Wildlife conservation has faced a string of challenges over the past 150 years. Overhunting led to the extinction of the passenger pigeon and nearly the bison. Hunting seasons and bag limits did an excellent job of addressing over-consumption problems. Habitat destruction became an issue as wetlands were drained and forests cleared – an issue which helped encourage the development of our national wildlife refuge and national forest systems, yet remains an important issue today. Then contaminants fouled our water and air, leading to the Clean Water and Clean Air Acts and the control of pesticides. Today, in addition to those challenges we are faced with new issues like invasive species and climate change.