Davidson and Clayton 2016;Krams et al 2020). Shelter is often only proxied by correlated variables, such as vegetation growth (Pettorelli et al 2011).…”