Counting Amphibians on Mount Rainier's Roads: Night Surveys Find Hot Spots

On rainy nights, Mount Rainier National Park staff crawled along park roads at 5 miles per hour looking for frogs and salamanders. A park science brief explains why: roads cause vehicle collisions, maintenance disturbance and restoration projects that all affect amphibians, and the surveys were meant to show where amphibians cross, to help reduce those impacts.

A coastal tailed frog (Ascaphus truei). NPS photo.

The park and its roads

Mount Rainier National Park is in west-central Washington, on the western slope of the Cascade Range. Its more than 236,000 acres are 97 percent designated wilderness, and the road system makes up 0.13 percent of the area. Visitation exceeds one million a year, peaking in summer.

The surveyed roads on the south side of the park: Paradise Road, Paradise Valley Road, Stevens Canyon Road and Highway 123. NPS graphic.

How the survey worked

The four roads form an almost continuous transect across the park's west and east sides, with elevations from 1720 to 5400 feet and a total length of 41.6 miles. They cross several vegetation zones and major glacial rivers and run beside many aquatic habitats.

Surveys ran at night from April through November during or after rain, when the road was mostly wet and temperatures were above freezing. Most were done by vehicle at an average of 5 mph, with occasional walks over leaf litter or debris, using low beams and fog lights. This pace let the crews see juvenile frogs and small plethodontid salamanders. Surveys started no earlier than an hour after sunset and tried to finish an hour before sunrise. Each animal was identified to species, measured and located, and road-killed animals were collected. Live ones were moved off the road to the side they were facing.

What they found

In 24 survey nights, with 59.9 search hours and 138.6 miles driven on the 41.6 miles of road, the team detected 1243 amphibians. Twelve of the 14 species known in the park turned up on the roads, including two species of concern, the Larch Mountain salamander and Van Dyke's salamander.

A Larch Mountain salamander (Plethodon larselli), one of the two species of concern. NPS photo.

The two roads with the widest elevation range each had the most amphibian species, 11. Coastal tailed frogs were on all four roads. Most hot spots on the map reflect tailed frog numbers, except on the lower Paradise road, where the road crosses wetland and upland habitat and several pond-breeding species live.

What the authors make of it

The large number of coastal tailed frogs was unexpected. The authors suggest the frogs are drawn to wet pavement, much as snakes are drawn to warm pavement, and when approached they crouch flat on the road, which may help explain the 55 percent mortality they saw. The brief says the map has become a resource for park managers to reduce the effects of road rehabilitation and maintenance on amphibians and to weigh options at known hot spots, and the authors hope to follow up with a more rigorous survey method.

Sources

• Mount Rainier National Park science brief, "Mapping Amphibian Occurrence on the Road System at Mount Rainier National Park," by Anthony S. Anderson, Darin D. Swinney and Rebecca A. Lofgren (Mount Rainier National Park), https://www.nps.gov/articles/000/mapping-amphibian-occurrence-on-the-road-system-at-mount-rainier-national-park.htm; rewritten in hubnx's own words. The brief's overall road-kill percentage does not divide evenly by its totals, so it is not repeated here.