The impact of predation by birds on bat populations in the British Isles



The role played by predation of birds in the mortality of British bats is assessed. A review of dietary studies and anecdotal accounts revealed eleven species of bird which occasionally feed on bats–Herring Gull Larus argentatus, Black-headed Gull Larus ridibundus, Rook Corvus frugilegus, Carrion Crow Corvus corone, Little Owl Athene noctua, Short-eared Owl Asio flammeus, Kestrel Falco tinnunculus, Hobby Falco subbuteo, Merlin Falco columbarius, Peregrine Falco peregrinus and Sparrowhawk Accipiter nisus. A further three species feed more frequently on bats–Barn Owl Tyto alba, Tawny Owl Strix aluco and Long-eared Owl Asio otus. Rates of predation were very low accounting for only 00034oo of items taken by small hawks and falcons (n items = 29 519) but 0035o, of prey taken by owls (n items = 99 479). By multiplying together the average annual prey capture rates of the predators, assessed from their energetic food requirements and direct observations of prey intake rates, the British populations of the predators and the contribution to the diet made by bats, the annual number of bats which die each year as a result of predation was estimated. The total losses of bats to predation might amount to about 201 400 bats/annum. The most significant predators are Tawny Owl (c. 168 850 bats/annum), Barn Owl (c. 8800 bats/ annum), Long-eared Owl (c. 10 200 bats/annum) and Kestrels (c. 8400 bats/annum). This predation by avian predators would account for about 11 % of the annual mortality of British bats. An assessment of the biases involved in this calculation suggests it is probably a minimum estimate. Despite the apparent low representation of bats in the diets of predatory birds, the effects of this predation on bat behaviour and population dynamics cannot be ignored.