Non-foraging tool use in European Honey-buzzards: An experimental test

Examples of tool-use behaviors by birds outside foraging contexts are scarce and limited to a handful of species. We report a field experiment aimed to test whether an observed suite of odd behaviors by European Honey-buzzards (Pernis apivorus) represents use of green twigs cut from trees and woody shrubs as a tool to attract ants for anting. Specifically, we tested whether buzzards are selective in their choice of twigs, under the assumption that birds would prefer easy-to-collect twigs from plants that effectively attract ants. Experimental results lend support to our hypothesis that European Honey-buzzards cut green twigs of Montpellier maple trees (Acer monspessulanum) and, to a lesser extent, of Pyrenean oaks (Quercus pyrenaica) for their immediate use as ant attractors. Fresh twigs of both tree species attracted large numbers of ants, suggesting that their preferential use in the reported behavior of Honey-buzzards is not a random selection of the available plant material. Maple twigs, however, were the easiest to break and oak twigs the hardest compared to other plants in the community. This suggests that the relative ease of cracking of maple twigs may account for the preference Honey-buzzards have for this plant species as compared with Pyrenean oak, whose twigs demand considerable more effort from the birds to break. Our results lend support to the inclusion of the reported behavioral sequence by this raptor species as a potential example of tool use in birds outside the usual foraging context.