They may not be as majestic as an elk or as photogenic as a pika, but Rocky Mountain National Park is home to four amazing species of amphibians with unique characteristics: the boreal toad, the chorus frog, the wood frog, and the tiger salamander. With its protected status, Rocky has also been an important area for research to study and monitor amphibian populations.
The Oxford Dictionary defines an amphibian as a cold-blooded vertebrate animal with an aquatic gill-breathing stage typically followed by a terrestrial lung-breathing adult stage—they spend parts of their life cycle in water and on land.
The boreal toad (Anaxyrus boreas boreas) might be the most familiar amphibian in Rocky because as early as the 1970s, scientists recognized a precipitous decline in population due to the deadly chytrid fungus. Resource managers and scientists from Rocky, Colorado Parks and Wildlife (CPW), and the U.S. Geological Survey (USGS) have collaborated in a multi-year effort to study and reintroduce breeding populations in the park. Reintroduction sites are carefully selected wetland areas that have specific habitat characteristics suitable for all life stages and are tested to ensure they are free of the deadly fungus.
Jonathan Lewis with a boreal toad. Photo credit: NPS
As part of this effort, some toads have been fitted with passive integrated transponders so they could be identified over time (similar to pet owners having their pets “chipped”). Some toads were fitted with radios so they could be tracked. Captive-bred “sentinel toads” were released to provide information on the suitability of specific sites for reintroduction.
In 2024, park staff and volunteers released 14,913 tadpoles at three different reintroduction sites. Each year, portions of egg masses are collected from wild breeding populations, transported to a CPW research hatchery, and reared to tadpoles where their survival greatly increases in a protected hatchery environment. Just before metamorphosis into their terrestrial forms, the tadpoles are transported and released with hopes to initiate new breeding populations.
The Conservancy has provided financial support for this project since 2019 and has approved $45,000 in 2025. These funds support disease sampling and tadpole release efforts at historic breeding ponds and reintroduction sites.
Much smaller than the toad, and a lot louder (boreal toads don’t call), is the chorus frog. As its name implies, the chorus frog (Pseudacris maculata) has a distinctive call used in attracting mates. Some describe the sound like taking a fingernail and “strumming” the tines of a comb. One frog is loud; many together can be perceived as almost deafening. Despite their impressive vocalizations, at just an inch or less in length, the frogs are secretive and hard to find. The chorus frogs in Rocky tend to be green or tan, but color can vary by location and population.
Wood frogs (Rana sylvatica) are bigger than chorus frogs (up to about 3.3 inches), and they add to the soundscape with a chuckle-like call. They occur only on the park’s west side at elevations of 7,900-9,800 feet. These frogs are known as a “glacial relicts” because they are believed to have survived in pockets of refugia as glaciers developed, covering most other parts of their large range.
A National Park Service online article referred to these frogs as a “biological miracle” due to their unique winter adaption for hibernation. Unlike most frog species whose body temperatures may drop to, but not go below, freezing, wood frogs’ superpower is the ability to literally freeze solid for up to eight months. Boreal toads and chorus frogs also hibernate, but not to the extreme of physically freezing.
The paper describes the incredible process: “At the beginning of winter, ice quickly fills the wood frog’s abdominal cavity and encases the internal organs…At the same time, the wood frog’s liver produces large amounts of glucose that flushes into every cell in its body. This syrupy sugar prevents the cells from freezing and binds water molecules inside the cells to prevent dehydration. So on the one hand, the wood frog’s body allows ice to form around the outsides of cells and organs; and on the other hand, it prevents ice from forming inside the cells, thus avoiding lethal damage.”
In spring, the wood frog thaws from the inside out, starting with the heart, brain, and finally the legs that start to move. With a short season for reproduction, the frogs immediately migrate to a breeding pool.
Another interesting amphibian superpower scientists have recently found is that many bioflouresce. In 2021, researchers Erin Muths, Benjamin LaFrance, Andrew Ray, and Amanda Kissel were interested in whether Rocky’s tiger salamanders (Ambystoma tigrinum) also shared this ability to “absorb visible and ultraviolet light and re-emit it at a lower energy level.”
salamander displays its ability to bioflouresce. Photo credit: NPS | Andrew Ray
Their challenge was to capture highly mobile salamanders underwater at twilight. Photographing the salamanders under white light and under blue light did reveal biofluorescence. Scientists continue to investigate this phenomenon, with some hypothesizing that bioflouresence may enable the nocturnal salamanders to detect each other more easily.
Rocky was previously home to the northern leopard frog which can live at elevations as high as 11,000. The species has been extirpated in the park and its populations have been declining throughout Colorado—a reminder of the need to monitor and support micro-fauna.
If Rocky’s amphibians are a special breed, so, too, are the biologists and resource managers that study and work to conserve these populations. Like their amphibian subjects, researchers often need to be “nocturnal,” working in the chilly overnight hours in ponds and wetlands tracking creatures that can be hard to find, track, and capture. For one USGS biologist studying Rocky’s amphibians, that meant searching for toads one night a week at each study site in the park from June through October!
At the direction of Congress, the USGS established the Amphibian Research and Monitoring Initiative (ARMI) in 2000 to study the status of amphibians on federal lands. ARMI, along with multiple federal partners, including NPS, recognizes May 4-10, 2025 as “Amphibian Week” to celebrate these creatures whose attributes are not just fascinating but have medical relevance for humans in areas such as treatment of diabetes and pain relief.