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.