The first thing I encountered early in the afternoon of 13 May was a dead adult rattlesnake in the grass behind the Visitor Center. The carcass had completely putrefied and had been eviscerated by insects. It was an average-sized adult and had no paint in its rattle (i.e., it was not one of our study animals). I could not determine the sex. The head and rattle were intact, indicating it was unlikely a human had killed it. There was no obvious evidence of trauma elsewhere, either, but it was in such bad shape that it was difficult to tell. People often ask about the life expectancy of rattlesnakes and the answer is that, in captivity, they have been known to live more than 30 years. But in the wild, if they make it to adulthood (which few do), they are constantly threatened by raptors, coyotes, kingsnakes, people and their cars, temperature extremes, and other hazards. My guess is that few make it to ten years.
About 3 PM on the same day (13 May), I found the radio signal from Female 41 coming from dry grass on the hillside near the stairs on the trail behind the amphitheater. When I refined her location and parted the grass, I found her swallowing a small rodent – which she immediately spit out (this is common defensive behavior, as rattlesnakes are defenseless when swallowing prey). I had to remain completely still for five minutes or more before she decided it was safe to eat again. Because she was so deep in the grass and I had only a small opening through which to view her (photo below), I could not tell exactly what kind of mammal she was eating. It was uniformly gray with very fine fur, a gray belly, and was about mouse-sized. It was too large for a shrew and the lack of a light-colored belly ruled out most native mice. The dorsal fur looked too fine for a vole and I could not see the tail. What I could see looked like a house mouse, Mus musculus, but we will never know for sure as I did not want to bother her further and be the cause of her abandoning her kill.
When I next visited her two days later, she had moved only a few feet and was coiled next to a California Ground Squirrel burrow, which she retreated into when I arrived. This was the first time this season I have found a rattlesnake close to or in a ground squirrel burrow. I haven’t seen ground squirrel pups yet but I saw a pregnant female on 11 May, so I suspect there are pups in burrows by now and the rattlesnakes hunt the pups heavily in spring and early summer. (Click here and scroll to the bottom of the first page for more info on the fascinating interaction between Northern Pacific Rattlesnakes and California Ground Squirrels)
With all of our telemetered rattlesnakes alone and apparently hunting (and not having found a courting pair since 20 April), I was beginning to wonder if courtship might have concluded early this spring. But on 16 May, I found Male 38 on top of an unmarked female next to the large log in the meadow. She was heavy, healthy, and had no paint in her rattle – a beautiful rattlesnake, but she was also quick! As so often happens, the courting male was far less afraid of me (too much testosterone?!?!) than the female, who fled immediately and made it under the log before I could capture her.
I wish that people who fear rattlesnakes and think they are so malevolent could see how these animals really react to being approached by a person. If I had been able to catch all the unmarked rattlesnakes that have escaped from me this spring, our quota of seven males and seven females with transmitters would be full… but they are shy and very quick to flee into the grass, wanting nothing to do with something as big as a person. Remember, in their tiny primitive brains, rattlesnakes react to encounters based on three criteria: Can it eat me? Can I eat it? Can I mate with it? Clearly, we fall into the first category!
On 19 May, I found Female 47 in the meadow a little after 10 AM, crawling slowly through the grass, carefully tongue-flicking as she moved. I took a few photos and she crawled out of sight while I recorded my standard data. But when I started to depart, I came across her a couple of meters away with an alligator lizard, Elgaria multicarinata, in her mouth. She retreated a short distance to a small shrub with the lizard still in her mouth and, after I stood motionless once again for several minutes, she began to swallowed it (photo below).
Two days later, while searching for Male 35 on 21 May, his signal led me to a large and very dense thicket of armpit-high Milk Thistle (Silybum marianum) in the meadow. I have avoided penetrating this thicket when various males have occasionally visited it this spring because the spines go right through all clothing and there is just no way to avoid them. But on this cool morning, when I peered over the thistle into a little clearing in the thicket, I saw a nice unmarked rattlesnake laying in the grass, probably hoping the clouds would clear and allow some sun to shine through (photo below).
Hoping that she was a “she” and probably the reason that Male 35 was also in the thicket, I carefully retreated without spooking her and dropped all my gear in the grass except a cloth bag and snake hook. Stepping into the sea of spines, I slipped the snake hook under her and began to gently lift her before she reacted. I almost got her clear of the thistles before she wriggled off the hook but I was able to quickly catch her again before she completed her escape. Once clear of the thistles and in the dry yellow grass, she could no longer hide and I had her in the bag shortly thereafter.
Her sex was later confirmed and she became CROR53. (Click here for an explanation of CROR). She was very heavy for her length and full of shiny white abdominal fat when I implanted the transmitter. I could not be sure of her reproductive condition because of so much material in her bowel; she clearly had been feeding very successfully. Reproductive condition is determined by palpating her belly through her belly scales, feeling for yolk masses and, later in the season, for embryos. Because the transmitter incision is less than 3/4 of an inch long and made on the side, two scale rows up from the end of the belly scutes, it doesn’t help in determining reproductive condition. When she was released the morning after her surgery, she became our fourth telemetered female, along with four telemetered males (plus two additional males with failed transmitters I am still hoping to recapture). I am up to 413 recorded encounters with EYNC rattlesnakes this year… we are off to a great start!
Soon to come: an explanation of shedding and rattle growth.