Manassas Amphibian Monitoring 2023

Wood frog (Rana sylvatica)

NPS / C. Shafer

Home to at least 13 amphibian species!

We monitor wetlands at Manassas National Battlefield. Field teams visit wetland pools, 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 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 10 wetland species. Since amphibian monitoring began in Manassas in 2008, we have observed a total of 13 wetland species (see Figure 1 below). Field crews visited 27 wetland sites two times between March and May of 2023, except for Blue House Pool which was visited once.

Wood frogs were the most abundant amphibian detected (4,067 larvae and 211 egg masses). Wood frogs were also observed at the most sites (9 of 27 wetlands), followed by northern green frogs and spotted salamanders.

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 Manassas National Battlefield.

NPS

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

Spotted salamander (Ambystoma maculatum)

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.