Herpetofauna awaken with the rainy season

An Arizona summer is dry. It’s hot. There’s not a drop of moisture in the air. Life is seemingly absent at first glance as humans are indoors while the wildlife is underground or minimally active in cool shady hideouts. The desert is one of the harshest climates to live in, yet even in the driest of years there is ample life in the desert. However, with the arrival of the monsoon, everything comes out to play! When it finally rains people celebrate, plants become green and lush, and wildlife comes out to quench their thirst. 

The herpetofauna (reptiles and amphibians) of the Sonoran Desert are masters of this climate and have adapted to a life without the luxury of readily available water. Snakes, lizards, and amphibians have impressive adaptations that allow them to survive, and the resources that come with the monsoon season allow them to truly thrive. 

Reptiles can go weeks and sometimes months without water, getting by with just the natural moisture from the food they eat. For example, snakes often eat just a couple times a month so the moisture they consume is pretty low. When the first rain of the season comes through, rattlesnakes will come out of hiding and coil up into a nice tight cinnamon bun, then carefully drink water droplets off their own skin. The arrival of monsoon season also prompts snakes, and many other desert animals, to find mates and reproduce. A rainy year means more plants and seeds, invertebrates, and mammals, which are overlapping resources for one another and food sources for snakes. A robust monsoon season usually translates to higher reproduction rates for reptiles, either that same season or the following year. 

Gila monsters, an icon of the southwest, are found in abundance in the desert as they too enjoy the welcomed monsoon moisture. Gila monsters spend up to 90% of their entire lives underground because they have very porous skin. If they are in the heat too long, any natural moisture can evaporate through those pores making them susceptible to dehydration and desiccation. On the flip side, an advantage of this porous skin is that it’s easy to absorb moisture when it’s available. In fact, water droplets can sink directly into Gila monster skin!  

Toads and frogs also thrive in the desert, despite dry conditions. They do this by spending much of their lives burrowed underground to prevent desiccation. Some species, like the Sonoran Desert toad spend as many as eleven months or more below the surface. During a robust rainy season, amphibians come to the surface and saturate hiking trails and rural roads to take advantage of the buffet of insects that arrives with the rains. Several different species of toad can be found sharing the same trail! 

The monsoons not only bring the desert to life with vibrant plants and beautiful wildflowers everywhere, but they awaken wildlife by providing relief from the oppressive heat of summer. 

To see some of this wonderful wildlife, find a hiking trail (less foot traffic usually yields better results) and plan around the temperature. During the summer rainy season dawn and dusk are great times to spot reptiles, as they tend to avoid the hottest parts of the day.  

Remember to keep an eye out as most reptiles use their camouflage to avoid detection. Amphibians also enjoy the evenings but can be seen in cool areas throughout the day if you have a keen eye. Despite the impressive adaptations to survive in harsh desert conditions, the herpetofauna of the Sonoran Desert truly awakens, and thrives with the arrival of monsoon season.   

When it rains, it floras  

With the desert buzzing with activity and dripping with rainwater, monsoon season is one of the best times to get outside and go exploring. Take the time to look at the plants, recognize them in their supple forms, and relish the joy of seeing life thrive in a time where all its needs are met. 

Of the four North American deserts, the Sonoran has the greatest diversity of life forms due specifically to its biannual rainfall. The Mojave receives primarily winter rainfall, the Chihuahuan summer, and the Great Basin precipitation primarily as snow, whereas the Sonoran receives two rainy seasons. This results in Sonoran Desert plants enduring shorter periods of drought, relatively shorter periods of freezing temperatures in the winter, and hosting many subtropical species.  

With the onset of the summer rains, many plants that lay dormant for most of the year finally get their party clothes out, so to speak. Individual plants will look unfamiliar, having tripled their leaf size, looking plump and happy. Plants will be bursting in bright green foliage, soaking up sunlight and using that energy to put out new growth. Saguaro cacti will swell and grow taller with the rains. Vines will crawl through, up and over the surrounding plants, reaching for sunlight from under the new, dense canopy.  

Many Sonoran Desert plants flower in the dry, early summer months in order to have viable seed ready to germinate during the July and August monsoon rainfall. A series of rainy days is critical to the establishment of seedlings and their ability to put on enough growth to survive the drought periods of the coming fall and next early summer. Some plants that rely on this are saguaros, creosote bush, and other long-lived species that can survive even if successful recruitment only happens once a century or so. Perennial shrubs can be both opportunistic and conservative. Desert globe mallow will use the rain to put out growth and flower at the end of the monsoon season, whereas shrubs like brittlebush will go into flower anytime they have ample water, even though their usual flowering time is late winter.

Annual plants rely on a slightly different approach. The seeds of summer annuals, such as summer caltrop, will often feature a thick seed coat that prevents germination until enough rain events have saturated the soil. These plants must complete their entire life cycle in one season, so they focus not only on growth but also on flowering and setting seed.  

This blog was written by Courtney Christie (Reptile Keeper II) and Grace Stoner (Horticulturalist), with contributions from Kim Duffek (Botanist) and Erik Rakestraw (Botany Department Curator)