“All amphibians are tethered to the pond by their evolutionary history, the most primitive vertebrates to make the transition from the aquatic life of their ancestors to life on land.” — Robin Wall Kimmerer 

While not all amphibians, toads, frogs, newts, salamanders, and the like, are tethered to ponds, most are tied to water in one form or another to complete their life cycle (one group, slender salamanders seem to be an exception). Unlike birds and reptiles that lay yolk-filled, shelled eggs to protect their growing embryos from the climate vagaries of the world around them, amphibian eggs lack both shells to protect the embryo from desiccation and a yolk supply to nourish the growing embryo. These reproductive traits tie reptiles and birds as closer relatives to each other than either are to amphibians.

Amphibians were the first vertebrates to explore solid, dry ground beyond the shore of an otherwise completely aquatic existence, but their reproductive approach is still very much fish-like. An amphibian egg hatches quickly, often within just a few hours or days, producing not a miniature of its adult form, but a fish-like larva, aka tadpoles or polliwogs. They hatch either with gills or the ability to absorb oxygen through their skin, which must stay wet. They must actively seek and consume food in order to metamorphose to an adult form with lungs and legs. The distinction between toads and frogs often focuses on their skin’s moisture and texture. While frogs also tend to have larger, more powerful hind legs, if its skin is smooth and moist, you’re likely looking at a frog. If it’s dry, rough, and bumpy, you’re likely looking at a toad. Frogs tend to spend much if not all their lives in water, whereas a toad uses water primarily just to breed. So, frogs need water available, if not year-round, at least for many months. In contrast, toads can be found some distance from water and can successfully breed even when surface water is present for just 3-5 weeks

Desert amphibians, mostly toads, are remnants from a time when what are now our North American deserts were much wetter, as was the case during the last glacial maxima of the Pleistocene Epoch. It was cooler and it rained a lot more. Rivers and lakes were common across what we now call desert. It was a good time to be a toad, as there were dependable wetlands and, compared to today, lots of them.

With the end of the glacial maxima, starting maybe 10-14 thousand years ago, that all changed. The wetlands began to dry up or at best become ephemeral. Lakes and rivers became playas and dry washes. Mammoths, mastodons, ground sloths, camels and horses all disappeared, shifting to Asia and Africa, or going extinct. The continued existence of toads here in the Colorado Desert in what today is one of the driest, hottest deserts of North America, is therefore just short of miraculous, yet they are here. They survive because they can burrow into the alluvial sands and wait for years until wet conditions are just right.  When conditions suit their needs they emerge, hydrate and gorge on small insects, eat, breed, and then return to their entombment until those wet conditions return. This year warm summer temperatures plus tropical storm Hilary, and the monsoon storm that followed close on her heels, brought out red-spotted toads in abundance in a handful of the narrow desert canyons. A couple months later, little one-inch long toadlets trying their best not to be stepped on were evidence of their parents’ survival skills.

There are as many as six toad species that can be found here in the Colorado Desert, from the Coachella Valley extending south into the Imperial Valley toward the Colorado River. The most common is the red-spotted toad, with characteristic red "warts" on its back, small round parotid glands, and lack of a white mid-back stripe.

Just to the north in the Mojave Desert there are just two toads, red-spotted and western. The features that are the best clues for identifying which toad species you might have found include parotid gland shape, pattern and lines on their back, pupil shape, and voice. Parotid glands are puffy swellings behind a toad’s ear which contain toxins aimed at deterring would-be predators. In red-spotted toads they are round. In Woodhouse's, Great Basin, Sonoran, and western toads they are oblong. In western toads, which are mostly found on the western side of our mountain ranges and scattered through the Mojave Desert, the parotid glands are small, only slightly longer than the diameter of its eye. Parotid glands in Great Basin and Sonoran toads are 2-2.5 times as long as their eye diameter. In Woodhouse’s toad their parotid is at least four times as long as their eye’s diameter.  Couch’s spadefoot toads lack visible parotid glands. Western, Woodhouse’s, and sometimes Great Basin toads all have a white line down the middle of their back. The others lack such lines. Markings on the back of western and Woodhouse’s toads are bumpy and random, whereas on Great Basin toads their markings are paired, mirror images on each side of their center line. Most toads’ eyes have horizontal pupils; only the spadefoot toads have cat-like vertical pupils.

If you explore the desert at night, particularly after a series of soaking summer rains that leave standing water, you might hear the mating calls of our desert toads. Red-spotted toads use a melodious trill. Woodhouse’s call sounds like a human baby in distress, very disconcerting indeed. Back in the 1970s, University of California Riverside professor Wilbur Mayhew spent much of his time studying desert lizards. Back then, after hurricane Kathleen inundated parts of the Coachella Valley, he went out to what is now the Coachella Valley National Wildlife Refuge’s desert sand dunes at night to listen for toads. He reported a cacophony of Woodhouse’s toads. Today they appear to be gone, no sounds at night and no toad tracks in the dried mud following tropical storm Hilary.

This underlines the challenge of documenting and evaluating the status of desert toad populations, species that spend so much of their time underground waiting for the right amount of rain at the right time of year. They appear to be able to wait many years, but there are clearly limits. Once, while searching for fringe-toed lizards on that same National Wildlife Refuge I found the mummified body of a Couch’s spadefoot toad. It turned out to be the first and only record for that species in the Coachella Valley. Never seen here before and never since, but was it an anomaly or the last of what was once a sustainable population? Both Woodhouse’s toads and Couch’s spadefoot toads are still reported further south in Imperial County along the edge of the Algodones dunes. Why there and not the Coachella Valley’s sand dunes? Maybe it’s the frequency of summer rains, maybe it’s the artificial, irrigation water availability there but less so in the Coachella Valley.

A decade or so ago I, along with the biologist for the Boyd Deep Canyon Desert Research Station, Mark Fisher, visited colleagues, scientists studying sand dune lizards in the Chihuahuan Desert of north-central Mexico, in the state of Coahuila. The Chihuahuan Desert is defined by the amount of summer rain it receives (along with the near complete lack of winter rain), and that year the summer rain was particularly bountiful. The low-lying areas were all inundated with standing water; fortunately, their access roads were all engineered to be just a few inches above the surrounding water. As we drove those roads going between sand dune sites, I have a vivid memory of the road surface being covered with a living layer of toads, which fortunately hopped aside as we drove slowly ahead. Couch’s and Mexican spadefoot toads, green toads, red-spotted toads, and Great Plains toads. From a toad’s perspective this was clearly a healthy environment, and supports the hypothesis that summer rains are important to the vitality of desert toad communities.

 Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe.