Last week I was wandering my property a bit after sunset, inspecting the gardens for anything that needed watering or maintenance. It was not yet dark but the sun had gone down about 20 minutes before, and the gathering early June dusk meant that extra caution is merited since this is when rattlesnakes might be active. Since I do not kill rattlers and have decided to coexist with them, I’ve learned to just be vigilant since they are pretty well-camouflaged and you can have an accidentally close encounter with one before you know it. These unintentional interactions are usually because the snake decided not to rattle – without the auditory warning, it is easy to walk only a few feet away from a snake coiled under the bushes without ever even seeing it. Which is fine…. just as long as you don’t step within striking distance, there’s no danger to being more than a few feet away of a rattlesnake whether you are aware of it or not.

Many rattlesnakes don’t actually rattle if you approach, especially not if they don’t perceive you as a threat and believe that you are going to pass them by without seeing them. From the snake’s perspective, rattling comes with a cost – the cost of being noticed, which is riskier than being unnoticed, because certain animals (would be predators, nasty-tempered human primates) might actually take action against the snake that could prove fatal. Despite their venom and their dangerous reputation, rattlesnakes are actually quite vulnerable to large animals and occupy a space that is at best in the middle of the food chain. Plenty of animals will make a meal of a rattler if they are able to, and of course many humans kill them on sight even when they aren’t a real threat, so in general rattlers tend to prefer to wait quietly for prey and avoid confrontations with animals larger than themselves.

Thus I was a bit surprised when I heard the characteristic buzzing sound of a snake about 12 feet away from me. I had not even noticed it hanging out underneath a wolfberry shrub (Lycium pallidum) in the fading light, and was not on a trajectory of crossing its path either, so had the snake chosen to remain silent, I would not have even known about it.

Of course I was interested in the snake and wanted to observe what it was doing, so I diverged from my originally intended path to inspect the scene. I found that it was probably a western diamondback (Crotalus atrox) and that it had captured and killed a cactus wren (Campylorhynchus brunneicapillus) which it was preparing to consume. I don’t know why the snake felt it necessary to rattle and alert me when I wasn’t very close to it, but not every snake has the same temperament or level of threat sensitivity. Whatever the snake’s “logic” was, I now knew about it.

I did not have my camera at the time, but I went back to the house to get it and returned within 5 to 6 minutes to document whatever was going to happen. I hoped that I could capture a series of photos of a wild snake ingesting a cactus wren, but that’s not always possible since sometimes your presence disturbs a snake enough to cause it to abandon its prey. I’ve had that happen before with a gopher snake (Pituophis catenifer) that had caught a baby rabbit but as soon as I came across it by accident, the gopher snake abandoned the rabbit and fled down a nearby rodent hole. I was sorry for having disturbed its meal, even though it was random chance and not malice, and I hoped that the rattler would be more amenable to having an audience as it had dinner.

Well clearly, as readers can see by now, the rattler decided that I wasn’t going to interrupt its meal. I took up a station sitting on the ground about 6 or 7 feet away from the serpent and used a telephoto zoom lens plus a flash to get all the photos you’re seeing here. When I first happened upon the scene, alerted by the snake itself, the dead cactus wren was several feet away from its killer. This is a common thing for venomous snakes to do: Bite the prey, retreat, and wait at a slight distance while the prey dies. By not entangling with struggling prey, the snakes lower the risks of injury to themselves. And while small prey such as a cactus wren is unlikely to actually cause a snake any harm, it’s still a sound survival strategy and explains why the bird was not already in the snake’s grasp.

By the time I retrieved the camera and got back to the wolfberry shrub where this was happening, the rattlesnake had coiled around the dead bird and was apparently preparing to swallow it. As you can see in the photos above, the snake braced the dead wren against its body, rotated it so that it would be eaten head first, and started to ingest it. Once started, the snake repositioned itself and the wren into more of a straight line, which would enable a smoother process of engulfing it.

While a cactus wren is not a particularly ambitious meal for a rattler of this size (about 28 inches / 70 cm long) to swallow or digest, it is worth noting that the bird’s body is still several times the diameter of the snake’s head and neck. Swallowing anything several times larger than your neck without chewing it or cutting it into pieces therefore takes time, and snakes are in a rather vulnerable position while they do this. The snake is under a certain amount of physical stress, and is unable to bite in self-defense during the time that it is swallowing the prey, so this might be why many snakes will not attempt to eat something while there is a large onlooker present. Obviously this is not always the case, and captive snakes habituated to people learn to get over this reticence, but to see this behavior in the wild is rather uncommon.

Note how far the snake’s skin has stretched out. In the process of consuming their prey whole, most snakes have a lower jaw that can unhinge and elastic skin that can expand 4 to 6 times its normal width to accommodate the necessary act of eating.

The swallowing process took this particular diamondback rattler about 10 minutes from start to finish. Obviously the hardest part is at the beginning, before the bird is mostly consumed and the snake’s body has dilated to the point where it can accommodate the meal. The narrowest point of a rattler’s anatomy is the relatively thin neck located right behind the triangular-shaped head, which has to stretch to about 6 or 8 times its normal size for several minutes while the bird carcass passes. Once most of the bird is inside, the final act of swallowing into the larger stomach cavity is fairly quick. Note how the neck scales are massively distended when compared to the first photo where the snake hasn’t started ingesting the bird yet. It’s pretty amazing when you carefully consider it!

I waited a few more minutes after the swallowing process was complete to see and photograph the lump of the bird’s body migrating down the snake’s esophagus and into the stomach, where it will reside for at least several days as it undergoes the digestion process. I would have caught a few more photos, but unfortunately the snake was now mobile again and starting to retire deeper into the sheltering shrubbery, making decent photos difficult, not to mention the fact that by now it was almost fully dark.

While the snake’s esophagus is visibly distended, the diameter of this thicker part of its anatomy is maybe only half that of the bird’s body, and it must feel much less uncomfortable for the snake. Obviously there are size limits to what any given snake can swallow, and a cactus wren as stated above isn’t a particularly enormous meal, unlike an adult cottontail rabbit for example, or in the case of certain snake species other snakes as large as they themselves are.

I find it interesting to ponder the digestive process than a snake has to go through as well. By swallowing prey whole and intact, this rattler has just consumed a large proportion of inedible material, including feathers, bones, and claws. Of course snakes have evolved ways to handle this issue, which includes potent digestive enzymes that dissolve bones, and the ability to regurgitate pellets of hair and feathers that might not be digested by the end of the process. I did a little research into how snakes digest their prey, and found an interesting article in The Daily Mail from the UK which had x-ray photographs of a Burmese python digesting an alligator almost fully within 7 days. I’ll add that link below.

http://www.dailymail.co.uk/sciencetech/article-3058837/Reptile-death-match-X-rays-reveal-Burmese-python-devouring-alligator-body-digests-sharp-toothed-prey.html

Thanks for reading!