Rock Creek Park Amphibian Monitoring, 2023

A wood frog (Rana sylvatica). NPS / C. Shafer.

Rock Creek Park in Washington, D.C., is home to at least nine amphibian species. The Park Service monitors its wetlands and streams.

What is measured

Crews visit the park's monitoring sites and record which species they find where. Across all sites, that gives occupancy: the share of sites where a species is present. The question: is occupancy changing over time?

Some species live away from the habitats monitored — red-backed salamanders on land, eastern spadefoot toads underground. They may be in the park, but the survey isn't designed to find them; chance sightings are noted but left out of the analysis.

Wetlands in 2023

• Species seen: four — of nine wetland species recorded since monitoring began in 2005.
• Visits: 13 wetlands, three of them new this year, each visited once, in March 2023. There are usually two visits a year, which is why the numbers are lower.
• Most abundant: wood frogs (750 larvae), then American bullfrogs and northern green frogs. Each species turned up at one wetland.

Figure 1: occupancy of each wetland species at Rock Creek Park. NPS / C. Shafer.

Reading the charts

• Dark gray bars: occupancy from raw sightings.
• Black dots and lines: estimated occupancy. Amphibians hide well, so there are usually more present than crews can count; the estimate fills those gaps.
• Light gray bands: 95% credible intervals.
• "Gray treefrog complex" and "Toad complex": closely related species grouped together.
• "Trend" box, atop each graph: a number and a color for the direction of the estimated trend — blue rising, white neutral, yellow slightly falling, red falling. The numbers in parentheses are the 95% credible interval.
• Species run alphabetically by common name.

Streams

Stream sites weren't visited in 2023. In 2022, the last year surveyed, crews found two salamanders: the northern dusky and the northern two-lined. The two-lined was the most abundant — five adults, four juveniles and 57 larvae — and was at the most sites.

Figure 2: occupancy of stream salamanders. EBIS: northern two-lined; DFUS: northern dusky; PRUB: northern red salamander. Black dots are estimates; gray lines, 95% confidence intervals. NPS / C. Shafer.

The data are preliminary and may be revised; they have not had the U.S. Geological Survey's final approval.

Sources

Based on "Rock Creek Amphibian Monitoring 2023," part of the series Amphibian Monitoring in the National Capital Region, National Park Service; a work of the United States government in the public domain.