Agonistic tool use? A Northern Cardinal (Cardinalis cardinalis) uses pebbles to strike its reflection

Abstract

Tool use has been observed in over two dozen families of birds, though few wild birds outside of corvids have been observed using tools in acts of agonism; we present additional accounts of this behavior in both corvids and cardinals. On 9 June 2023 we observed and video-recorded a male Northern Cardinal (Cardinalis cardinalis) repeatedly pick up a pebble and strike the side-view mirror of a vehicle in a parking lot at Great Smoky Mountains National Park, Tennessee, USA. We searched YouTube and found several videos of wild birds attacking their reflection in a mirror or window. None appeared to use a pebble or other weapon to attack, but a White-winged Chough (Corcorax melanorhamphos) used a pebble to strike the windshield of a vehicle and a Common Raven (Corvus corvax) dropped a stone on a domestic dog. We interpret our observation as indicating tool use by a Northern Cardinal, one of the few accounts outside of corvids of a bird using a tool in an act of agonism. We also show that online videos can help researchers detect novel behaviors, including tool use and tooling, in wild birds.