Possibly the most significant avian ecosystem engineer might also be the least acknowledged. The passenger pigeon Ectopistes migratorius is sometimes presented as a superabundant species whose decline from billions during the 19th century to none by 1914 appeared to have no measured effects on its ecosystem [87]. However, passenger pigeons, which reached enormous densities in northern red oak Quercus rubra forests in North America, probably had substantial non-trophic effects by generating physical disturbance, tree breakage, increased fuel loads and higher fire frequency [88], as well as non-engineering effects via acorn consumption and nutrient deposition. Furthermore,after passenger pigeons went extinct, the oak crop increase might have augmented the populations of white-footed mouse Peromyscus leucopus and black-tailed deer Odocoileus hemionus, contributing to the higher frequency of Lyme disease currently observed [89]. Fascinating questions concerning ecosystem engineering by birds present an overlooked field of research in need of investigation by avian ecologists