Research indicates that juvenile Yosemite toads are highly vulnerable to the deadly chytrid fungus while hibernating underground during their first winter.

Surveys conducted in Yosemite National Park reveal that young Yosemite toads frequently emerge from their first winter hibernation infected with the lethal chytrid fungus, Batrachochytrium dendrobatidis (Bd). While the fungus is typically waterborne, the findings published September 23 in Functional Ecology suggest that underground burrows present an unexpectedly high risk for the amphibians during their months-long brumation.

Fungal prevalence in juvenile toads

Researchers led by UCLA ecologist David Daversa captured toads of various ages to test for the presence of the fungus. While roughly 23 percent of juveniles tested positive for Bd before their first winter, more than 90 percent emerged from their burrows in the spring with infections, some of which were severe. In comparison, less than half of the mature breeding adults tested positive for the fungus.

Conservation and research implications

The exact mechanism allowing the waterborne fungus to thrive in underground burrows remains unknown, though researchers suggest it could spread through communal burrowing or the growth of previously undetectable infections. Consequently, a reintroduction program involving the San Francisco Zoo and the U.S. National Park Service has shifted its strategy to focus on releasing mature toads that have already passed their most vulnerable life stages.