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Desert Amphibians

Field Guide to Amphibians and Reptiles of the San Diego Region The deserts of Southern California are dusty and strewn with cacti, blisteringly hot in summer and utterly devoid of rainfall for months at a stretch. Who would think that amphibians would be able to find a home here?

But salamanders, frogs, and toads all find a way to survive, whether sleeping deep underground or congregating around wet seeps and oases. Nearly 17 species can be found in the deserts of Southern California, though several of them have become extirpated in recent decades and may no longer exist.

The quintessential California desert amphibian is the red-spotted toad (Bufo punctatus), whose high trilling songs fill every desert canyon and waterhole after spring rains. Barely larger than a walnut this hardy toad spends up to 10 months a year buried underground, living off of the water stored in its overly large bladder.

After scrambling from its underground lair, its first order of business is to sit in a puddle of water and drink fresh water through a patch of delicate skin on its belly, then head over to join the evening chorus.

Biologists have learned that amphibians like red-spotted toads and spadefoots awaken from their long underground slumbers when they hear the pulsing resonance of raindrops striking the soil – an effect that biologists can duplicate by putting a small electric motor on the ground. Only when the toads hear a certain frequency of pulses (indicating a heavy rain) or over a certain period of time, will they stir and dig their way to the surface. Amazingly, in parts of the Mojave Desert spadefoots must sometimes wait up to two years for a rainfall that will wake them up.

These are the true desert amphibians, those able to survive for many months with a total absence of rain or surface water. Amphibians that need water throughout the year are limited to springs and waterholes. In Joshua Tree National Park, for instance, the big lumbering western toad (Bufo boreas) is found wherever there is permanent water. And the thin-skinned California treefrog (Hyla cadaverina) – colored like granite and perfectly hidden on the rocks – is restricted to oases and unable to wander cross-country to new sites.

Salamanders apparently have more specialized needs and are limited to coastal areas or islands of wet forest on higher desert mountain ranges. This might mean that salamanders exist in disjunct or relict populations rather than being true desert amphibians, but they are still an unexpected surprise when hikers encounter them. In particular, the large-blotched salamander (Ensatina eschscholtzii klauberi) is a real eye-opener with large brilliant orange blotches arranged on a black background. This lung-less salamander breathes through its moist skin and must stay damp in order to survive. In many areas, the ensatina will crawl into the waterlogged interior of a large decaying log during the dry season.

The problem for nearly all of these organisms, however, is that they live at the very physiological edge of survival. Many populations are isolated and depend on a single water source, rendering them incredibly vulnerable to human disturbance or changing climate. A drying spring, a diverted water source, or even a hiker taking a shampoo bath in a little pool could be disastrous for animals that can’t wander the open desert in search of new water.

If you encounter any amphibians during your visit to the California desert, take a moment to appreciate the complexity and exquisite balance of these creature’s lives. And if you don’t encounter any, rest assured that somewhere in the landscape they are simply sleeping and waiting for the next rain.

David Lukas, co-author of Sierra Nevada Natural History

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