Once found throughout Florida, this bird now calls Duval & Nassau counties home

The marsh wren's range in Florida has shrunk by 80 percent from its historical extent

St. Johns River is the southern edge of the MacGillivray’s seaside sparrow’s range that has contracted from marshes further south in Florida, through New Smyrna Beach and is widely accepted to have disappeared. (wjxt)

JACKSONVILLE, Fla. – A tiny bird that once ranged across much of Florida is now only found around the St. Johns River in Duval and in Nassau counties due to increasing human development.

The marsh wren’s range in Florida has contracted by 80 percent from its historical extent.

The birds’ favored home is along edges of the river and tidal creeks within the salt marsh dominated by tall and short forms of smooth cord grass.

The marsh wren’s range contraction, small population size and restricted distribution led to the species being listed as threatened in the state.

Scientists looked at possible reasons why the birds have undergone range contractions and found several factors working against the species.

Researchers looked for Marsh Wren nests at five sites on the Nassau River and Clapboard Creek in Duval and Nassau counties in 2016 and 2017 and found troubling issues.

Overall habitat loss in salt marshes are resulting from pressures such as river dredging, shoreline hardening along with the most substantial threat coming from greater than normal high tides.

Survey points sampled for Worthington’s Marsh Wrens and MacGillivray’s Seaside Sparrows during 2014 and 2015 breeding seasons. Dotted line on main map and shaded counties in inset map represent historical ranges; solid line represents both 2000‐2001 and current ranges.

Sea-level rise from climate change has increased the high tide flooding into nesting sites, increasing the rate of nest failure for MacGillivray seaside sparrows.

Tidal flooding confines predators in breeding areas, making the flooding issue even worse.

The effect of tide height on nest survival suggests that salt marsh birds in northeast Florida are vulnerable to continued sea-level rise, which is exacerbated by upland development that will hinder marsh migration.

Scientists say monitoring and protecting northeast Florida’s high-elevation, cord grass marshes should be a priority in helping to sustain the bird populations.

About the Author:

After covering the weather from every corner of Florida and doing marine research in the Gulf, Mark Collins settled in Jacksonville to forecast weather for The First Coast.