Save the Frogs Day - April 28 2009

April 28, 2009 is the first annual Save the Frogs Day. Check out www.savethefrogs.com/day for more information.

The San Francisco Chronicle had a story on efforts to combat the amphibian chytrid fungus in their 2/19/2009 edition. The battle continues....

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Salamanders Declining in Latin America

My research on amphibian declines focuses almost exclusively on mountain yellow-legged frogs. As such, it is easy to forget the fact that the amphibian decline phenomenon has a global reach and that these declines affect a huge diversity of amphibian species. Compared to the large body of evidence showing declines in frogs and toads, evidence for salamander declines has been sparse but a new paper in the Proceedings of the National Academy of Sciences (available here) brings these declines into startling focus. Rovito et al. describe the disappearance of multiple salamander species from montane sites in Mexico and Guatemala (figure from paper showing these declines is shown to left). Surveys conducted at the study sites in the 1970s turned up more than 70 salamanders per visit but surveys in 2005-2007 at the same sites turned up fewer than five salamanders per visit. Several of the most common species during the 1970s were not found during any of the recent surveys and may be extinct.

Given the very high diversity of salamanders in the Neotropics these declines suggest that many salamander species may be at much higher risk of extinction than has been appreciated. Unfortunately the cause of the declines described by Rovito et al. remains obscure. The amphibian chytrid fungus was detected on some salamanders at the study sites and could be a contributing factor as could climate change.

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Captive Breeding Inches Closer to Reality

A couple of weeks ago, I attended the annual meeting of the Amphibian Populations Task Force in Bodega Bay. The dozens of talks over two days provided an abundance of new data from a wide array of amphibians in California and Nevada. Perhaps the most relevant information for conservation of the mountain yellow-legged frog was the announcement that the captive population of southern mountain yellow-legged frogs (Rana muscosa) being maintained at the San Diego Zoo (see my previous post for details) had produced a clutch of eggs. To my knowledge this is the first time mountain yellow-legged frogs have bred successfully in captivity. The ongoing reproductive activity of animals in the captive population has raised hopes that numerous additional egg masses might yet be laid this year. If such success continues this captive colony might play an important role in the recovery of these highly endangered frog populations in southern California's Transverse Ranges. (The above photo shows an R. muscosa egg mass from the Sierra Nevada.)

Although I have strong reservations about using captive breeding as a primary strategy to conserve mountain yellow-legged frogs, the southern California populations are in such bad shape that captive breeding may be one of the best options left. Populations in some parts of the Sierra Nevada remain robust enough that captive breeding is not yet needed. I hope we never get to the point where captive breeding of these Sierran populations becomes necessary. But if we do need to go this route in the future, it is somewhat reassuring to know that the techniques to house and breed these frogs in captivity are already being developed.

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Effects of Frog Declines on Bears in the Sierra Nevada

A few years ago, Dave Graber (Chief Scientist, Pacific Southwest Region of the National Park Service) asked me a question that I've never been able to get out of my head. Dave, who studied black bears in the Sierra Nevada for many years, asked me if there was a connection between the dramatic decline of mountain yellow-legged frogs in the 1970s and the coincident increase in the number of bears frequenting campgrounds and mountain towns. As an example, he mentioned that black bears were essentially absent from the eastern Sierra until the 1970s, and today the town of Mammoth Lakes alone is home to dozens of dumpster-diving ursines. I'm afraid my answer was little more than "we know that bears feed on frogs so the potential exists for frog declines to affect bears". Unfortunately we'll never know the answer to Dave's question because mountain yellow-legged frogs no longer play the important ecological role they once did as the most abundant vertebrate in the Sierra Nevada.

But what do we know about this frog-bear interaction? Over the years we've made numerous observations of bears feeding on frogs. Those I made in a fishless basin in Kings Canyon National Park in 1997 still haunt me today. This unnamed basin has never been stocked with fish and in 1997 virtually every lake was full of mountain yellow-legged frogs and tadpoles. Frog counts from that 1997 visit were 11,330 frogs and 107,750 tadpoles. During that time it was rare to walk around a lake without stumbling across numerous bear shits. In a shallow cove of one lake, tadpoles aggregated by the thousands to take advantage of the warm water found there every afternoon. Bear tracks ringed the cove shoreline and frequently veered into the lake where tadpoles were particularly dense. The only way to make sense of these observations was if bears were feeding on the abundant tadpoles. The frog population in this basin crashed about seven years ago due to chytridiomycosis, and during recent visits bear sign seems much scarcer than it was 12 years ago.

I've witnessed something similar in Humphreys Basin following fish removal and subsequent frog recovery. In 1997, Marmot Lake contained lots of small trout and a few mountain yellow-legged frogs. Following fish removal, the frog population exploded and more than 3,000 frogs exist at the lake today. As the numbers of frogs increased so did my observations of bear sign which had been nonexistent during all of my previous years spent at this lake. Marmot Lake doesn't seem like typical bear habitat given its very high elevation but it is now not uncommon to see bear tracks all around the lake shoreline. I'm guessing that the motivation for such shoreline ambulations are the little frog snacks found there.

Given the historic abundance of mountain yellow-legged frogs in the Sierra Nevada I suspect that frogs were often included in bear diets. And maybe, just maybe, the decline of frogs has driven bears into campgrounds and towns in search of alternate food sources. Maybe someday those backcountry lakes will once again contain an abundance of frogs sufficient to interest a hungry bear.

So, as I've said many times before, although the frog restoration issue is often couched simplistically as "fish versus frogs", the issue is in fact much broader.

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