New Study of Eurasian Eagle Owl Diet Reveals Threatened Giant Bush-Crickets

Scientists examining the Eurasian Eagle Owl diet in Bulgaria earned a fresh insight on the often overlooked and rare bush-crickets, better understanding the distribution and possibly conservation of this insect species.

Led by Dr. Dragan Chobanov from the Institute of Biodiversity and Ecosystem Research and Dr. Boyan Milchev from the University of Forestry, both in Bulgaria, the study reports the increased presence of Big-Bellied Glandular Bush-Cricket (Bradyporus macrogaster) in the diet of Eurasian Eagle Owls. The insect has been threatened with extinction, and this discovery strongly suggests that its predator could help identify locations still rich in biodiversity and subsequently need protection. Details of their findings are published in the open-access and peer-reviewed journal Travaux du Muséum National d'Histoire Naturelle "Grigore Antipa."

An Input for Updating Biodiversity Conditions in the Balkans

The Balkan Peninsula - where the Republic of Bulgaria is located - has been recognized globally as the location with the greatest diversity of orthopterans - an order of insects that include grasshoppers, locusts, crickets, and bush-crickets - in Europe. This is especially true in the middle of the European region, along the Vardar and Struma rivers' valleys. However, it has also been identified as the location for a significant number of threatened species.

Additionally, a thorough and updated assessment of the orthopterans' conservation status in Bulgaria is currently insufficient. Most studies regarding insects, on orthopterans, in Bulgaria are focused on faunistic characteristics (geographical distribution) and taxonomy of species. This condition prompted the researchers to conduct a study regarding the condition of these insects - going through dietary information from the pellet dropping of Eurasian Eagle Owls. The study covers 53 breeding sites located in the southeastern part of Bulgaria.

Bush-Crickets: A Staple Part of Bird Diet in the Balkans

As a result, scientists were able to identify three different species of bush crickets that have been included as an integral part of the diet of Eurasian Eagle Owl. Furthermore, all three discovered species of the orthopterans are all reported as rare or threatened in the Balkan nation.

Among these staple dietary insects is the Big-Bellied Glandular Bush-Cricket, marking a special case since this particular species is already threatened by extinction.

The local decline in mammals and birds weighing 0.2 and 1.9 kilograms - the range of preferred prey for the Eurasian Eagle Owl - led the opportunistic predator to hunt larger insects for its sustenance. Additionally, researchers raise the possibility of other overlooked species that have become prey for the owl species.

Scientists are now using this new distribution data to prompt the designation of a new Natura 2000 site - with the new site being a part of an interconnected network of protected areas for Europe's valuable and threatened species and habitats. The new proposal takes into account the newly-discovered interconnected interferences of conservation problems, plus the supposed vulnerability of the Big-Bellied Glandulat Bush-Cricket.

Also, the concerned species require habitats with low disturbance and high vegetation diversity. This, plus the bird's large size and easy location through the species singing males, researchers noted that the proposed location is a suitable bioindicator for the species' community health.