The dusky seaside sparrow was a non-migratory subspecies of the seaside sparrow that became extinct in 1987. It was found in South Florida, along the St. John's River and in the marshes of Merritt Island.
In order to control the mosquito population in the areas next to the Kennedy Space Center, Merritt Island was flooded and the sparrows' nesting grounds were compromised, causing a decline in their numbers. A few years later, the marshes along the St. John's River were drained to facilitate highway construction, and the sparrows' numbers were further reduced. According to the U.S. Fish and Wildlife Service, the last known dusky seaside sparrow died on June 17, 1987.