Herp Hibernation

Herpetology is the study of reptiles and amphibians. They are often grouped together as “cold-blooded” animals and share similar characteristics, but they are actually separated into two distinct classes (Reptilia and Amphibia) of “herps”  that shared a common ancestor about 350 million years ago before diverging down different evolutionary paths. 

Cold- and warm-blooded are colloquial, over-simplified terms that refer to the way animals regulate their body temperature. Endotherms, known as warm-blooded, refer to animals like mammals who create their own body heat through what we consume. Ectotherms, known as cold-blooded, refer to animals like reptiles and amphibians who can not create their own body heat and must regulate it through their surrounding environment. They are at the mercy of the ambient temperature, which is why you often see lizards and snakes basking in the sun when it’s cold out, and why they are more active during the summer when it is hot.

Juvenile horned lizard (Phrynosoma sp.) seen in the Rincon Mountains, Greater short-horned lizard (Phyrnosoma hernandesi) seen in the Canelo Hills.

As we enter the cooler half of our year, the blazing temperatures can drop to below freezing, especially higher in the mountains like Patagonia. For us, and other endotherms, that means we stay inside more, bundle up, and eat hot food to stay warm. But for ecotherms, like our reptiles and amphibians, they can not create their own heat and are at the mercy of the outdoor, ambient temperature. They’ve adopted different strategies to survive, which is why they mostly disappear for the winter months.

Gila monster (Heloderma suspectum) seen near Bowie, AZ.

But then where do ectotherms go when it’s below freezing? They do not hibernate, but rather enter a state called “brumation” which is similar to hibernation, but specific to herps because they aren’t necessarily sleeping. There are many ways that herps have adapted to overcome winter weather. Snakes usually find a rocky crevice or abandoned den to use as their hibernaculum, or the place they use to hunker down during the winter. Often snakes like to use the same hibernaculum year after year. Some species will cohabitate with other snakes, sometimes hundreds at a time, while others like to spend their time alone.

Black-tailed rattlesnake (Crotalus molossus) in the Chiricahua Mountains, juvenile Western diamondbacked rattlesnake (Crotalus atrox) in the Sonoran Desert.

Semi-aquatic reptiles like the sonoran mud turtle will rest at the bottom of a water source as it begins to freeze over. Turtles have the incredible ability to draw oxygen in through their rear, which is known as “cloacal breathing” which refers to their tail being permeable and able to draw in oxygen when levels are depleted, and the water is frozen over with no way to access the open air.

Sonora mud turtle (Kinosternon sonoriense) seen at Las Cienegas National Conservation Area in February.

One of the Watershed Restoration Program’s projects this year had us visiting riparian areas like at Las Cienegas National Conservation Area, where we were surveying for erosion control needs throughout over 75 miles of canyons. As we slowly criss-crossed our way across the vast open grasslands, some days we’d hike through or drive near Cienega Creek and its headwaters. We were lucky enough to spot turtles swimming under the ice, or even recent turtle hatches, with a dozen or so baby turtles making their way through the muddy water.

Sonora mud turtle (Kinosternon sonoriense) seen at Las Cienegas National Conservation Area.

The aquatic animals have an especially difficult time adjusting to winter, as most of their habitat freezes over, meaning their resources like food and oxygen are severely depleted. Amphibians like the canyon tree frog will retreat underground and go dormant for the winter until the soil temperature heats up in spring in time for their breeding season. 

Canyon treefrogs (Hyla arenicolor) seen in Sabino Canyon and Aravaipa Canyon

I was extra curious about herps after having one of the snakiest summers on the Watershed Restoration Crew. Our crew saw at least 30 snakes, many of them diamond back rattlesnakes, but also non-venemous ones like gopher, king, and patch-nosed snakes. We also saw more turtles and tortoises than ever before. Southern Arizona is a wonderful place to go herping because of the sheer diversity and abundance of reptiles and amphibians. Our generally warmer temperatures make it easier for them to survive compared to harsh winters further north, where some species have adapted by allowing their bodies to completely freeze solid until they thaw out in spring and their hearts start beating again (isn’t that insane? You can learn more about the wood frog here. 

Patch-nosed snake (Salvadora sp.) eating a, possibly, common lesser earless lizard (Holbrookia maculata) at Borderlands Wildlife Preserve.