Since no skull remains have been found, the diet of the animal is uncertain. Contrary to the giant terrestrial Cenozoic birds that lived in ecosystems without predators (or including only small carnivores), "Gargantuavis" cohabited with abelisaurids and dromaeosaurids theropods, so the place of this giant terrestrial bird in the Late Cretaceous ecosystems of the Ibero-Armorican island is unclear. "Gargantuavis" seems to have been an uncommon part of the fauna in its region. Despite numerous digs at sites where its bones have been found since its discovery, most have yielded only single specimens. Although its fossils are rare, the presence of "Gargantuavis" from southeastern France to north-western Spain shows that this bird had a wide distribution in the Ibero-Armorican island. It is possible that "Gargantuavis" lived mainly in an environment that was not compatible with fossilization, such as areas far from the rivers and floodplains, which represent most of the fossiliferous deposits in the late Campanian-early Maastrichtian of France and Spain.