Prince William Amphibian Monitoring 2023

Wood frog (Rana sylvatica)

NPS / C. Shafer

Home to at least 17 amphibian species!

We monitor wetlands and streams at Prince William Forest Park. Field teams visit wetlands and streams, recording which amphibian species they observe and in which sites. Looking across all sites in a park, they generate a measure of species “occupancy,” that shows what proportion of sites are occupied by a particular species.

We want to know, “is there a change in occupancy over time?”

A few amphibian species are found outside of the wetland and stream environments that we monitor (like terrestrial, red-backed salamanders and burrowing, eastern spadefoot toads). These species may live in the park, but our monitoring is not designed to document them. While we do record incidental sightings, they are excluded from the data analysis.

Wetland Amphibians

In 2023, we observed eight wetland species. Since wetland amphibian monitoring began in Prince William in 2017, a total of 14 wetland species (see Figure 1). Lower numbers in 2023 are the result of fewer visits to monitoring sites. Usually there are two each year. Field crews visited 28 wetlands once in March of 2023.

Wood frogs were the most abundant species detected (roughly 1,255 larvae and 12 egg masses observed). Spotted salamanders, eastern newts, and spring peepers were observed at the most sites (each detected at four wetlands).

See below for how to read this figure!

Wetland Amphibian Occupancy Trends

Figure 1. Graphs showing occupancy probability by amphibian species in wetland pools at Prince William Forest Park.

NPS

Marbled salamander (Ambystoma opacum)

L. Beimfohr

How to read the wetland occupancy figure

• Dark gray bars show the occupancy based on raw amphibian sightings
• Black dots (connected by black lines) are estimates of occupancy. (Estimates help fill in observation gaps since amphibians can easily hide and avoid detection, so that there are usually more individuals present than can be counted by monitoring teams)
• Light gray shaded areas are 95% credible intervals
• "Gray treefrog complex" and "Toad complex" refer to closely related gray treefrog species and toad species are grouped together
• The “Trend” text box at the top of each graph contains a numeric trend value and a color that shows the direction of estimated occupancy trends. Blue is positive, white is neutral, yellow is slightly negative, and red is negative. The numbers in the parentheses represent the 95% credible intervals
• Species are listed in alphabetical order by their common names

Stream amphibians: Occupancy trends

As of 2023, we've observed three salamander species: northern two-lined salamander, northern dusky salamander, and northern red salamander (Figure 2). Field crews visited five streams twice in June and July 2021. No streams were surveyed during the 2022 or 2023 field seasons.

Figure 2. Graph showing occupancy probability by salamander species in streams at Prince William Park (EBIS=northern two-lined salamander, DFUS=northern dusky salamander, PRUB=northern red salamander). Black dots are estimated occupancy values, and grey vertical lines show 95% confidence intervals.

NPS / C. Shafer

These data are preliminary or provisional and are subject to revision. They are being provided to meet the need for timely best science. The data have not received final approval by the U.S. Geological Survey (USGS) and are provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the data.