Over the last two and a half centuries, over a dozen species once found in the Midwestern United States have become extinct. Some of these animals, such as the passenger pigeon, were once so common that they would have been a common fixture on the landscape for generations of people living in this area. Other species were confined to very small ranges and occupied ecological niches which became impossible to hold once humans began to impact the land or water around them. Although ecological factors such as droughts undoubtedly had an impact on the populations of some of these animals, the primary causes of all these extinctions were generated by human activity, including overhunting or overfishing, logging, intentional culls of pests, introduction of non-native competitor species or pollution.