by Elizabeth Blaker :
When Erika Nowak was a child she roamed the meadows and woods of her family’s farm in upstate New York. One day she came across a pair of garter snakes joined in mating and she killed them. When her father saw what she had done, he was thoroughly disgusted with her. Her father, a toll collector by night and hobby beef farmer by day, was given to contemplation and reading. He spoke with Ericka about useful animals and how good various snakes are for the farm because they often eat small rodents. “It completely changed my perspective,” the adult Erika Nowak told me after recounting this story. This was the moment in which the reflexive aversion humans seem to have for snakes was replaced by curiosity and a desire to know more about these animals. Erika is now a herpetologist and Associate Research Professor at Northern Arizona University, working to save the declining narrow-headed garter snake, a highly specialized predator of small fishes in the cold water streams that tumble over the edge of the Colorado Plateau and down the face of the Mogollon escarpment.
There are approximately thirty species of garter snakes and ribbon snakes in the genus Thamnophis, all of which live in North or Central America. Many of these are terrestrial, or land dwelling, while a few are aquatic. Snakes evolved from lizards millions of years ago, losing their legs and developing long slender bodies which allow them to slide into narrow places. The lengthening of the body required major changes in the layout of the snake’s internal organs. The right lung became enlarged and greatly lengthened while the left lung shrank to be very small in some and completely absent in other species of snake. In some water snakes, the trachea, or windpipe, has modifications that allow it to soak up additional oxygen. The kidneys are also elongated, but offset so that right kidney is closer to the snake’s head than the left kidney, and the same with the testicles. All male snakes and lizards have two penises.
The two penises are called hemipenes. Research shows that if the male mates more than once in a day, the two penises are used alternately. Only one penis is used for each mating. Each penis is connected to its own testicle where sperm is made and stored. I once asked one of my biology professors how the snake knows which penis was used most recently, and she said that she supposed it may have to do with stretch receptors in the testicles that provide a physical sensation of fullness or lack thereof.
Most of us have seen a garter snake darting through the grasses, and perhaps admired the yellow stripes down its sides. Narrow-headed garter snakes have blotchy spots rather than stripes to better hide against the background of rocky stream bottoms. As the name suggests, they have narrow heads, with eyes positioned nearer to the top of their heads than other garter snakes, an adaptation that allows them to look up through the water while lying in wait for unwary small fish at the bottom of the stream. An observant and lucky person may come across a narrow-headed garter snake coiled in the branches of a stream-side willow, enjoying a bit of sunshine. When it sees you the snake will drop out of the branches and dive to the bottom of the stream where it can stay for at least a half-hour at a time.
Andrew Holycross, a herpetologist at Arizona State University, told me about seeing narrow-headed garter snakes hunting in the wild in a recent interview. “They spend a lot of time at riffles waiting for native fish to come.” When a fish happens along the snake’s head darts forward and it grabs the fish in its jaws. The narrowness of the head reduces the drag in the water as the snake strikes, making it fast and lethal.
Holycross was hired by the Arizona Game and Fish Department a few years ago to survey areas where these snakes had been found previously to determine if the population is truly in decline. A narrow-headed garter snake is a connoisseur of small soft-finned native fishes, and will ignore tadpoles and other morsels that other species of aquatic garter snakes adore. This makes the narrow-headed garter snake particularly vulnerable to disturbances in stream habitats that impact native fish. When I asked Holycross what it was like to conduct the population surveys, he said, “It was depressing. I’d go to a site and search for snakes, and it was like, zero. Zero snakes. Where are they? They were here, and now they’re not.” While surveying the San Francisco hot springs area in New Mexico with another herpetologist, they used minnow traps that have been used successfully in the past for catching narrow-headed garter snakes. “We went back [to check the traps] and NO snakes… They’re gone. You go up river and they are still there in a few of the tributaries, but in the San Francisco there’s a calcium sediment that’s sticking to the bottom of the stream, we don’t why, but it’s different than it used to be,” he said. Both Holycross and Erika Nowak agree that a prime suspect in the decimation of the narrow-headed garter snakes is the crayfish.
Crayfish were introduced to Arizona waters decades ago as food for non-native sport fish and as bait. The crayfish reproduced and slowly spread up the rivers, creeks, and tributaries, where they eat young native fish, frogs, tadpoles, snakes, and streamside vegetation, and burrow into the creek bottoms causing the once clear water to silt up. Studies comparing locations of crayfish and narrow-headed garter snakes show that the two species do not coexist well. Where the crayfish abound, narrow-headed garter snakes have disappeared or persist in very low numbers. The crayfish may be changing the creeks chemically as well as physically, and may even be raising the water temperature. Narrow-headed garter snakes seem to prefer cooler water.
Because the snakes are in a precipitous decline, the US Fish and Wildlife Service, the Arizona Game and Fish Department, and other organizations partnered with the Phoenix Zoo to try to establish a captive breeding program. If the snakes produce offspring in captivity, these can be released in various places where the snakes used to live. But it turns out that narrow-headed garter snakes are very difficult to keep in captivity. Stuart Wells, a biologist at the Phoenix Zoo’s conservation center, has his work cut out for him. To reduce stress that could interfere with survival and breeding, Wells has created large, naturalistic stream habitats with cobbled bottoms and running water. He takes exquisite care of the snakes, monitoring health, feeding, behavior, and body weight. Last year one of the captive narrow-headed garter snake females finally got pregnant, but she was unable to carry her offspring to term. Narrow-headed garter snakes give birth to live young. Wells and his team have recently constructed large climate controlled habitats that can be opened to the outside, with riffles of running water and small pools. He hopes this will help. They have already developed successful captive breeding programs for the endangered black-footed ferret and the Chiricahua leopard frog, so perhaps they will succeed with the narrow-headed garter snake, too.
One of the few remaining strongholds of the narrow-headed garter snake is Oak Creek north of Sedona, Arizona. Oak Creek is a stunningly beautiful creek that courses through a narrow canyon cut into the Mogollon escarpment. The area is incredibly rich in the diversity of plants that hug the banks of the creek, like tall white-barked Arizona sycamores, a multitude of wild flowers all summer long, and rare plants like the Arizona bugbane that require the humid microhabitat at the confluence of springs with the creek. Here Erika Nowak follows in Andrew Holycross’ footsteps as she tries to learn all she can by conducting catch and release surveys, measuring and weighing snakes, and trying to follow them using tiny radio transmitters implanted in the snakes. She watches over the snakes with great concern.
This area of Oak Creek attracts millions of tourists each year who come to play in the water and enjoy the beauty of the red rock canyon. Unfortunately, the activity of large numbers of people in the creek can damage the creek bottom and cause blooms of the intestinal bacteria E. coli. Nowak and her teammates have even seen people catch the snakes and try to bring them home to their gardens, perhaps thinking they would be beneficial or decorative. Unfortunately, narrow-headed garter snakes cannot survive away from the creek, so taking one away condemns it to death. Anglers fishing the creek have confessed to Nowak that they have killed narrow-headed garter snakes thinking they were venomous water snakes. The narrow head gives the snake a slight viper-ish look. Some people simply hate snakes and react by killing them.
I admit that I am not a person who loves to handle snakes, or communes with them at eye level the way I like to do with my dog. Snakes seem alien to me; they have a strange cold look in their eyes. But they are, as are all living things, a triumph of millions of years of evolution, dazzling in their variety and beauty, and there are so many mysteries yet to be learned about them. They are part of an intricate web of life, so complex that scientists are only just beginning to understand some of the interwoven connections among animals, plants, and their environment. I hope the narrow-headed garter snake lives on to hunt beneath the laughing waters of Oak Creek for millennia to come, and that it will eventually repopulate the other chilly mountain streams to which it is so perfectly adapted.