October 18, 2011

The Amazing Disappearing Frogs

This summer we focused much of our research effort on resurveying known mountain yellow-legged frog populations in Sequoia and Kings Canyon National Parks. We first surveyed these areas for amphibians and fish 11-14 years ago and found mountain yellow-legged frogs to be pretty common. Since then, on multiple occasions we've resurveyed the subset of sites that had contained mountain yellow-legged frogs during the original surveys, but no resurveys have been conducted since 2007. So this year, as soon as the snow and ice of winter were gone, we started at the southern border of Sequoia National Park and made our way north, resurveying every site at which mountain yellow-legged frogs were found during the original surveys. By summer's end, we'd covered all of the sites in Sequoia and most of those in southern Kings Canyon National Park. 

Results from this year's resurveys painted a pretty grim picture. Seventy-five percent of the revisited sites were now without any mountain yellow-legged frogs, and in some cases frogs had been extirpated from entire basins. Where frogs were still present, populations were generally much smaller than they had been 11-14 years ago. Many of these remnant populations appear to be spiraling toward extinction, and most of these will likely be gone in another five or so years. For the most part, the resurvey results were as we had expected. The amphibian chytrid fungus (Batrachochytrium dendrobatidis: "Bd") has spread through this region during the past decade, and the outcome of Bd arrival is invariably the collapse of mountain yellow-legged frog populations. What previously had been a reasonably "froggy" landscape was now one in which remaining populations were small and widely scattered. This summer, it was common to go several consecutive days and not find even a single mountain yellow-legged frog. 

But there were a few welcome surprises. In a couple of spots, mountain yellow-legged frog populations had rebounded to levels that far exceeded what we'd seen at these sites in recent years. And this had occurred despite the fact that frogs in these populations remained infected with Bd. Plans are now underway to use small numbers of frogs from these "persistent" populations to reestablish frogs at nearby sites from which they were extirpated following Bd arrival. I'm under no illusions that this will be easy, but we've got to try. The realization that mountain yellow-legged frogs are now gone from vast expanses of Sequoia and Kings Canyon National Parks, and that their disappearance is having far-reaching consequences for these ecosystems provides all the motivation I need to keep on trying.

Back to The Mountain Yellow-legged Frog Site.