Everglades National Park is home to one of eight remaining subspecies of Seaside Sparrow, the Cape Sable Seaside Sparrow (Ammodramus maritimus mirabilis), which is named for the southernmost point of land in the continental United States. Although the original range of this nonmigratory subspecies likely included all suitable freshwater and brackish water marsh habitats in south Florida, the current known distribution of this endangered sparrow is restricted to five separate subpopulations.
Changes in water distribution throughout the Everglades that resulted from repeated attempts to drain south Florida since the 1930s have caused a shift from freshwater vegetation to mangroves, bare mud flats, and salt-tolerant plants. In addition, the hurricane of 1935 is believed to have initiated dramatic changes in the plant community on Cape Sable from one dominated by freshwater plants to one dominated by salt-tolerant plants. A combination of sea-level rise, reduced freshwater flows to the area resulting from upstream water-management practices, and another hurricane in 1960 likely contributed to the habitat change. The area's hydroperiod (the length of time that water is present over the surface of a wetland) has been altered dramatically.