Great Blue Heron is North America's largest wading bird. While fish make up most of their diet, they will also eat frogs, insects, mice and other small animals. Like many birds during the 1800s, their numbers were greatly reduced due to killing for the millinery trade. Their populations have rebounded and the International Union for Conservation of Nature and Natural Resources Red List lists them as a species of Least Concern. However, populations of the “Great White Heron” subspecies in southern Florida has declined possible due to elevated mercury levels in local waterways.