Drought scorches amphibians
Although the exact details won’t be known until months or years from now, the drought that is drying up ponds and streams throughout Colorado and across the country appears to be affecting wildlife in significant and diverse ways. Those animals that rely on aquatic habitats may be hardest hit—not only fish but their amphibious neighbors, the frogs and salamanders that call western Colorado home.
In summers like this, it may be hard to imagine the hot, dry Grand Valley as home to many amphibians—and it seems it might be home to slightly fewer, for a while at least, in the wake of this record-setting drought.
From the chorus frogs and boreal toads found on Grand Mesa to the tiger salamanders that wash down from there, the red-spotted toads along Colorado National Monument to the canyon tree frogs tucked up in the monument’s canyons, the spadefoot toads in their burrows out by Grand Junction Regional Airport to the Woodhouse’s toads common throughout town, the amphibian population here is surprisingly large and diverse.
But a number of factors have taken their toll on amphibians throughout the hemisphere, including in Colorado—and the drought is only compounding those struggles.
About 39 percent of western hemisphere amphibian species are threatened with extinction, according to the Global Amphibian Assessment, largely due to habitat loss from agriculture and development and the rapid spread of a chytrid fungus that has already wiped out some populations and species.
The long list of other threats that have made amphibians the most imperiled class of animals today includes environmental contaminants, climatic changes and invasive species.
Though Caribbean and Central American species are the most imperiled, 21 percent of North American amphibian species are threatened, especially those found at higher elevations. In Colorado, the boreal toad has been listed as endangered by the Colorado Division of Wildlife, largely due to the spread of the chytrid fungus, including on Grand Mesa.
Amphibians here also face other threats, including diseases and parasites spread by leeches and ticks, said Steve Werman, a molecular biologist and herpetologist at Colorado Mesa University.
“Drought could clearly affect amphibians,” he said. “And if drought weakens them a little bit, that can stress them and allow diseases and other things to get in. They would be more susceptible to things they would normally fend off.”
The main impact from drought arises from the drying up of ponds where some amphibians breed.
After winters with low snowpacks, such as this year’s, there are fewer of those breeding sites, according to Stephen Corn, a herpetologist with the U.S. Geological Survey’s Missoula, Mont., office.
With Colorado State in the 1970s and early 1980s, Corn studied leopard frogs in the Red Feather Lakes north of Fort Collins. During the course of those studies, several populations went extinct following the drought of 1976-77, he said.
“The dry winters led a lot of sites to dry up over winter, and frogs never really came back to these sites for the most part,” Corn said. “If we see long-term drought that really dries up amphibian habitat, that has a chance to have effects.”
The scope of those impacts depends on species, and species that move to temporary breeding ponds to reproduce are expected to be impacted less than those that remain in a permanent habitat that may dry up and leave the animals with nowhere to go.
“You see expansion and contraction in those species that use temporary habitats, but in those that use permanent habitats, like leopard frogs, those impacts can be much worse,” Corn said.
Boreal toads, he noted, stay in their habitat rather than moving to temporary breeding grounds, potentially adding drought impacts to their plight.
“Certainly when you have multiple things, they’ll have a harder time coming back than if it’s just drought or just fungal outbreaks,” Corn said.
CMU’s Werman noted salamanders and canyon tree frogs could also be in that category, potentially stuck with a dried-up pond. The exact extent of that damage will not be clear immediately, he said, as dry ponds can affect populations both this year and next.
Spadefoot toads, for instance, typically stay underground and are fine if there is no rain, but they can be impacted if they stay underground for multiple years.
“It takes a long time to see impacts — more than a year,” noted Erin Muths, with USGS’s Fort Collins office, though she did say one frog pond she studies in Cameron Pass west of Fort Collins was completely dry already. It usually stays wet through mid-August.
“The big thing is these breeding ponds. If these dry up really fast that can really decimate a local population,” Werman said. “Anything with an aquatic water stage is going to be hurt.”