Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 32, Number 8;   August, 2005

Combat in the Prairie Rattlesnake

by Young Cage

At the end of this summer, I was invited to visit a study site in New Mexico where large numbers of Prairie Rattlesnakes (Crotalus viridis) have been caught, weighed, measured, sampled, and PIT-tagged. In addition, transmitters have been placed in some individuals so they can be followed by researchers. In that way a great deal of data have been gathered on growth, diet, times of activity, sexual activity, response to temperature and rain, and many other factors. Other snakes are involved in similar studies at the site, including Western Diamond-backed Rattlesnakes (Crotalus atrox), Common Kingsnakes (Lampropeltis getula), Gopher snakes (Pituophis catenifer), and Coachwhips (Masticophis flagellum).

So I was very interested and ready to gather information as we drove up. And of course, I had my Pentax ready for action.

After introductions and throwing our gear in appropriate spots, we drove out to check on a female viridis living in or near a kangaroo rat mound. She had a transmitter, but since she had been located earlier in the day, our guides knew right where she would be. As we approached, however, something remarkable was observed. Two heads were bobbing up out of the sagebrush, moving about vigorously. As we got a little closer, it became obvious that we were witnessing prairie rattlesnake male combat, something I had not seen in any rattlesnakes.

I was aware of male combat in diamondbacks, as it is observed occasionally and even seen by my neighbors in the Tortolita Mountains. But it is not observed often in Crotalus viridis, so we were seeing something special.

There appeared to be a rather dominant male, and it was determined by lack of paint on the rattle that it was probably a new animal. The dominated male had paint on its rattle, and was determined to be the one called "Mexico" by the researchers. It had been hanging around the female.

The female, a minor role player in the action, was deep in the mound. She was already gravid, with birthing anticipated in the next week or two. The fact that she was gravid would have seemed to lessen the chances of male combat, but she was also opaque. The prevailing theory was that the shedding process heightened pheromone production and release, and that triggered the response by the males.

The two males were aware of us, crouching or sitting down 6 m (20 ft) or so away. I had worked around to the other side, to put the sun at my back for photo opportunities. The two continued with their battle, every once in a while stopping to eye us. At no point did they show any aggression towards us. They did, however, work their way towards me, eventually getting within 0.6 m (2 ft). They were preoccupied, but still eyeing me occasionally.

I was getting "great advice" at the time - "make like a rock," "don't move, nothing to worry about," "don't worry, your heat signature is washed out by the warm soil" and so forth. I know that you can get focused (no pun intended) behind a camera and lose track of what an animal in front of you is doing. That can be tricky, and I prefer an extra hand when shooting venomous animals. But I was comfortable as long as others were verbally updating me.

The match itself was very intense. We observed much wrestling, occasionally hissing and rattling, some bloating of the throats and bodies. On a couple of occasions there would be a very aggressive "throw" where the dominant male would simply slam the other to the ground with a loud thump; we saw that maybe three times.

The dominated male tried to get away on a couple of occasions, heading for the mound. The other male would catch up, re-engage, and they would be right back to it. At one point the dominated male made it to the mound, and headed down one of the many holes. The other followed him. I figured that was the last we would see of them, but after five minutes or so, as we were discussing this incredible observation, out they came.

They resumed combat. As it was getting dark and we had no lights, we left one of us to observe what he could; the others went back to camp to resupply and start dinner. The whole event was observed for approximately three and a half hours.

The next morning, what we assume to be the dominant male was observed coiled next to the female, both out on the side of the mound. She was very wary, sliding quickly into one of the holes. The male was captured, and processed later that day, then returned to the identical spot. We found the other male, "Mexico", about 60 m (120 ft) away, quietly coiled in deep grass.

This was a wonderful chance to observe nature at its most interesting. I believe there will be several descriptions about this event in scientific papers. How cool to have been there.

One thing that seemed very interesting was the ritualistic nature of the "combat." Either animal could have bitten the other, likely envenomating its opponent. But they never did, as if they understood there was nothing to be gained by that destructive behavior.

During our three days we observed quite a few other snakes. The Coachwhips were tan and brown, quite different from our normal Tucson black ones. Common Kingsnakes were also in evidence, with a quite pretty splendida look. I thought I found my first Salvadora grahamiae (Mountain Patch-nosed Snake) west of Texas, but it turned out to be a very pretty pastel hexalepis (Western Patch-nosed snake), apparently typical of the area.

I found a Sonora semiannulata (Groundsnake) crossing the scrub and crawling in a small bush. I thought the Sonora we found at Redington Pass this spring to be the prettiest I had seen, but this one easily surpassed it. Beauty is in the eye of the beholder, but it would take an awfully pretty animal to surpass this one. It was a great wind up for a fun trip.

Many thanks to Matt Goode, Kevin Baker, and Sarah Denardo for helping me on this trip. They were great company, and great naturalists to hang around with.