A 2026 study found that young Yosemite toads were much more likely to test positive for the chytrid fungus Batrachochytrium dendrobatidis (Bd) after their first winter dormancy than before it. The increase was observed across surveyed cohorts, but researchers have not determined whether the toads picked up the fungus while dormant, carried infections that intensified over winter, or experienced both.
What researchers found in young Yosemite toads
Ecologist David Daversa and colleagues surveyed Yosemite toads at six meadow complexes in the Tioga Pass region of Yosemite National Park from 2021 through 2023. The study included more than 1,800 samples across three years and multiple life stages. For the key comparison, researchers looked at first-year toads before and after their first terrestrial dormancy, often called brumation.
As an Amazon Associate I earn from qualifying purchases.
Science News reported that about 23 percent of the young toads tested positive before that first brumation, compared with more than 90 percent after they emerged. Fewer than half of breeding adults tested positive in the study comparison. These figures describe the sampled toads and periods; they are not fixed rates for every Yosemite toad population or year. The primary paper describes the pattern as infection “proliferation”—an increase in observed prevalence and/or intensity (Daversa et al., Functional Ecology, 2026; Science News, September 2026).
Free tools Windows power users keep installed
One-click scans. No signup required.
Did the toads catch the fungus in their winter burrows?
The study shows that Bd infection signals increased across the winter period in the surveyed young toads. It does not show exactly when or where each infection began: researchers did not directly observe fungal activity inside the toads’ winter burrows.
#1 Best Overall
The authors discuss two possible explanations. An infection that was present at a low, undetectable level before dormancy could have intensified enough to register on later tests. Alternatively, toads could have acquired new infections during dormancy. Both processes may have contributed; the available evidence does not resolve the question.
Bd is a chytrid fungus that infects amphibian skin and can cause chytridiomycosis. Its infective stage is aquatic, and the pathogen is commonly associated with moist, cool environments. That makes the observed winter increase in terrestrial dormant hosts notable, but it is not proof that transmission occurred underground. UCLA’s account of the study describes the result as a surprise for a pathogen generally understood as aquatic (UCLA Newsroom, October 1, 2026).
Why the first winter matters
The findings point to a seasonal period that disease monitoring may otherwise miss. Yosemite toad brumation generally runs from roughly October to May, with timing varying by elevation. If infection becomes more detectable or intense during that interval, sampling only during active seasons could leave an important part of the disease cycle unexplained.
Quick wins for a faster PC:
Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →The study focused on first-year metamorphs in one Yosemite region over three years. It does not establish that the same pattern occurs in every Yosemite toad population, with every Bd strain, or in other amphibian species. More work is needed to distinguish infection acquired during dormancy from infection that was already present and later intensified.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What this means for Yosemite toad conservation
Yosemite toads are high-elevation amphibians of the Sierra Nevada and are federally listed as threatened. Bd is one concern among several. The National Park Service also identifies disease, pollution, drought-related failure of tadpoles to complete metamorphosis, wildfire, reduced winter snowpack, and hotter, drier summers as threats (National Park Service, “Species in the Spotlight: Yosemite Toad,” updated April 26, 2023). The winter study adds detail to the disease picture; it does not show that Bd alone explains population declines.
UCLA reports that the finding has informed a reintroduction program involving Yosemite National Park and the San Francisco Zoo: managers release captive-reared toads after they have grown for a few years, when they are less vulnerable to overwinter Bd infection. The available account does not provide measured long-term survival or population-growth results for this revised release approach.
Quick Recap
How visitors can avoid disturbing Yosemite toads
- Do not touch Yosemite toads.
- Stay outside sensitive, closed, or roped-off areas.
- To report an observation, contact the National Park Service Aquatic Wildlife Program at 209-379-1437.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
