Amphibians (frogs, toads, and salamanders) are good indicators of environmental changes. They are closely tied to both land and aquatic habitats and are sensitive to factors such as pollution, drought, habitat loss, and disease. In the rapidly urbanizing region around Washington, DC, the potential for multiple and interacting stressors is significant. These factors may cause changes in amphibian distribution, numbers, and the diversity of species at a given site (species richness). They may also cause increases in diseases and malformations.
Amphibians play an important role in the food web, serving as prey for many fish, reptile, bird, and mammal species and in turn eating a wide variety of vertebrate and invertebrate species.
NCRN monitors amphibians in both streams and wetlands. Wetlands are visited four times a year—twice in spring to do visual surveys for egg masses and adult amphibians and twice in summer to dip-net for larval amphibians. Streams are visited twice each year—leaf litter is searched and cover objects are turned to find adult salamanders. Any amphibian malformations are recorded.
Measures of amphibian populations include: proportion of area occupied and occupancy. Calculations take into account variations in the likelihood of detecting species at a site due to their behavior, habitat, and other variables. These measures also allow us to test specific hypotheses about factors influencing amphibian distributions.
The NCRN has monitored amphibians in stream and wetland habitats since 2005 at the Chesapeake & Ohio Canal National Historical Park and Rock Creek Park. Prince William Forest Park stream habitat was added in 2006 and Manassas National Battlefield Park wetlands in 2007.
Between 2013 and 2016, NCRN prepared for the possibility of expanded amphibian monitoring by mapping amphibian habitat at Antietam National Battlefield, Catoctin Mountain Park, George Washington Memorial Parkway, Harpers Ferry National Historical Park, Monocacy National Battlefield, National Capital Parks - East, Prince William Forest Park, and Wolf Trap National Park for the Performing Arts. Starting in 2015 an additional "rotating round" of park monitoring has been added each year.
- Determine trends in proportion of area occupied for viable populations within wetland and upland habitats of NCRN parks.
- Determine the distribution of amphibian species and document the proportion of area occupied by amphibian species in the parks.
- Provide information to aid in the generation of hypotheses for determining causes of differential abundance or long-term changes in proportion of area occupied among species, habitats, and areas.
- Identify and evaluate management actions to reverse declining trends or to increase the occupancy of potential habitats.