A new study in Bulgaria has shown that Eurasian Eagle-Owls are eating bush-crickets following the decline of preferred small bird and mammal prey.
The researchers found a frequent presence of the threatened Big-bellied Glandular Bush-Cricket (Bradyporus macrogaster) in the diet of Eurasian Eagle-Owls, and concluded that the bird could be used to identify biodiversity-rich areas in need of protection. The study was conducted in south-eastern Bulgaria and published in Travaux.
While the Balkan Peninsula has already been recognised as the area with the highest diversity of Orthoptera (grasshoppers, crickets and bush-crickets) in Europe and one of the generally most biologically diverse areas in the whole Palearctic realm, it is also home to a worrying number of threatened species.
Additionally, a thorough and updated country assessment of the conservation status of the Orthoptera found in Bulgaria is currently lacking. This is why the Bulgarian team undertook a study on the biodiversity of these insects by analysing food remains from pellets of Eurasian Eagle-Owls, collected from 53 breeding sites.
As a result, the scientists reported three species of bush-crickets that have become a significant part of the diet of the birds. Curiously enough, all three species are rare or threatened in Bulgaria. The case of the Big-bellied Glandular Bush-Cricket is of special concern, as it is a species threatened by extinction. Meanwhile, the local decline in mammals and birds that weigh between 0.2 and 1.9 kg, which are the preferred prey for Eurasian Eagle-Owls, has led the highly opportunistic predator to increasingly seek large insects for food.
Given the vulnerability of the Big-bellied Glandular Bush-Cricket, a species with a crucial role in the food chain, the scientists call for the newly provided data to prompt the designation of a new Natura 2000 site. Additionally, due to the species' requirements for habitats of low disturbance and high vegetation diversity, and its large size and easy location via singing males, they point out that it makes a suitable indicator for habitat quality and high biodiversity.
Chobanov, D & Milchev, B. 2020. Orthopterans (Insecta: Orthoptera) of conservation value in the Eurasian Eagle Owl Bubo bubo food in Bulgaria. Travaux du Muséum National d’Histoire Naturelle 63(2): 161-167. DOI: 10.3897/travaux.63.e53867