40 years of toads

OREGON—Pacific Northwest Research Station research ecologist Deanna “Dede” Olson first hiked to the northwest corner of Lost Lake, in the Oregon Cascade Range, to track western toad (Anaxyrus boreas) populations in 1982. It was the first time she witnessed a breeding aggregation of western toads. She caught, marked and released nearly 100 toads from a lake chock-full of the species, allowing her to verify nonrandom mating sexual selection. Leapfrog forward 40 years and much has changed.

Now, Lost Lake is literally lost come summertime. Although Olson has since found breeding toads to observe at Three Creeks and Todd Lake, a breeched lava tube in the lake now causes it to drain annually by July. She says toads are no longer able to survive there. But all is not lost.

Overall, toad breeding populations in the Cascade Range seem to be faring fine, despite climate change reducing the snowpack. There is only an issue if early-summer lake levels subside rapidly, leaving the eggs high and dry. Olson says she once observed a million toad eggs lost when laid in very shallow water during a drought year.

Mass mortality events for toads have multiple causes. The water mold saprolegnia has infected and killed entire cohorts of eggs; and research shows that UV-b radiation can exacerbate these infections. Another threat is predator ravens that have learned how to turn the toads’ skin inside out to avoid eating the neurotoxin in their warts. This predation pressure could explain the toads’ very short and explosive breeding season, which lasts only a few days.

Then there is the chytrid fungus. Olson says that the fungus spread through the Todd Lake site in the mid-1980s. As a result, one year when she handled the toads, they shed their skin, now known as a symptom of chytridiomycosis. The next year, male toad counts plummeted.

Threats to amphibians and conservation actions to counter the threats are now part of Olson’s research portfolio. One focus of land managers in the Pacific Northwest has been developing mitigations to ensure forest amphibians can survive timber harvest activities—for example, by determining a safe width for riparian buffers that skirt headwater streams. Another focus is the threat of emerging infectious diseases.

Promoting concern for amphibian health is a multifaceted task that requires educating many different stakeholders with varying land-use perspectives. Olson is helping to integrate the perspectives of disease ecologists in the field and disease diagnosticians in the laboratory with land managers who decide which, if any, mitigations to implement.

Such disease management is essential to sustaining wildlife health as well as healthy ecosystems. Olson’s work contributes to local, regional, national and international efforts aligning to conserve the toad populations she studies and benefits many other species as well. This year Olson celebrates 40 years of observing amphibians; taking notes, conducting research and protecting them.

Deanna “Dede” Olson, Pacific Northwest Research Station research ecologist, studying toads at Lost Lake in 1982, 2007 and 2021. USDA Forest Service photo.

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