One of the more shocking statistics about the recent plight of birds is that it previously took on average some 500,000 years for one bird species to become extinct.
過去自然界只有遇到威力巨大的天災，才可能有大規模的環境變化，需要以萬年計的時間來調整，好恢復平衡的狀態。普通小規模的環境改變，進行很緩慢，以鳥類滅絕的速率而言，平均五十萬年才有一類鳥絕種。