Two nights ago I was finishing up working outside after dark. In summer I prefer to work after sundown because it is cooler and more pleasant than being in blazing hot sun. One of the final tasks remaining was to pivot the solar panels that operate my water pump eastwards in time for sunrise the next morning, since having the panels facing directly at the morning sun (and then pivoting them again at about 1 PM to face westwards for sunset) enables me to pump almost 50% more water in the course of a day than if I just leave them always facing southwards only. On the pathway heading towards the well, I came across a modestly sized (about 24 inches / 60 cm long) Western diamondback rattlesnake (Crotalus atrox) coiled demurely in the middle of the drive. This is why I always carry a light around at night – you never know when you will cross paths with a well-camouflaged venomous snake out here in the desert, and stepping on one in the darkness could be medically devastating. But no worries in this case. I calmly walked around it and went to rotate the panels as per my original intention.

Upon returning down the same path a few minutes later, I shone my headlamp ahead of me to where the snake was, and saw that it was now gone. The snake had decided to relocated off of the path. Figuring that it probably had not gone far, I scanned the surrounding desert for it, and saw it partially coiled underneath a buckhorn cholla (Cylindropuntia acanthocarpa) cactus to the left of where I was, about 15 feet away from where it had been.

That was when I saw a small Merriam’s kangaroo rat (Dipodomys merriami) hopping along within a few feet of the waiting snake. Transfixed and seized by a sudden jolt of anxiety on behalf of the rat, I watched it approach the reptile, unaware of what was likely to happen next. When it wandered blithely to within about a foot, the snake struck the rat squarely and retreated to the coiled position. (It also rattled and raised its head in a standoff display, probably aimed at me, which it probably wouldn’t have done had I not been standing right there with my light observing the scene. I suspect that my presence altered the snake’s behavior and sense of threat, since there would otherwise have been no real reason for the snake to bother – it would just have bitten the rat and stayed silent.)

The kangaroo rat hopped away in an instant, but didn’t make it very far at all before collapsing. I would say the rat managed to make it maybe about 20 to 25 feet. It crossed the path in front of me and entered a foot-tall, meter-wide patch of diamond cholla (Cylindropuntia ramosissima) to my right and expired. The rat shuddered a few times and then laid still. The venom acted with extreme speed, killing the rat within 15 to 20 seconds at the longest. I hope it was painless, and given the tiny size of the rodent relative to the massive dose of venom it received it probably wasn’t too lingering a death.

Of course at this point I did not have any way to document the coming ecological interaction, so I departed the scene, went back to the house, grabbed the camera, and returned in less than three minutes. I wondered whether the snake would still be coiled under the buckhorn cholla, but I saw that it wasn’t and had come back into the open on the path within a few feet of where I’d originally seen it. It was hunting for its missing prey.

Unlike nonvenomous constrictor type snakes which kill their prey via suffocation and must tangle with their quarry intimately for quite awhile before they subdue it, rattlesnakes strike and retreat, allow the venom to do its deadly work, and then go in search of their prey, which generally won’t be very far away. They use their sense of smell to track the scent of their dying or dead target, sweeping their heads and upper bodies back and forth, flicking their tongues to capture scent molecules, and homing in on the location of their victim bit by bit.

I didn’t want the snake to find the dead rat in the diamond cholla clump, where clear photography would have been inhibited, so I picked up the rat by the tail and deposited it in the open in the middle of the driveway path. Readers can see the progression of the story from that point up until now in the photos above. I took multiple photos of the process of the snake zoning in on its quarry, inspecting it to find the head end, and starting to ingest it, but am only posting a few so as to avoid too much redundancy. I assume the snake would eventually have found the rat within the chollas or other dense vegetation, as this is something that must happen regularly, and if snakes couldn’t track their “slightly missing” prey a few meters then that wouldn’t bode well for their ability to survive. In any case I assisted because I wanted these photos, and because I didn’t want the rat to go to waste after the snake had expended energy and some of its venom supply on it.

In the photo above you can see the undulations in the snake’s neck and esophagus as it swallows the rat. Strong muscular contractions operating from both side to side and front to back enable these legless creatures to swallow their prey whole, since they are unable to tear it apart with teeth, beaks, or claws like most other predatory animals.

The snake has swallowed most of the hapless kangaroo rat, except for the long banner-like tail. Kangaroo rats have evolved these lengthy tails with brushed hairy tips as a tool that enables agility. By flexing their tails, which are as long as or longer than their main bodies, they are able to change direction extremely quickly, even in mid-air jumps, which is an ability that helps them escape predators like coyotes, gray foxes, owls, and yes, snakes a fair percentage of the time. Obviously not always however, as seen here….

The kangaroo rat is almost entirely consumed. You can see the bulge of the main body several inches down the snake’s esophagus while only a few of the black hairs at the tip of the tail remain. I wanted to offer the snake some dental floss to get the item stuck in its teeth out, but I probably would have been bitten, so I refrained.  Serpent oral hygiene is not my responsibility. 😉

A question crossed my mind as I photographed all this, and is doing so again as I write this post: Did I have anything to do with the snake’s successful hunt and the kangaroo rat’s death? I feel that inadvertently, I likely did. Obviously both snakes and kangaroo rats inhabit my Arizona desert property, and have for thousands or more years, and both species manage to successfully survive here without any human influences. But I suspect that the kangaroo rat was surprised and confused by my artificial light and distracted by the sound of me walking towards it (and the snake it never saw) a few seconds before the snake struck at it.

Kangaroo rats have extremely sensitive hearing and are quite capable of discerning even the subtlest slithering sounds as snakes move across the sand and gravel of the desert floor. This exquisitely acute hearing helps them survive since they hear the approach of many predators well before they arrive at the rat’s position. They also have lightning fast reflexes and adaptations such as the flexible long tail that enable last-second escapes. In return, rattlesnakes have evolved excellent camouflage, behavioral traits such as lying in wait for hours at a time in dead silence, and heat-sensing infrared facial pits to detect warm-blooded prey, all of which sometimes gain them an advantage in catching the nimble, cautious rats. In the ecological race between predators and prey, neither one always wins.

In any case, I do believe that it’s probable that by me being there, in the wrong place at the wrong time from the rat’s perspective, that I made it easier for the snake to make a successful strike. Mind you that I didn’t really have time to think about this at the time, as I had just found the snake in the beam of my headlamp only a few seconds before. I was some distance away (about 10-12 feet) and the kangaroo rat hopped into the picture just a couple of seconds before I could fully process what was happening, which was when the snake struck. Like I said earlier, I had just enough time to feel a flash of anxiety for the rat when the snake bit, and then it was too late.

This beings up a secondary question, which is, “Would I have acted to scare away the rat and save its life, had there been more time?”  The answer is probably not. After all, despite the rarity of my being present at just the right moment to witness it, this particular sequence of events is entirely within the realm of natural behavior and ecological balance. Like most ecologists and naturalists with a sense of how things operate in the natural world, I recognize that everything needs to eat, and while many people’s sympathies reside with the cute fuzzy mammal rather than the cold glassy-eyed reptile, my personal feelings are immaterial to the larger picture and drive for survival that has shaped both of these rather marvelously adapted species into what they are.

I will however admit that since I am human, I also cannot fully divorce some of my value judgments from situations like this. For example, had the snake been a critically rare species on the verge of extinction, I might want to make more of an effort to enable their survival by purposely breeding them and feeding them captive mice and rats (since kangaroo rats aren’t typically kept in captivity.) Or conversely, had the rat been rare and endangered, I might not want a relatively common snake capable of eating other prey to eat it, and I might had moved to intervene and save the imperiled rodent instead. But none of those factors were of concern in this case, and as such I just probably would have let the scene play out either way. Had the snake missed the rat, then that would have been interesting to see, but there would also have been nothing to document for this blog post either. So all in all, I suppose that I come down to the final analysis that I was privileged to witness and photographically document this since in 20 years I have not seen this play out before my very eyes.

Using the time and date stamp on my photo series, the entire process from the initial bite to this parting shot of the tail of the rattlesnake as it retires to digest underneath another cholla cactus, was about 15 minutes. The photos themselves show time stamps from 11:49 PM on Friday, August 3, 2018 to 11:59 PM just before the strike of midnight. If I allow for about 3 to 5 minutes for the time I spent watching the rat die and going to get my camera, we come up with a total time of slightly under 15 minutes. Just worth noting.

A small kangaroo rat is not a gigantic meal for a snake this size, and digestion will be fairly complete within 2 to 3 days and the snake will likely be out on the hunt again by later this week. Who knows, maybe I’ll be invited to the dinner party again?

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Addendum, Tuesday Aug 7, 2018: Thanks to some commentary and discussion on my Facebook page after I posted a photo and link to this blog post, I was made aware of some research being done by Dr. Rulon Clark at San Diego State University and a number of his graduate students regarding predator/prey interactions between several species of rattlesnake and the small mammals they prey upon. As I referenced above, there has been a very long history of ecological interaction between rattlesnakes and kangaroo rats (and ground squirrels and other small prey items.) Each one has developed ways to prevail at times through thousands of generations of trial and error on both sides, leading to some pretty intriguingly refined behavior. For the snakes, camouflage, silent ambushing, extremely fast striking speeds, and potent venom are all modes of trying to catch prey often enough to survive. For the rodents, exceptionally fast reflexes, behavioral displays, and resistance to the venom are all ways for them to escape or survive strike attempts. Less than 50% of strike attempts are successful, and days at a time may go by without even the opportunity for a strike, much less a successful one, so hunting is by no means a piece of cake for the snakes.

I have noticed in the past that kangaroo rats, which I see quite frequently at night while I work, show little fear of me in this remote rural area where no one ever lived before I moved here about 19 years ago. As such, they probably have not encountered a large bipedal primate before. Especially not one with a light source, which is entirely unfamiliar to them since the only natural sources of nocturnal illumination in the course of evolutionary history has been the relatively stationary moon, stars, and planets. (And I suppose flashes of lightning in the summer monsoon season.) So to encounter a human with a steady, yet rapidly moving light source is not within the purview of interpretation for a kangaroo rat, or a rattlesnake either, for that matter. They do not know what to make of it, and if I stand still and remain silent I often have the small rats hop right up to my boots, scuffling around in the desert sand for the seeds they feed upon. They show no fear if I don’t move. And even if I do move, they often dodge just a few feet away, and as long as I don’t actively pursue them they resume foraging.

But I discovered that if I make a sudden high-pitched noise, such as a click with my tongue as if I were disapproving of them, this sends the rats into flight mode. They frequently jump in the air, often in an unpredictable direction by flailing their tails, and leap several meters away. If I make several clicks at this point, they often just hop far away, determined to escape. My hypothesis is that an unexpected sharp sound of this nature has taught the rats that it could easily be the snapping of a twig underneath the foot of a coyote, gray fox, or bobcat, and it merits immediate evasive action. (Obviously snakes are not the only predators of kangaroo rats out here.)

As said earlier in the post, the desert is naturally a very quiet environment, kangaroo rats have extremely acute hearing, and anything that represents a potential threat in the audible range needs to be treated with instant concern and possible flight. But artificial lights do not have this effect because they are brand new factors in the desert night, one that kangaroo rats have not had time or need to work into their survival consideration. I believe that the lighting and my presence was the single largest factor that made the rat unable to perceive the threat of the snake until it was too late. It was distracted by me.

What I did not know, and one of the subjects of inquiry for Dr. Clark’s field  and laboratory research, is that kangaroo rats have evolved behaviors that signal to a rattlesnake that they are aware of to not bother striking, because despite the lightning fast movement of the snake in striking mode, the rat is actually faster and can dodge the snake if it has seen it and is ready to escape. Kangaroo rats will stomp their feet onto the desert soil to signal to the snake that they know it is there, and it also serves to warn other nearby rats of the danger and to be vigilant. This stomping is barely audible to human ears, but it is loud and clear to both the snake and the rats. Additionally, the rats often turn their backs to the coiled snake and kick sand in its face. Major disrespect! But it’s also an unmistakable signal to the snake that remaining here will be completely fruitless since everyone has been warned to watch out, so it may as well move along and try elsewhere. Snakes almost never bother to strike at rats that are foot stomping or sand kicking, because the prey is communicating clearly to the predator that they will not be caught tonight. Utterly fascinating!

Ground squirrels of various types are also primary prey items for rattlesnakes, but they are active during the daytime rather than at night. They, too, have evolved a series of behaviors and evasive maneuvers to avoid capture, including the same agility and immediate contorted leaping into the air response that kangaroo rats exhibit. But California ground squirrels (the main species of Dr. Clark’s research) have also developed ways to signal to the snake that they know about it and have warned others. This is something known as tail flagging, whereby the squirrel holds its long bushy tail upright over its back and waves it back and forth. This behavior clearly shows the snake that the squirrel is not going to be a target that day, and this combined with alarm calls and chittering shows other nearby squirrels that a snake is here, and to stay away. Again, snakes almost never bother to waste their time striking at a ground squirrel acting this way. In fact, the squirrels are so confident that they can avoid a snake bite that they often move to well within range of the deadly fangs, almost daring the snake to try a strike, taunting it, and knowing full well that they will dodge out of the way just in time.

Of course there are plenty of times that a given rodent of either species does NOT see the snake in time, does NOT display awareness signaling, and instead becomes a target. In my case above, I distinctly recall seeing the kangaroo rat wandering within range of the snake, presenting its body broadside to the reptile, and clearly mesmerized or confused by my light. Its attention was elsewhere (upon me) and for that error it paid the ultimate price. The snake reared up, hit the rat squarely on the side, and less than 20 seconds later it was all over for the rat. While in most cases a person with a light would not have been a factor, and snakes do successfully kill prey around 35 to 40 percent of the time when they do attempt a strike, in this instance I was probably the deciding factor in the snake’s favor and against the rat’s.

Despite the rat’s demise, I learned some very interesting new things about the snakes and the small mammals they often feed upon, and predator-prey signaling, which is a two-way communication between two antagonistic creatures with very different intentions in life outcome. Understanding how predators and prey communicate to each-other is quite important for various purposes, including species management in a world increasingly stressed by environmental concerns caused mainly by humanity in various ways. It is clear that in this communication process, that neither party always has the upper hand, or paw, or scales, or whatever tortured analogy you might want to make. 🙂

For a link to the San Diego State University web page that describes the research being done, visit this site:

http://www.bio.sdsu.edu/pub/clark/Site_3/Background.html

For some amazing YouTube videos of rattlesnakes interacting with both kangaroo rats and ground squirrels, including foot stomping, sand kicking, and tail-flagging (with a Robosquirrel!) here is the link to Dr. Rulon Clark’s video channel:

https://www.youtube.com/user/rulonclark

For one of the most-watched and amazing videos of a kangaroo rat narrowly avoiding death by a striking Mojave rattlesnake, check out this link: