Anybody Have a Spare Pond?

The ongoing severe declines of mountain yellow-legged frogs in the Sierra Nevada make it all but inevitable that these populations will eventually be listed under the federal Endangered Species Act. Such a listing will trigger the writing of recovery plans for Rana sierrae and Rana muscosa, plans that will undoubtedly call for the development of captive breeding programs. If successful such programs could provide frogs for reintroductions back into the wild and for experiments that are critical to our understanding of important issues related to frog conservation.

As I've discussed in previous posts captive breeding has an increasingly important role to play in species conservation programs but because maintaining frogs in artificial environments (e.g., indoor aquaria in zoos) is very labor intensive (think of the time required to feed 100 frogs every day, change their water, and clean their enclosures), this gets expensive in a hurry. A cheaper and potentially more productive route would be to hold frogs in natural or semi-natural ponds outdoors. This would greatly reduce the resources needed to maintain these populations because the frogs could feed themselves. All we need are some ponds that would provide suitable habitat for mountain yellow-legged frogs. Ideal ponds would be located at elevations above 6000', be deep enough to allow frogs to overwinter (>10 feet), and have reasonable access. Ponds would also need to be surrounded with a frog-proof barrier to ensure that frogs don't wander off.

If we can't locate such ponds we need to consider constructing them. As I write this I'm staring out the window at my back yard, wondering if maybe we could replace that useless lawn with a frog pond. But seriously, we need to engage any interested agency or member of the public and provide the resources necessary to make this happen. Might there be a national forest ranger district out there with a pond near a district office that could be turned into a frog pond? Are there any private landowners who might be willing to have one of their ponds put to such a use?

If any of you readers have any ideas I'd love to hear them.

Back to The Mountain Yellow-legged Frog Site.

One Fewer Frog in the Forest

Research by Karen Lips and others on amphibian declines in Central America has made clear that the scope of these declines is unprecedented in modern times. In recent years dozens and perhaps hundreds of Central American amphibian species are thought to have been driven to extinction by the amphibian chytrid fungus. The following article provides a glimpse at one of those amphibians, the Panamanian golden frog. This species is a national icon in Panama but is now believed to be extinct in the wild (link). The only individuals still in existence are those housed in a captive breeding facility in Central America. For additional information about this iconic species, check out www.ranadorada.org.

Back to The Mountain Yellow-legged Frog Site.

Once Upon a Time....

I remember with crystal clarity the day I realized the impact that the amphibian chytrid fungus (Batrachochytrium dendrobatidis - Bd) was having on mountain yellow-legged frogs in the Sierra Nevada. It was July 2000 and my field crew and I were surveying lakes and ponds along the Monarch Divide and Cirque Crest for amphibians and fish. I'd been as excited as a little kid to get into this area and see some of the most remote lakes in the Sierra, places where several years earlier a backcountry ranger had made observations of many mountain yellow-legged frog populations. When the trip was over 20 days later I felt like I'd been hit over the head with a hammer. The future of frog restoration in the Sierra Nevada had just gotten a lot more complicated than I ever imagined it would be.

Up until that trip the available data on Bd and its impacts was still sparse and remained an abstraction to me. The observations made by Dave Bradford 20 years earlier of frog die-offs in western Sequoia National Park were worrisome but were surrounded by enough uncertainty regarding the cause that I wasn't paying those observations much attention. Afterall, for the past five years I'd surveyed hundreds of lakes and the effects of fish were as clearcut as could be. But there were a few lakes that I'd run across during all of those surveys that did give me pause. There were those lakes near Pavilion Dome that contained fabulous frog habitat but in which I found either no frogs or only the decaying carcasses of frogs that had died the previous winter. And that lake between Lake Basin and Dumbbell Basin where I'd seen lots of frogs during a backpack trip in the early 1990s but by the time we surveyed that site there wasn't a frog to be found. These observations nagged at me but still lacked any broader context. In contrast, my recent analyses of survey data from more than 2000 lakes had clearly shown the negative effect of fish on frogs, and early results from two fish removal experiments conducted by me and by Vance Vredenburg showed dramatic increases in the frog populations at these sites just a few years after fish removal. Restoration of frog populations wasn't going to be easy because fish were so ubiquitous but at least we had the tools to reverse the decline of the mountain yellow-legged frog. To my eyes, the future looked bright.

The first lake I surveyed on that Monarch Divide trip was at the head of the Gorge of Despair. Looking down on the lake from above I could only smile. There should be gobs of tadpoles in that warm cove on the north side of the lake, I thought, and adult frogs will be sunning by the hundreds on those granite slabs near the outlet. An hour later I had finished the survey and could only shake my head. I'd found only four mountain yellow-legged frog tadpoles and had not seen a single adult. Even more alarming was that the tadpoles were clearly sick. We didn't have an accurate method of detecting Bd in those days but my notes on the datasheet that I filled out that day had an ominous tone: "All four tadpoles were large (~3 years old). The one individual I was able to catch had only a partial beak and no toothrows. Skin had a mottled appearance. Chytrid fungus?". Every subsequent day produced similar observations. In lake after lake where frogs had been abundant just a few years earlier we found either no mountain yellow-legged frogs or only a few tadpoles, all with mouthpart deformities suggestive of Bd infection.

Twenty days later, surveys completed and out of food, we hiked down the Copper Creek trail to Cedar Grove. On that long hot descent I struggled to put all of the pieces together. Frog die-offs in western Sequoia National Park in the 1970s and 1980s, healthy frog populations throughout the eastern portions of Sequoia and Kings Canyon National Parks, and now evidence of recent and ongoing die-offs along the Monarch Divide and Cirque Crest.... Could it be that Bd had been spreading from west to east across this part of the Sierra Nevada since the 1970s and that even those huge frog populations in places like Barrett Lakes Basin and Sixty Lake Basin might someday also succumb to this plague? The thought sent shivers down my spine and haunted me for years.

I called Dave Bradford the next day and before I could describe to him what we'd seen on our trip I somewhat immodestly blurted out, "I know what wiped out your frogs on the Tablelands - the chytrid fungus!". I don't know what he thought of my remark or the subsequent description of lake after lake with hardly a frog to be found, but I had seen the future of the mountain yellow-legged frog and it filled me with a profound sense of dread. All that I knew was about to change and the frogs that to me had become as much a part of the Sierra Nevada as the towering granite peaks were soon to be pushed aside by an unseen and unstoppable force.

And so it has come to be. Many of the lake basins where I counted thousands of frogs in the late 1990s are now frogless. When I walk along a lake shoreline no frogs jump into the water from their grassy hiding places. The shallows where tadpoles used to congregate by the thousands on warm afternoons, thrashing frantically in their retreat to deeper water when I approached, are calm and placid now. The mayflies and beetles are still in abundance in the nearshore waters and on the surface the lakes are as beautiful as ever, but these lakes are profoundly changed, perhaps forever. The same could be said of that idealistic young biologist....

Back to The Mountain Yellow-legged Frog Site.

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....

Back to The Mountain Yellow-legged Frog Site.

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.

Back to The Mountain Yellow-legged Frog Site.

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.

Back to The Mountain Yellow-legged Frog Site.

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.

Back to The Mountain Yellow-legged Frog Site.