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Tracking Down the Coastal Patch-nosed Snake

For nearly 15 years, staff at the Institute for Conservation Research has studied reptile ecology and movement on the 800-acre Biodiversity Reserve at the San Diego Zoo Safari Park. Our work has shown that we have a healthy population of coastal patch-nosed snakes Salvadora hexalepis virgultea on the property, a species I have always been interested in.

This snake is considered a California Species of Special Concern and is often referred to as rare. Because of its rarity, there is a paucity of information on the patch-nosed snake’s general biology and there has yet to be a scientific publication on its ecology. This year I finally began my project.

My plan was to capture at least 10 animals and implant them with radio transmitters so I could follow their movements and study their ecology. On normal rainfall years I see an average of about 8 of these wonderful snakes, so I figured that if I actively searched for them, I would be able to get a very good sample size for the study. However, I did not count on the drought being so intense!

Snakes get most of their water from the food they eat and when there is no water the food disappears as well. Many of our small native animals tend to stay underground during such “tough times” and await better weather. Not only did many of the prey species disappear over the spring and summer but the snakes did too, preferring to stay deep underground to conserve moisture. 

Some snakes and other reptiles came to the surface for a brief period during the breeding season (from April to June) and I was able to find a couple of patch-nosed snakes for my study. Unfortunately, soon after this, reptile activity ceased altogether. On a good spring day in a year with normal rainfall, I can find up to 20 snakes belonging to between 8 and 10 different species.

This year, in stark contrast to normal expectations, my best snake day yielded just two snakes. 

In addition, I spent nearly every day in the field for 7 weeks in May and June and I only saw two rattlesnakes. As the summer progressed and the habitat became more and more dry, very little lizard and snake activity was observed.

The parched year of 2014 was not the best time to begin a patched-nosed snake project, but I did acquire some valuable data. I was able to track an adult male snake over a four month period and I logged a total of 38 localities on him. From that data, it appears that this particular individual favors cactus and stayed in and around the big groves of native prickly pear Opuntia littoralis in the reserve.

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So far, his home range has been recorded at about five hectares, and with more tracking I’m sure his home range size will increase.

During future tracking sessions, we will be able to not only learn the home range size of individual snakes but also study their thermal ecology, diet, habitat preferences and breeding ecology (all of which have never been documented). During the radio implant surgeries, performed by Safari Park veterinarians, we also plan to analyze blood samples for normal blood values, investigate parasite loads and collect samples for hormone analysis.

Our overall goal will be to establish the ecological requirements of this iconic California snake species and the degree to which endangered coastal sage scrub habitat is critical to its survival.

Jeff Lemm, Senior Research Coordinator

 

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