Bend Bulletin - Climate change becomes latest threat to embattled Oregon spotted frog

This article was published on: 03/8/22 4:37 PM

Drought conditions in Central Oregon threaten to hold back gains being made in restoring water to the Deschutes

Dams in the Deschutes River, along with the canals that siphon water away from it, have sent Oregon spotted frog numbers in decline for decades. Now scientists worry that Oregon’s megadrought could be making things worse for the frog.

Bridget Moran, head of the Bend field office for the U.S. Fish and Wildlife Service, said researchers are still working to understand long-term frog population trends, but short-term trends indicate that oppressive heat waves are taking a toll on frog habitat.
Oregon spotted frogs rely on cool weather in the Pacific Northwest for stable and moist conditions in the rivers, lakes and marshy areas they inhabit. Hot weather that lowers stream flows and dries up river banks reduces the areas where the frogs can breed and lay their eggs, ultimately reducing the numbers of this already threatened species.

“Clearly, a hot and dry summer is not good for any aquatic wildlife in the Pacific Northwest because they are entirely dependent on the typical conditions, which are cool temperatures and sufficient water supply,” said Moran.

Fewer egg masses

Researchers are finding fewer egg masses during springtime surveys, pointing to an overall decline in frog numbers. The most recent data from U.S. Fish and Wildlife Service comes from the spring of 2020. Last year’s numbers are still being processed and won’t be available until this summer, but the year-by-year trend remains clear.

“Across the range of species, in areas where we had hundreds of egg masses, we had under 100 in the most recent counts,” said Moran. “In the places where we located just 10 egg masses, we would have had about 50 in the past. It was a very challenging year for wildlife.”

Egg masses are globular spheres that hold hundreds of tiny frog eggs. Oregon spotted frogs lay eggs in the spring in shallow, still or slow-moving water or in wetland vegetation.
Wildlife biologist Jodi Wilmoth said last year was especially bad for the spotted frog and their eggs on the Upper Deschutes area. While working in the area, Wilmoth said she spotted “many” of the egg masses stranded along the Little Deschutes River. Due to unusually dry conditions, the water level at which the frogs had laid the eggs had dropped to the point where the eggs were drying out.

“I have been doing egg mass surveys since 2018 and had never seen this level of stranding. There’s a good chance that 2021 was a catastrophic year for Oregon spotted frog egg mass survival along the Little Deschutes,” said Wilmoth.

Temperatures in Central Oregon surged into the triple digits for several days in late June last year, one of the hottest on record. The extreme heat wave melted off much of the Central Oregon snowpack, depriving rivers and streams of badly needed late-season flows.

Drought hurts all species

The spotted frog is not alone in trying to survive these challenging circumstances. Fish also struggle for survival as river and stream levels decline. Pronghorn, antelope and sage grouse are also affected when climate change dries up plants and waterholes, depriving them of sustenance.

Deer and elk also suffer in times of drought because it’s harder for them to bulk up on fat that they need for winter.

“Drought reduces food available for pronghorn, and makes the survival of fawns less successful,” said Erik Fernandez, wilderness program manager with Oregon Wild. “Similarly, sage grouse chicks don’t actually eat sage until they are a month or so old. In the meantime, they don’t have as many small plants and insects to feed on.”

Andrew Walch, district wildlife biologist for the Oregon Department of Fish and Wildlife in Bend, said the dry seasons are getting longer, reducing the time that plant life has to green up.

“When it’s crazy-dry in March and April, you are not getting that green forb production out on the desert, which is not good for sage-grouse populations,” he said.

Walch said a number of factors contribute to the downward trend of sage-grouse numbers, including habitat loss and habitat alteration, but climate change is part of the mix.
“It is noticeable when we do our spring surveys how dry it is out there. Normally it’s muddy or snowy and frozen, but it’s really dry now and it’s looking like it’s going to be the case again this season,” said Walch.

More stressors

When it comes to pinpointing exactly what threats affect frogs the most, it gets complicated. In the Upper Deschutes, it is widely recognized that dams and diversions for agriculture have the greatest impact on frog populations, but the small amphibians have other threats, too.

“There is agricultural development, livestock grazing, non-native grasses grow in the area where they like to breed, bullfrogs eating them, it’s not just climate change. They are getting hit by a lot of things,” said Andrew Blaustein, biology professor emeritus at Oregon State University. “But when the climate changes, the entire ecosystem is screwed up.”
Some environmentalists say the drought-related problems affecting the frog can be mitigated with better river management.

The frog “has survived past climate changes and was here for eons, and was an abundant frog before all these changes,” said Noah Greenwald, endangered species director for the Center for Biological Diversity.

Greenwald said a more “common sense” approach to managing the Deschutes is needed for the river to become more resilient. He says changing water laws to make them more equitable for all farmers would be a good start.

“If we manage it better, then we could have a healthier river for Oregon spotted frogs and irrigation for farmers even with what is happening with climate change,” said Greenwald “I think that is possible.”

Canary in the coal mine

Until a healthy river can be achieved, the Oregon spotted frog and other species that rely on its consistent flow are likely to continue on a downward trend or disappear altogether. Moran from the Fish and Wildlife Service said keeping a close eye on the frog is critical not only for its survival but also for the survival of other species.

“The Oregon spotted frog is a canary in the coal mine, if you will,” said Moran. “For the public, I think it’s an indication that our ecosystems are not healthy and we need to do something to help restore them.”

Restoration of the Upper Deschutes ecosystem may depend partly on the intensity of climate change, but another factor is still the impact that people have on the river. Modernizing inefficient irrigation systems and leaky canals is within the power of the irrigation districts. Invasive species, such as bullfrogs, can be mitigated with culling work. Damaged riparian areas can be also restored and protected from development.

“It’s really many of these factors we are working on to reduce the pressure on the spotted frog,” said Moran. “So we can see the benefit of those long-term increases in Deschutes River flows.”

Reporter: Michael Kohn