Crows break off live camphor twigs: an avian disturbance effect on plants

Abstract

Birds are usually considered beneficial partners for plants, acting as predators on herbivorous insects, pollinators and seed dispersal agents. However, in an urban area of central Japan, birds break off large quantities of live camphor tree (Cinnamomum camphora) twigs in winter. This loss of vegetative parts was examined quantitatively to estimate the impact on the trees. I also observed bird foraging behaviour to determine the species involved and the possible reasons underlying this destructive activity. Broken twigs on the forest floor were found to have numerous leaves and spring buds. The densities of leaves and buds in the litter were 288.5 and 54.4 m(-2), respectively. The jungle crow (Corvus macrorhynchos) may have broken off the twigs either to peck the fruits while perching on stable branches, or possibly to remove twigs obstructing access to fruit. In contrast, brown-eared bulbuls (Hypsipetes amaurotis), oriental turtle doves (Streptopelia orientalis) and rove doves (Columba livia) ate fruits without breaking twigs. The interaction between C. camphora and C. macrorhynchos only extends back for about 20 years in urban Japan, indicating that this is unlikely to be a stable, co-evolved relationship.