3) Dusky Seaside Sparrow
Chemicals and human oversight were to blame for the demise of the dusky seaside sparrow. In an effort to curtail mosquito populations within Florida's Merritt Island salt marshes, DDT was sprayed over the area, contaminating the sparrow's food chain and causing a severe shrinkage in their numbers. The situation grew exponentially worse in the '60s when the marshes around Kennedy Space Center were flooded to remove mosquito breeding grounds, inadvertently destroying those of the sparrows. Following highway construction soon after, the species was officially declared extinct in 1990.