Continuous low-intensity predation by owls (Strix aluco) on bats (Nyctalus lasiopterus) in Spain and the potential effect on bat colony stability

Abstract

Owls prey on bats, but information on owl predation is scarce, its impact on bat mortality is unclear, and reports on behavioural responses, including roost-switching and fission–fusion behaviour, are equivocal. To study the link between owl predation and anti-predator behaviour in bats, we evaluated seven months of video recordings at roosts and the behaviour of 51 passive integrated transponder (PIT)-tagged bats and bats without tags in a geographically isolated colony of greater noctule bats ( Nyctalus lasiopterus ) in Spain. We found the tawny owl Strix aluco to almost continuously hunt N. lasiopterus , from perches and on the wing, well after the bats emerged at dusk and when they returned to their roosts. We recorded 39 unsuccessful and three successful attacks. Nonetheless, we found no evidence that owl predation modifies bat behaviour. While the bats constituted only a very small proportion of the owls' diet, owl predation accounted for an estimated 30–40% of bat mortality, which may have a significant impact on small, local or isolated bat populations, in particular, and thereby shape regional bat distributions. We hypothesize that low roost availability may also affect the bats’ potential response to predation, which could lead to natural predation having an excessive impact on bat populations.

Dangerous neighbours: Birds and bird‐eating bats sharing tree cavities

“…In some cases, this competition has resulted in the killing of bats, leading to adverse demographic consequences for the latter (Hernández‐Brito et al., 2014 , 2018 ). Greater noctules are also preyed upon by avian predators, particularly tawny owls ( Strix aluco ), whose predatory pressure has been found to exert negative effects on the stability of bat colonies (Kelm et al., 2023 ). In all such cases, the birds involved typically have a much larger size than the bats.…”

Improving the science and practice of using artificial roosts for bats

“…Artificial roost use could elevate predation risk for bats if such roosts are conspicuous, easily accessed by predators, and used on roost‐limited landscapes. Because artificial roosts are often conspicuous (e.g., placed on buildings, poles, or along forest edges [Mering & Chambers, 2014]), these structures could become targets for repeated predation attempts when bats are at roost or when they emerge (Kelm et al., 2023). In Norway, soprano pipistrelles ( Pipistrellus pygmaeus ) are repeatedly depredated by corvids and gulls while roosting and emerging from building‐mounted boxes; corvids even developed novel strategies for dislodging bats from boxes, but no predation attempts were documented at nearby woodland roosts during an 11‐year study (Michaelsen et al., 2014).…”