Passenger Pigeon (Ectopistes migratorius): Estimated to have numbered three to five billion at the height of its population, it may have been the most numerous bird on Earth. Pigeon meat was commercialized as cheap food, resulting in hunting on a massive scale for many decades. There were several other factors contributing to the decline and subsequent extinction of the species, including shrinking of the large breeding populations necessary for preservation of the species and widespread deforestation which destroyed its habitat. Martha, thought to be the last passenger pigeon, died in 1914 at the Cincinnati Zoo. Eradication of the species has been described as one of the greatest and most senseless extinctions induced by humans.