(originally commissioned for the Living Alongside Wildlife blog)
Venture off-trail in the deep woods and you might come across a bear track. Not the worn path the deer leave, but offset indentations, footfalls landing on top of each other until they are beaten into the earth. The ease of maintained routine suggests that the bear knows a comfort here.
Even if we had missed his steps, the heaps of dung and fresh scrape on the tree would have been hard to ignore. We were in the bear’s domain. This is the sort of place you have to go – up in the mountains, deep in the woods, off the trail – if you want to find native frogs in southern California.
In the 2000s I took part in herpetological surveys throughout the West Coast, one of many amateurs recording reptile and amphibian populations through citizen scientist projects. Now I wanted to return to these wild places and see how the most vulnerable herp populations were coping. What impact had another decade of drought, development, climate change and the spread of invasive species had on their sustainability?
That’s how I found myself well off the beaten path, in the world of bear tracks and tree scrapes, looking for frogs hanging on in their last reserves.
The remote survivor
My father and I woke up that morning to beautiful yellow blooms and buzzing hummingbirds. Whiptail and sagebrush lizards scurried away as we began our hike, highlighting that high elevation SoCal dynamic where dry brush abuts mountain pine. Around one turn a rockfall betrayed someone’s retreat from the canyon rim, the steepness of the source suggesting it may have been a bighorn sheep displacing the stones. A few hours in we were delighted to observe a Coast Mountain Kingsnake crossing our path.
But there were no frogs.
No frogs in the creek. No frogs sunning on the rocks. No frogs in the tributaries. No frogs in the side pools.
The population I was looking for is so small that I couldn’t risk missing anything. I stalked upstream, examining every surface and every depth. By the time I reached the area I knew to be their prime habitat I was scrutinizing everything twice, pausing beforehand to let my eyes creep over the logs and banks in the hope of locating an undisturbed frog before I approached, then checking again from the opposite side as I passed in case a disturbed frog or a different angle would reveal something new.
Years earlier I had found several frogs in these pools. Now, in the same places, I found nothing.
At least they weren’t all gone. Hours into our hike and at least twenty minutes past the point where I had expected to see a frog, I finally spot it. A Southern Mountain Yellow-legged Frog, one of the rarest frogs in the United States.
It was the only frog we saw on this hike.
The fate of the ranids
When you think of a frog, your mental image will probably match a ranid, the family of frogs known as “True Frogs.” Ranids epitomize the prototypical “frog shape” and are the most widely distributed group of amphibians in the world. Yet 99.99% of Southern Californians will never see a native ranid in their life.
This is what happened:
The California Red-legged Frog (Rana draytonii), the “celebrated jumping frog” of the Mark Twain tale, once ranged throughout the southern Californian coastal lowlands. By 1970 it was in trouble as urban development inundated any land that wasn’t mountain or desert. In 1996 the frog was placed on the Endangered Species List and began acquiring habitat protections, but the damage was done. Now it is absent south of Santa Barbara save for two relict populations on the outskirts of LA County. Fledgling reintroductions into new streams are being attempted.
The Foothill Yellow-legged Frog (Rana boylii), previously found in the foothills and middle-elevations of the coast ranges all the way to the cusp of Los Angeles, was unable to deal with dams and stream diversion. Along the coast it is now extirpated south of Monterey County. Inland in the southern Sierra Nevada Mountains only a couple populations are hanging on.
The Southern Mountain Yellow-legged Frog (Rana muscosa), at one point surveyed in over 165 high-elevation mountain streams, has been reduced to ten small populations scattered across the San Jacinto, San Bernardino, and San Gabriel Mountains. Dams and development did their damage, but the most comprehensive blow may have been the introduction of carnivorous trout to fish-less streams. The largest of the existing populations is now only a few dozen frogs. Reintroduction efforts are underway, but in recent years existent populations have blipped out faster than the new ones have taken hold (in fact, the frogs may actually be down to only 7-8 populations). More viable but still endangered populations of this species are found in the southern Sierra Nevada Mountains.
There are still frogs in Southern California. The two chorus frog species that provide a soundtrack for many a Hollywood movie, Pseudacris cadaverina and Pseudacris hypochondriaca, have maintained much of their historic range and even persist in some city parks. Invasive bullfrogs from the east coast are a ravenous presence.
But for half of the state, the native ranids are almost gone.
Toads in low places
I emerged from the tent and laced on my hiking shoes, lathered with quaternary ammonium the previous night to prevent the spread of frog-killing chytrid fungus. There was a long hike ahead and the sun was coming up hot. But I had a question well worth the effort.
Had any Arroyo Toads (Anaxyrus californicus) reproduced this year?
When looking for cryptic species, larvae are a cheat code. The mass reproductive strategies common in amphibians (known biologically as r-reproduction) ensure that many more tadpoles are produced than will ever become adults, and these tadpoles concentrate in specific habitats. Most years that you search for the Arroyo Toad, tadpoles will be the easiest way to find them.
But this isn’t most years. California’s 2018 was a drought year, one of the worst recorded (though 2015 was as bad or worse, an ominous warning about how frequent such droughts are becoming). And Dr. Sam Sweet had warned me that Arroyo Toads in the coastal ranges hadn’t bred at all this year. Sam, a UCSB ecologist who monitors coastal amphibian populations, had suggested that the lack of early rain kept those toads and other aquatic amphibians from getting the signals they needed to start reproduction.
I wanted to know if the inland populations were the same.
That query is what led to a sixteen mile round-trip hike in the sun. By some estimates there are only twenty or so viable populations of Arroyo Toad left, and every one is vulnerable. I was heading to an area where surveyors just a decade earlier had located hundreds of tadpoles in half-a-dozen breeding locales. Would they still be around this year?
The early portion of the hike was promising. A Great Basin Collared Lizard sunned on a rock, one of five lizard species spotted along the route. A few minutes later a California Kingsnake slowly paralleled the trail. Unlike the previous hike this route was well-trafficked, and so there were some human encounters too.
I took advantage of the maintained trail and passed most of the rocky stream without a look. Arroyo Toads employ a reproductive strategy which requires open, sandy banks (Sam posted a fascinating breakdown of the Arroyo Toad’s unique habitat ecology here). If you don’t have the banks, you won’t find the toads. Unfortunately, the flatter, slower sections of creek necessary to build such sandbanks are only found in certain canyons, and those canyons were often the first to get dammed.
Three hours later I reached the target spot. I scanned sandbanks for juveniles and poked around vegetation in open pools and within the shade of boulders. Not all of the flat spots were contiguous, so it took a couple hours of climbing up the canyon and then dropping back down to the water to check every likely spot. Sweat began pouring off my arms.
And all I found were bullfrogs.
Bullfrogs are a bane to native herps. Introduced to California a century ago, they reproduce in warmer, dirtier, and more human-altered waterways than native frogs can tolerate, but spread right through many of the best native-frog habitats as well. The adults will eat everything they can get their mouths around.
On this day bullfrogs were the only amphibian I could find in the pools. Had the season been too dry for the toads’ mating cues? Was there a viable population of adults still hiding under the sand, waiting for the next good rain? Thankfully, Arroyo Toads have a lifespan of around five years and 2017 was a great season for rain. But four years of droughts hit before then, limiting the number of toads that were left to breed. More drought is on the way.
In the early evening I backtracked six miles to reach a different locality by nightfall. Adult Arroyo Toads are active in the early night, and I was hoping some would be around even if they weren’t breeding. As I got closer to civilization I began seeing more casual day-trippers, including locals with jeeps and 4WD pickup trucks who had driven right up to the creek. The sandy banks that Arroyo Toads love are a target destination for partiers who splash through the pools, cut cookies in the sand, and then relax with drinks on the peaceful shores.
As darkness fell the partiers and off-roaders disappeared. A pair of beavers patrolled the pond they had created in a sluggish stretch, slapping the surface of the water when I approached. As I pushed through the brush to reach an open bank, fluttering led me to a California Towhee, trapped by fishing line entangled around one of its feet.
I freed the towhee and was rewarded minutes later by a lone Arroyo Toad sitting on the sand bank. They don’t have much to them aesthetically, but I found it gorgeous. Unfortunately, I didn’t hear any calls on this bank, and over the course of an hour and a half of searching in prime activity time I only heard a couple quickly aborted trills.
Walking through Arroyo Toad habitat gives a sense for how profoundly we alter even that habitat we haven’t developed. Trash litters the area. Makeshift roads cut through the same banks that the toads bury themselves into. And there may not be an historic Arroyo Toad locality left in the Transverse Ranges that can be approached without passing a dam.
Dams are the #1 enemy of stream-breeding amphibians like the Arroyo Toad and Foothill Yellow-Legged Frog. It’s obvious that building a dam destroys most animal populations in the newly flooded area. But the full impact is much worse – the dam also prevents downstream spots from getting flooded when they most need it (in winter to maintain sentiment banks) and creates artificially high flow when they least need it (in summer when such flows wash away eggs and tadpoles). Soon not only the populations in the flooded area but all populations downstream of the dam are wiped out, leaving smaller populations isolated in narrow canyons upstream. These disjunct remnants are too far apart to reinforce each other and become vulnerable to traumatic events. The floods of 1969, which may have wiped out the last remaining Foothill Yellow-legged Frogs in the San Gabriel Mountains, were one such event which would not have been so devastating if the populations hadn’t already been cut back and isolated.
As I took my leave of the stream, a Big-eared Woodrat emerged from a gap in the canyon wall. A Botta’s Pocket Gopher rustled in the dead leaves next to the trail. My presence spooked a Striped Skunk, which then ran off into a nearby boulder field and nearly smacked straight into a beautiful Bobcat. While watching the bobcat I found a Baja California Chorus Frog (Pseudacris hypochondriaca) in a pond. Later a Western Toad (Anaxyrus boreas) would cross my path (Western Toads utilize a wider range of habitat than the much more endangered Arroyo Toads), while Burrowing Owls watched from the slopes above.
Even as I mourned the significant human impacts, it was a blessing to see that there was still wildlife to call this spot home.
Frogs are not doing well on the southern California coast. Besides the species I already named, the Western Spadefoot (Spea hammondii) is also extirpated from 80-90% of its historic range here, largely due to development and agriculture in lowland habitat. The Western Toad (Anaxyrus boreas), once among the most ubiquitous amphibians in southern California, seems to be retreating from many of its historic localities as well. And it’s not just frogs – other reptiles and amphibians reliant on water, such as the California Newt (Taricha torosa), Southwestern Pond Turtle (Actinemys pallida), and California Red-sided Garter Snake (Thamnophis sirtalis infernalis), are meeting the same fate. Even terrestrial herps on the California coast have seen their ranges shrink.
Southern California is vulnerable to development for obvious reasons. But it shouldn’t be seen as a unique case. The basic issues of development and dams and poor allocation of water resources are issues that afflict human communities everywhere, and unless you’re off the grid completely then you yourself are in some part contributing to the demand.
The more we develop, the more we build, the more we consume, the more populations of frogs will wink out. What are those of us complicit in this consumption to do with human development and all that comes with it?
References:
Thomson, Robert C. California Amphibian and Reptile Species of Special Concern. University of California Press. Kindle Edition.
Nafis, Gary. California Herps: A guide to the reptiles and amphibians of California. http://www.californiaherps.com/
I want to thank Sam Sweet, Jeff Lemm, and Chris Rombough for some insights on particular species.
A huge thanks to Shanti Mathias for her editing and suggestions.
Reptiles and Amphibians of Thailand 