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Sanibel Island Rice Rat research status

By Staff | Apr 22, 2020
PHOTO PROVIDED Sanibel Island Rice Rat
PHOTO PROVIDED One of 12 bucket camera traps the Sanibel Island Rice Rat team uses.
PHOTO PROVIDED Black rat
PHOTO PROVIDED Cotton rats

The Sanibel Island Rice Rat (SIRR) is an “at-risk” mammal occurring in semi-aquatic and coastal marshes, hydric hammocks, mangrove swamps, and freshwater marshes and meadows only on Sanibel. Individuals most often forage and nest in salt marsh communities or along the ecotone between marsh-mangrove or marsh-buttonwood uplands. Historically, conservation land managers monitored rice rats on their properties biannually using transects and small-mammal traps (i.e. Sherman traps). In 2019, the University of Florida completed a four-year refuge-funded effort which included more intensive, systematic trapping and habitat assessments. Preliminary results from the study indicate that the SIRR populations are declining, and that almost 100 percent of the cordgrass grids studied in the past are now of poor quality due to hardwood encroachment.

Encroachment of upland vegetation into the freshwater marshes known to support the SIRR is believed to be a major threat to recovery of the small mammal. Sand cordgrass is the historically dominant species in SIRR habitat, and typical areas were open, grassy, and lacked any tree canopy due to natural factors like wind, salt spray, salinity, fire, changes in water table, and periodic inundation from tropical storms and hurricanes. Unfortunately, an altered fire regime and changes in water management have reduced the dominance of sand cordgrass in rice rat habitat. Shrubby native species like wax myrtle and buttonwood, as well as invasive plants like Brazilian pepper and cogongrass, now occur throughout much of the marshes. The increasing dominance of these shrubby and non-native species is believed to be reducing foraging habitat and potential nesting substrate for the SIRR, and may increase perching sites for aerial predators such as hawks and owls.

In the fall, the U.S. Fish and Wildlife Service’s Partners for Fish and Wildlife Program partnered with the city of Sanibel and Sanibel-Captiva Conservation Foundation to fund a Sanibel Island Rice Rat Habitat Restoration Project on lands adjacent to the J.N. “Ding” Darling National Wildlife Refuge. The project location is a mosaic of FWS-, city- and SCCF-owned parcels, and has documented occurrence of SIRR. Initial mechanical removal of trees and shrubs was planned to begin in April, so preliminary SIRR monitoring began in February. Twelve bucket camera traps were placed within the planned project area to monitor presence and absence of SIRR. Photos collected in late March showed use by black rats, but no use by SIRR.

Although vegetation management work has been postponed due to the current COVID-19 pandemic, camera work will continue through the spring. Additionally, camera work will be conducted intermittently during treatment and post-treatment phases to monitor SIRR response to activities and treatments. The refuge, city and SCCF are planning follow-up prescribed burning in the treated areas between 2021 and 2023 to reduce new shrub encroachment and promote growth of sand cordgrass and other wetland grasses

Erin Myers is deputy refuge manager at the J.N. “Ding” Darling National Wildlife Refuge.