A death mystery and rattlesnake season winding down

Male 37

Our wayward male shed on the morning of 7 October, five days after being recaptured. His faulty transmitter was surgically replaced that afternoon and he was released the following morning.

CROR37 recovering from anesthesia on 07 October 2015. Original Droid IMG_20151007_162411334.jpg
Male 37 recovering from anesthesia on a heated pad after his transmitter surgery on 7 October. He now measures 969 mm (just over 38″) total length, making him the largest rattlesnake I have measured at Effie Yeaw. Besides shedding four times in the past 16 months, his body mass has increased 26% (now 668 g or 1.5 lbs.), while his length increased by almost 5%. This is a very healthy rattlesnake!
CROR38 at release on 08 October 2015 Original RAW IMG_9094.CR2
Male 37 on the morning of 8 October, disappearing into the hollow log where he was captured. Note that I marked his rattle again, since his original paint is only two segments away from being lost.

 

I took advantage of the necessity to allow Male 37 to shed before his surgery to collect some useful data. His pre-shed body mass was 693.5 g. By weighing him again and subtracting his post-shed mass of 668.4 g, we find that he lost 25.1 g (0.9 oz.), which was 3.6% of his body mass. Then, by drying his shed “skin” on a hot plate to drive off ambient moisture and subtracting that mass (5.1 g) from 25.1g, we can calculate that 80% of the mass he lost was water. Although these rattlesnakes are unaffected by California’s drought so far (more details here and here), that will eventually change and such data will be invaluable for calculating water loss and gain over time (water “flux”) and predicting when the snakes will become water stressed.

More Mortality

Another healthy postpartum female, CROR 47, was killed on the morning of 21 September. I may have been premature in assuming that a coyote killed Female 54 on 14 September (details). Female 47 was also very fresh when I found her, killed in the early morning in the meadow by something that did not eat her.

Death scene: CROR47 in meadow of Effie Yeaw Nature Preserve, morning of 21 September 2015 Original RAW IMG_8736.CR2
Death scene: Female 47 in the meadow at Effie Yeaw Nature Preserve on the morning of 21 September. The posterior end of her abdomen was laying a few feet away. The edge of the bright red transmitter can be seen in the grass near the middle of the photo. Clearly, the carnivorous yellow jacket wasps found her quickly.

It was obvious that Female 47 had been pulled apart, with her body in two large pieces and internal organs and strips of skin pulled away. But she was all there. Maybe most interesting was the condition of her head: The top of her head was intact and unmarked but her lower jaw was mostly gone and the roof of her mouth was mangled, especially where the fangs had been (caution: graphic close-up).

In reconsidering the death of Female 54 a week before, I assumed that her missing head and neck had been eaten but it is entirely possible that I just didn’t find them. And I rationalized that a coyote dropped the snake as it probably fled (unseen) from me. But I see coyotes around the meadow frequently and, while they give people a wide birth, they are not panicked by our presence. If I interrupted a coyote with Female 54, why wouldn’t it have carried the rattlesnake away to finish the meal?

So what would encounter both rattlesnakes in the meadow early in the morning and pull them apart before leaving them uneaten? I have had coyotes kill Mohave rattlesnakes in southern California in the past but they eat the entire snake and chew the transmitters; these transmitters were undamaged. And what would remove the jaw and mangle the inside of the mouth?

My best idea is turkeys. Interestingly, I have found nothing in the scientific literature about wild turkeys killing adult rattlesnakes, although there are several anecdotal accounts in books, including Laurence Klauber’s Rattlesnakes (1972, Univ. California Press) of turkeys mobbing adult rattlers. Inquiries of my rattlesnake researcher colleagues has produced one witnessed account of a wild turkey killing and eating a two-foot timber rattlesnake (Crotalus horridus) in Minnesota. And there is a video on YouTube of two turkeys apparently killing what appears to be a large gopher snake (Pituophis) on a golf course.

If anyone reading this has first-hand information about wild turkeys interacting with rattlesnakes, I would love to hear about it.

2015 Season almost over?

Well, it’s the last week in October and our eight telemetered rattlesnakes appear to be mostly settled into their winter shelters, despite relatively warm weather. Last year, we still had three telemetered rattlesnakes roaming around well into November (see my “Rattlesnake Update” from 26 November 2014).

This year, one of our telemetered animals has been stationary since 16 September and others have stopped moving since 6 October, 12 October (2 animals), and potentially three more in just the past couple of days. Most interesting of all is that five of them are in the same shelters they used last year – and a sixth may be on his way. This is a departure from behavior observed during my field work in El Dorado County, where the rattlesnakes did not return to the same locations winter-after-winter, although some returned to previously used sites after spending a winter or two in other locations.

This year at Effie Yeaw, our skinny geriatric Male 40 went immobile on 16 September under the same log he shared with Males 35 and 38 and Female 39 last winter. Then Male 35 and Female 39 joined him, arriving on 6 October and 12 October, respectively – although their radio signals indicate that they are not together under the large log. Male 38 is still on the move, even visiting the residents along Edgehill Lane three days ago (26 October). I was unable to gain access to his location due to the necessary residents apparently being away and, when I returned yesterday, I found that he had returned to the hillside within the nature preserve. Male 37 spent a few days in the same area on Edgehill Lane in August 2014 and also returned to the preserve before I could gain access to him. These are the only two times (in two full seasons) that telemetered animals have entered the residential area on the bluff. When this occurs, I try to contact the property owners and would remove the snake, if that’s the property owner’s desire and the snake is accessible. In both cases, however, the rattlesnakes  returned to the preserve before I could make contact with the necessary residents. But back to Male 38, he was on the hillside yesterday morning and may be headed back to last year’s log with the others.

Male 37 went directly to the hillside after I released him with a new transmitter on 8 October and I have not detected a change in the location of his radio signal since 12 October – which sounds like the same place he spent last winter (again, refer to my “Rattlesnake Update” from 26 November 2014). Once I’m sure he’s down for the winter, I’ll make the treacherous climb and verify his exact location.

Female 41 arrived on 20 October at the log where she spent last winter. She moved a few meters away over a couple of days but has been back for the past three days, so she may also be done for this season. As far as I could determine last winter, she was alone. Male 46 and Female 53, neither of which were telemetered last winter (i.e., I don’t know where they spent last winter), are very close together under another large log and have been there for at least three days.

It is interesting to note that the rattlesnakes that are already in their winter shelters are not basking, preferring to remain out of sight with body temperatures mostly in the 60–65F range. Earlier in the activity season, when cool nights are followed by warm morning sun, the rattlesnakes come out and warm up by exposing some or all of their skin area, depending on ambient temperature and the intensity of the solar radiation. But in ectotherms (animals that get their body heat from the environment) like rattlesnakes, body temperature varies with the environment and both metabolic rate and water flux increase with higher body temperature, burning more stored energy and using more water. So, on the verge of four or five months of hibernation, the rattlesnakes are likely programmed by evolution to cool off and slow their metabolism, thereby conserving energy and water for use in the spring.

Once I’m sure the snakes are done moving for the year, I’ll summarize the season’s findings in the context of last year’s data and our original questions and study goals.

 

Life and death among the rattlesnakes

You may remember from my last post that pregnant Female 53 had made a surprising move of more than 220 yards near the end of August and was discovered, apparently by herself, in a small burrow at the edge of the river bottom. Interestingly, after monitoring her there for a week, she turned up back in the original refuge on 8 September. Although I have not been able to get a look at her with the BurrowCam, the burrow she was in for a week is empty and I have no reason to believe that she’s not still pregnant.

Then, last Thursday (September 10), I found three significant developments when I visited this same birthing refuge occupied by expecting Females 39, 47 and 53. First, Female 39 was gone, with a distant weak radio signal. Second, I finally got a direct look at some babies – either three of them or the same one three times, crawling around inside the refuge (photo below)! Interestingly, the one(s) I saw had shed; they were brightly marked and their little two-lobed rattle buttons were uncovered. That, of course, means that they were around 10–14 days old and ready to leave. And, third, one of the visible adults was jerking and chin-rubbing on Female 47 – sure signs of a courting male (click here for a courtship video). This guy had no paint in his rattle, so he’s new but he was inaccessible inside the shelter. But the fall portion of the courtship season has definitely begun.

A post-shed young-of-the-year crawling over an unidentified adult inside RFG01EY on 10 September 2015. Original RAW IMG_8590.CR2.
A post-shed youngster crawling over an unidentified adult rattlesnake in its birth shelter on 10 September 2015.

Female 39 was already postpartum, so her departure was not surprising. But her offspring should have left (or be leaving) at the same time. The post-shed kid(s) I saw could have been her’s or Female 47’s. When I tracked down Female 39’s radio signal, she was in the blackberry thicket on the other side of San Lorenzo Way, laying in diffuse sunlight and sporting a very recent food bulge (just behind the U-shaped bend in her neck in the photo, below). Interestingly, this annually-reproducing female had her babies in the same refuge last year and, when she departed, she immediately made the same long move to the same spot in the same berry thicket – on 15 September 2014. Apparently this is the best place to find a good meal when you finally get the kids out of the house!

Recently postpartum female Northern Pacific Rattlesnake (CROR39) with recent food bolus, basking on 10 September 2015 near Effie Yeaw Nature Center. Original RAW IMG_8606.CR2.
Recently postpartum female Female 39 with recent food bolus, basking on 10 September 2015.

 

As of the morning of 14 September, all females except 53 had left their gestation shelters. I came across Female 47 crawling in the grass, so I maneuvered in front of her and shot some video as she crawled toward me. Although I remained motionless, I think she detected me as she got within two or three feet, because she started carrying a slight “S” bend in her neck, which I interpret as a defensive precaution in case she needed to strike and bite (when not feeling threatened, they usually extend the neck when crawling, as in the first half of the video). I was accidentally kneeling almost on top of a ground squirrel burrow and she dove into it when she found it. Click here to see the 28-second video.

A short time later, I found that Female 54 had also departed from her gestation refuge but had made it only a few dozen meters. Her partly eaten carcass was laying in the edge of a trail just a few feet from where an adult turkey had been killed and eaten a couple of weeks ago. Her blood had not yet coagulated and the exposed tissue was still moist and glistening. In recent weeks, I’ve frequently seen one or two of the now almost grown coyote pups in this area and there has been coyote scat everywhere. I have no doubt that one of them got her.

Female CROR54 partly eaten, morning of 14 September 2015. Blood is not coagulated and exposed tissue is moist and glistening. Original Droid IMG_20150914_094119031.jpg
Female 54, partly eaten on the morning of 14 September. I suspect a coyote was having her for breakfast when I approached and interrupted his meal.

Then, at the shelter used for the past couple of months by Females 39, 47 and 53 – and still occupied by 53, I came across a freshly shed youngster a couple of feet outside of his birth refuge.

Two-week-old youngster just emerged from his birth refuge, 1 m behind him. Original IMG_20150914_164416116.jpg
A two-week-old rattlesnake, less than a foot long, that had just emerged from his birth refuge. He (or she) was contemplating the big unknown and dangerous world for the first time.

 

Assuming that Female 53 delivers a brood soon, our six monitored females will probably have contributed nearly 50 baby rattlesnakes to Effie Yeaw’s Nature Preserve (average litter size is 8). But remember that, on average over time in a stable population, a female rattlesnake (or any other species) only produces a replacement for herself and a mate in her lifetime that survive to reproduce themselves. Otherwise, the population increases or decreases.

A kingsnake visits a birthing refuge occupied by two pregnant rattlesnakes
Captured by a time-lapse camera, this kingsnake was checking out a gestation refuge occupied by two pregnant rattlesnakes in September 2011, during my El Dorado Hills study. Both females gave birth within the following week. Baby rattlesnakes are just hors d’oeuvres for kingsnakes, which probably know very well where the rattlesnakes give birth and they may well eat a large percentage of newborn rattlesnakes.

 

The vast majority of offspring never live long enough to pass on their genes. Of course, there are cycles between predator and prey species. When predator numbers are up, they soon knock the prey population down, which eventually results in a reduction of predators as food becomes scarce. Then, as predator numbers decline, the prey population begins to increase again… and the saga continues. Remember what I’ve said before: it’s a violent world out there and Nature is a cruel mother; most wild creatures’ lives end in the jaws of another!

 

More feeding, courting, and a new female

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.

adult female Crotalus oreganus (CROR41, in situ) swallowing an unidentified rodent (Mus or Microtis) at Effie Yeaw Nature Center on 13 May 2015 Original RAW ING_7074.CR2

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).

Female Northern Pacific Rattlesnake (Crotalus oreganus; CROR47; in situ) eating Southern Alligator Lizard (Elgaria multicarinata) at Effie Yeaw Nature Center on 19 May 2015. Original RAW IMG_7254.CR2.

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).

CROR53 in situ at capture site. Original RAW IMG_7320.CR2

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.