Apple Snails and Snail Kites

By Jenn Bernatis, Ph.D.

Changes in Florida’s freshwater ecosystems over the decades have had a myriad of impacts on native species. Now, we are looking at the possibility of relying on an invasive snail, Pomacea maculata, to support the federally listed Snail Kite (Rostrhamus sociabilis plumbeus). Snail Kites feed almost exclusively on Apple Snails, but population declines in the native Florida Apple Snail (Pomacea paludosa) appear to be occurring in traditional kite nesting areas. Over the last 12 years, the invasive P. maculata (Island Apple Snail) has spread throughout the state becoming an alternate food source in many systems where Snail Kites nest. Many of these nesting sites are manipulated for a variety of reasons, yet definitive impacts on the snails and birds remains uncertain.

East Lake Tohopekaliga is a nesting site for Snail Kites and home to both the Florida Apple Snail and Island Apple Snail. The lake is slated for an extensive restoration including draw-down, scraping and removal of sediment, and vegetation treatments. This system has provided state and federal researchers with the opportunity to monitor both snail and bird activity pre-restoration, during restoration, and post-restoration. The data collected during this period will provide much-needed data that can be used in determining future restoration activities at sites with Apple Snails.

At this time four sampling events, two summer and two winter, have been conducted. These sampling events use a combination of throw traps, transects, wading, snorkeling, and scuba diving to locate snails. More than 800 sites have been sampled around the lake ranging from 0.25 m to 2.25 m deep. More than half of the snails collected have been in depths greater than 0.75 m. The majority of the sites with snails have some sort of vegetation, either emergent or submersed, but a few snails have been collected at sites with no vegetation. More snails have been collected in the summer, as this is also peak reproductive period than in the winter. This finding demonstrates conclusively that snails utilize deeper water and that Apple Snail surveys need to focus on a range of depths and not just the shallow marsh areas.

Tracking the snails long term will provide information critical to dealing with Apple Snail populations. Although invasive Apple Snails are economically and potentially ecologically damaging, they are serving a critical role as a food source for the Snail Kite. Understanding the movement patterns and use of the water column by Apple Snails will allow managers to better anticipate the impacts on Snail Kites and adjust management plans accordingly. Likewise, the research will provide information that may be of use in developing snail eradication programs. Previous tactics have included draw-downs in an attempt to kill the snails through desiccation. This is not an applicable approach as it is known that invasive Apple Snails can survive out of the water for at least a year. The question that will be answered is, “Are the snails burying?” which they are capable of, or “Are the snails following the water?” at which point the draw-down will have minimal impacts on Apple Snails. If the snails bury, and scraping is part of the proposed activity, then reintroducing the Apple Snails, preferably the native, may need to be considered in locations with Snail Kite nesting history. Ultimately, this study will fill in missing data gaps on snail ecology and provide necessary information when working with systems with Apple Snails and particularly those with Snail Kites.