If you have been following my rattlesnake study from the beginning, you know that we struggled through some faulty transmitters early in the project (search “failed transmitters” for previous info). The first six transmitters I implanted failed early. Several failed during hibernation (2014/15) and, because I knew where the snakes spent the winter, I was able to capture them when they began basking in the spring. Two, however, proved to be a bigger problem.
Male 36’s transmitter was first to fail in September 2014, with two months of activity remaining that season. Male 37’s transmitter lasted into the winter but he hibernated high on the bluff under a thick mat of vegetation, making his exact location very difficult to visit and impossible to pinpoint. Thus, both emerged in the spring of 2015 without functioning transmitters.
Both eluded recapture until October 2015, when I found Male 37 (details here) under the log I call “The Community Center” because everybody visits it from time to time. Males visit looking for girls, pregnant females hang out there to thermoregulate and give birth, and both sexes use it for shelter while waiting to shed (but nobody spends the winter there). I replaced Male 37’s transmitter then, leaving only Male 36 unaccounted for – until last week.
After twenty months, I had just about given up on finding Male 36 again. But when I checked around The Community Center one day last week, I was thrilled to spot his rattle with red/red paint! Like Male 37 last fall, Male 36 was also pre-shed and using The Community Center for shelter while he waited to complete the process.
Pre-shed Male 36, with failed transmitter, at The Community Center on 11 May 2016, moments before his recapture. If you look closely (partly obscured by grass), you can make out the new light-colored rattle segment forming under the skin at the rattle base.
Just like Male 37, I captured Male 36 and kept him several days until he shed. His transmitter was replaced and he was released yesterday.
Male 36 disappearing into The Community Center yesterday with a new transmitter and re-marked rattle (his rattle is quite long and likely to break soon, potentially taking his original paint with it). Note how clean and crisp his pattern appears after shedding, compared to the photo above.
The return of Male 36 fills my permit quota of seven telemetered males. We currently have five females telemetered and I am holding out, hoping to get a couple of females radio-tagged farther out in the northeastern portion of the preserve where few of our current snakes venture. Interestingly, Male 38 was hanging around with two females out there last week, including last Saturday when I was hosting a video crew from UC Santa Cruz. While I would have loved to get a transmitter into one of them, they were too wary and repeatedly escaped when approached.
I wish more people could see just how hard these fascinating creatures try to avoid confrontations with people!
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.
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!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: 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.
After being on the lam since December when his transmitter failed prematurely during hibernation, Male 37 was discovered getting ready to shed in one of his favorite hollow logs last Friday and recaptured. As soon as he sheds in a few days, his transmitter will be replaced and he will be released. Note in the photos below that this will be his 4th shed in 16 months (4 new rattle segments behind the paint); his new live segment is still covered by thin scales that will be lost with this shed. He has also lost five old segments from the end. He will be on display at our Living with Rattlesnakes booth at EYNC’s Nature Fest tomorrow, October 4th.
CROR 37’s rattle on 3 October 2015.CROR 37’s rattle on 14 June 2014.
As birthing season approaches, I have been watching intently for signs of baby rattlesnakes. While postpartum mothers usually stay inside their shelters, the neonates are typically active and easily spotted. Although they do not leave their shelters before shedding the first time, babies can usually be seen crawling or basking at the entrance. And when we introduce the BurrowCam into the shelter, the kids can be seen exploring their new surroundings and crawling around on their mother. So far, there’s been no evidence of babies yet this year. This would be a bit early but quick warming last spring has me wondering about the potential for early births this year.
Remember that pregnant female rattlesnakes in our area hangout in carefully selected thermal shelters where they can maintain consistently warm body temperatures around the clock until they give birth. This period of thermoregulation lasts several months, during which the pregnant moms do not forage for food.
All five of our telemetered females are apparently pregnant, plus Female 55, who was processed and released without a transmitter in June (no transmitter surgery due to some old but significant trauma to her abdomen; click here for details). These females settled into their gestation shelters between 8 June and 1 July and have maintained body temperatures between 28ºC and 32ºC (82º–90ºF), almost without exception, ever since.
In fact, at dawn on a recent cool morning (16 August) when the ground temperature just before sunrise was in the mid-50s F, these girls still had body temps in the high 80s F. They maintain similar body temps during hot afternoons when the ground temperature (much hotter in the sun than air temp) outside is 120ºF and more. They thermoregulate like this by selecting logs or large rocks that have just the right thickness and sun exposure to stay warm at night but not get too hot in the afternoon sun. Such places are apparently scarce because three of our telemetered females are together in one shelter, while Female 41 is with non-telemetered Female 55 in another. Female 54 is in a third location, possibly by herself, but there could be others in there without radios. Females 39 and 41, both of whom produced broods in 2014, are in the same shelters as last year.
Flash photo of Female 41, tucked into her gestation refuge at sunrise on 16 August 2015. Note in the inset how her scales are pulled apart by her developing brood. Female 55 is also in this shelter but not visible on this morning.
On 27 August, the BurrowCam revealed Female 39’s abdomen to be greatly distended, extending all the way to the cloaca. So maybe delivery of her 2015 brood is not far off? The frame grab (below) from the BurrowCam video shows her abdominal scales pulled far apart. In the 50-second video (watch here), you’ll see what I see when we thread the BurrowCam into a passage. Female 39 is identified by red/blue (red-over-blue) paint in her rattle and the edge of another dark gray rattlesnake appears to be visible under 39’s coils. Known to be behind her in the passage (because of their radio signals) are Females 47 and 53, as well as Male 46. Additionally, in recent days, I have seen non-telemetered (and non-pregnant) Female 48 (green/green) and Male 36 (red/red; carrying a failed transmitter) in this log. It’s a popular place this time of year!
Frame grab from a 27 August BurrowCam video showing the distended abdomen of telemetered Female 39, deep in her gestation refuge.
As you may recall, Males 36 and 37 have been missing for months since their transmitters failed prematurely in September and December, respectively. Until last week, Male 36 had been last seen on the BurrowCam in a hollow log courting postpartum Female 41 on 2 October 2014, and I last saw Male 37 as his tail disappeared down a hole on 7 March 2015. There had been no sign of either of them since until a fellow photographer and herpetologist I encounter frequently at Effie Yeaw showed me a photo of Male 37 (IDed by his yellow/red rattle marking) crossing a trail on 20 August! Then, just 5 days later, while checking for babies in the shelter with Females 39, 47 and 54, and Male 46, I was surprised to see Male 36’s red/red rattle. (See photos below) So both are alive and well… but both still elude recapture.
Male36 (red/red paint in rattle) deep inside a hollow log with Female 41 on 02 October 2014.
Male 36 inside another hollow log on 25 August 2015 with at least three pregnant females and a smaller male. Compared to the 2 October photo (above), note that he has two additional rattle segments between the paint and the live black segment, indicating he has shed twice in the past ten months.
Earlier today, 29 August, I found Male 46 coiled in poison oak dozens of meters away from the log where he has been hanging out with the three pregnant girls continuously for the past two weeks. It is likely he has been chased off by a larger male, so maybe Male 36 is still in there. This refuge has a narrow deep passage that is nearly impossible to thread the BurrowCam into and, even when successful, I can usually only see whichever rattlesnake is closest to the top (for example, the 50-second video of Female 39, with the link earlier in this post).
So Baby Watch continues and I still hope to recapture missing Males 36 and 37.
Good news: On 25 April, I came across our Female 39, who’s transmitter had failed prematurely 19 days before. She was captured, her transmitter was surgically replaced, and she was released the next day. At her initial capture last July, she weighed 365 grams (12.9 oz) and she produced a litter of kids a couple of months later. When recaptured last weekend, she weighed 404 grams! She clearly has been hunting successfully and is in great shape to reproduce again this year. While tropical pit vipers often reproduce annually, pit vipers in temperate climates like ours often require a year or two to replenish body fat before they can sustain another pregnancy.
But annual births are not unheard of this far north. In fact, we had a female rattlesnake produce litters three years in a row in El Dorado County a few years ago. After her third litter, however, she was skin and bones and we didn’t think she would survive the winter. But she did and might have pulled through if she had not been nailed by a raptor the following spring.
One day we found her radio signal to be weak and coming from far down a canyon, well outside her typical home range. Because thick manzanita and chamise made getting to her signal very difficult, I didn’t investigate right away. Eventually, when her signal didn’t change, we burrowed through the chaparral until we got to a large live oak that stood by itself on a hillside. The snake’s transmitter was laying in the leaves under the tree, completely clean and undamaged – as if it had been surgically removed and washed! I have had telemetered rattlesnakes eaten by coyotes before but coyotes chew the transmitters. The undamaged transmitter under a lone large tree far from the snake’s last location just screamed raptor. The area was full of red-tailed hawks and there were certainly owls at night.
Back to our current study, just two males, 36 and 37, remain loose with failed transmitters. I recently shipped the other five faulty transmitters back to the manufacturer for evaluation and repair.
Last week I found one of the hollow logs frequently used by our telemetered rattlesnakes freshly ripped apart (photo below).
I’m not sure what kind of animal, besides a person or a black bear, might have ripped a log apart like that. While it is certainly not impossible for a bear to stray this far downstream, it would also be attracting attention in more obvious ways. Having encountered a visitor with a snake hook off-trail a few weeks ago, I thought this might be a good time to reiterate why I am no longer publishing plots of the study animals’ travels (as I did last year) or providing more details about where they are hanging out. Too many rattlesnake researchers have had study animals captured or killed after they disclosed their locations.
But I do want to share how far the telemetered rattlesnakes have been roaming during the first six weeks of the season. The illustration below shows the home ranges used by the seven rattlesnakes with working transmitters so far this year. The solid lines are the males and dashed lines are the females. The Effie Yeaw visitor center is in the top center and the EYNC parking lot is in the top left corner of the Google Earth photo.
The most interesting finding to me is that Females 41 and 47 have been moving as much as any of the males and much farther than some. Also remember that we lost almost three weeks’ movement on Female 39 when her transmitter failed. Male 35 had a small home range last year, primarily because he hung around in the elderberry and redbud thicket next to the bike rack for so much of the summer. He spent most of the rest of his time in the meadow – and that’s where he is again. Male 40 was the last to leave his winter shelter this spring, has not moved as frequently as the other males, and I have not found him courting any females. He has always been quite under weight for his length. He is an old guy, based on his untapered rattle and an impressive collection of scars, but he seems to be getting by.
Courtship seems to have slowed a bit in the past week, with most animals by themselves and apparently hunting, at least when I have visited. Nonetheless, there should be another month or so of courtship before the summer hiatus.
The little male courting Female 47 in the video I posted on 4 April continued to court her until at least 11 April, staying with her a total of 9 days that I observed. During that time, the female made several short moves of just a few meters and I never observed any indication that she did anything but ignore the male. Presuming that she was trying to hunt (these rattlesnakes are predominantly sit-and-wait ambush predators), it is hard to imagine that she could have had much success with his nearly constant movement. Despite my best efforts, the little male evaded several attempts to catch him. On two occasions, I actually had him but was unable to get him into a bag before he wiggled loose and disappeared into thick grass. On both occasions, I was sure I had spooked him and he would abandon the female but he didn’t. He only became more wary and would vanish instantly the moment he detected my approach. Since I have enough photographs to identify him in the future, I have given him the next identification number: CROR51.
Then on 13 April, I found that Female 47 had made a 97 m (318 feet) move out into the meadow. When I located her, she was under a mat of old dry grass beneath the living grass. I did not find Male 51 with her but, because I had to dig around in the grass to find her, he certainly had time to flee unobserved. She was in the same spot with no other snake observed on 15 April, too. On 17 April, she had moved 58 m southeast, back into the edge of the forest. She was coiled in the grass, apparently hunting and alone.
Today, 19 April, she had moved only a couple of meters. But as I got close to her signal, a rattlesnake shot out of the grass near my feet and under a nearby log – Male51! When I actually found Female 47, she was about 5 m from where I had flushed Male 51 and I saw why Male 51 was not with her. She was being vigorously courted by Male 49, a much larger male that was processed and released in early March without a transmitter. In fact, Male 49 had courted this female between 22–26 March at another location 150 m away. You can see the value of marking the rattles with paint in the photo from today (below), Female 47’s rattle is marked with yellow/green paint and Male 49 is marked with white/green. Since Male 49 is not telemetered, he would not be identifiable without the paint in his rattle.
Sadly, Female 39’s radio signal disappeared on 3 April. Of the six animals implanted with that batch of refurbished transmitters, five failed early. I have found and replaced transmitters in three of them, Males 35, 38 and 40. At present, Males 36 and 37 and Female 39 are carrying transmitters with prematurely dead batteries. I am still hoping to either find them courting or being courted by telemetered snakes or to have them turn up around the buildings or Maidu Village where staff can capture them.
Now that we have accumulated some data this spring with three females that are not incubating late-term embryos, I can demonstrate more effectively a behavior I mentioned last year. During the last 2–3 months of pregnancy (generally about mid-July to October), females find shelters where they can thermoregulate to stay within a narrow body temperature range. That is, they need a shelter that keeps them warm at night but where they are protected from the midday heat. I have repeated the chart from last year below on the left, showing the body temperatures of two late-term pregnant females compared to the males. The chart on the right is corresponding data from this spring, comparing body temperatures of non-gestating females with the males.
In these charts, “frequency” is the percentage of observations where I recorded each body temperature for that sex during that period. In 2014, the average male body temp was 24C (75F) while the female average was 30C (86F). This spring, males have averaged 24C (75F) and females 22C (72F). Of course, the weather is cooler in the spring (even this spring) than in summer but there is ample opportunity for these snakes to get their body temperatures up above 30C (by late morning, ground surface temperatures are often above 40C in direct sunlight, even when air temps are relatively cool). But my point is that there is no real difference between average male and female body temperatures before the pregnant females go into their late-term thermoregulatory behavior… which is evident in the late summer data above where body temps of the pregnant females narrowly cluster around 30C (86F).
(For you statisticians that may read this, I admit that these data are not publishable in this form as they contain some significant pseudoreplication. Nonetheless, they serve to illustrate my point that gestating vs non-gestating female body temps are very different.)
Hopefully, we will get a few more females telemetered in the next month or so and, by mid summer, we should know if any are going to reproduce this season.
We now have a total of 14 rattlesnakes marked at Effie Yeaw Nature Center, including 9 males and 5 females. This spring, I have processed, marked, and released 3 males and 2 females without transmitters (mostly too small for the transmitters). With prematurely failed transmitters in Males 36 and 37, we currently have working transmitters in 4 males (35, 38, 40 & 46) and 3 females (39, 41 & 47).
You almost need a scorecard to keep track of who has been with who over the past couple of weeks. Lots of the action has occurred at a small hollow log where Female 41 spent the last month or so of her winter slumber by herself. She departed on 13/14 March and just five days later Female 47 turned up there with Males 38 and 46. The three snakes were coiled next to and touching each other on 19 March in a narrow bit of shade. The late morning sun was hot and all three body temperatures were elevated (female = 86F and males = 91F & 93F), indicating they had recently been in the sun. The female disappeared into the log when I approached but the males were more concerned about each other than me. The smaller male, 46, was still excited and head-jerking (a common part of rattlesnake courtship) a little bit. Each time he would touch Male 38, the larger male would shove him away, pushing violently by thrusting a coil sideways. Male 46 would push back, reminding me of two brothers in the back seat on a long car ride. I suspect I may have missed some male combat earlier, which was probably cut short as their body temperatures approached dangerous levels and they were forced to get out of the sun. (Click here to see a video of male combat, shot in front of the EYNC Visitor Center in 2010)
Also on 19 March, Female 41 was found (by herself, as far as I could tell) in the refuge where Female 39 delivered her kids last year.
On 21 March, Female 47 and Male 38 were were still at the small hollow log, although laying a few inches apart and not actively courting when I was there. Male 46 was by himself several dozen meters away in the grass. At 674 mm (26.5 inches) snout-vent length, Male 46 was no match for Male 38, who measured 821 mm (32.3 inches) SVL at his recent transmitter replacement surgery. As you can see from the video mentioned above, male combat is a wrestling match and larger body size is a definite advantage. Snout-vent length or SVL is the common way biologists record body length in lizards and snakes; the tail is usually measured separately.
On 21 March, Female 41 had left the birthing refuge used by 39 last year and was coiled by herself under a pile of dry live oak branches. The following day, she had been joined by Male 46 and the two were copulating at about 11:20 AM. In the photo (below), Male 46’s rattle colors are green/red and Female 41’s are white/blue, although the blue is difficult to see through the brush.
Also on 22 March, Female 47 was still at the small hollow log but Male 38 had been replaced by Male 49, who was actively head-jerking, chin-rubbing, and tongue-flicking the female. Male 49 is not telemetered (but recognizable by white/green paint in his rattle) and at 767 mm SVL, he is not quite as long as Male 38, but he outweighs Male 38 by 28 grams (377 g vs. 349 g), Of course, I have no way of knowing if 38 and 49 even crossed paths; Male 38 could have departed before Male 49 arrived.
On 23 March, Female 41 had moved back to the birthing refuge used by Female 39 last year and had apparently been followed by Male 46; they were still together there on 24 March, although they were basking about 4 feet apart when I visited on both dates.
Female 47 was laying partly in the sun on the morning of 23 March with Male 49 nowhere in sight. Of course, without a transmitter, I had no way to find him. But they were laying together in the same place again on the next two mornings, so I suspect he was there on the 23rd, just not visible.
Female 41 remained at 39’s old birthing refuge on 25 and 26 March. Male 46 was still there on the 25th but they had been joined by Male 38. On this day, Female 41 and Male 46 were again basking apart from each other and male 38 was out of sight, betrayed only by his radio signal. The next day, 26 March, the female was basking, Male 38 was there but out of sight, and Male 46 was alone in a poison oak thicket some distance away.
By 27 March, Female 47 had left the small hollow log where she had been for nine days (with 3 males at various times) but she had been replaced by Female 41, leaving Male 38 apparently alone where he had been with Female 41 for the previous couple of days. As far as I could tell, Female 41 was also alone.
Also on the 27th, Male 35 was found a few minutes after 11 AM eating a California vole (aka meadow mouse, Microtus californicus) in thick knee-high grass next to the main trail, not far from the picnic area. The snake stopped swallowing and we were lucky that he did not spit out the rodent when he was disturbed, as rattlesnakes are quite defenseless with their mouth stretched around a meal. George Nyberg and I had to remain motionless for many minutes before the snake finally decided it was safe to continue swallowing. We shot a few photos as he finished his vole.
On the 28th, all of the telemetered snakes were coiled in vegetation, alone, and apparently hunting. Both places where most of the courtship had occurred over the past two weeks were empty. Are they finished courting? I doubt it; it’s not even April yet!
The day after I saw Male 37 in the flat woodland (7 March), down from his winter shelter on the hillside, Male 38 was found about 10 meters (33 ft) from his hibernaculum, where he remained coiled in the grass for several days while basking when possible. Although other telemetered rattlesnakes remained at their winter shelters for most of last week, they were often found basking in the sun, as were several unmarked rattlesnakes.
I caught and marked several of those new basking rattlers and, as it appeared that another cold snap was unlikely, I implanted transmitters in CROR46, captured on 6 March, and in a new female, CROR47, captured a few days later. I could not palpate any fetuses in Female 47 and I don’t think she is pregnant but it’s possible, as it is very early in the year.
As of today, Female 41, who produced kids last season and apparently hibernated by herself, was coiled in deep green grass about 30 yards from where she spent the winter (below), apparently hunting. Male 35 was coiled in deep grass under a live oak tree he frequented last year. He’s the one who spent so much time in the vegetation near the bike rack, silently welcoming guests much of last summer. We’ll see where he goes next.
You may remember that Male 40’s transmitter was the most recent to fail prematurely. Well, I was able to recapture him today. I also recaptured Male 38, who’s transmitter is still working but is part of the batch that have been failing early. Both will be released with new transmitters in the next day or two. Males 36 and 37 remain on the loose with failed transmitters.
Finally, Male 46 and Female 47 have found each other and were laying in the sun together this afternoon (below). There was no active courtship when I saw them (they were very still) but I’m not buying that this is a platonic relationship this time of year!
As you can see from the photos, these rattlesnakes are almost impossible to see in the thick carpet of green grass that covers the park now. And when approached too closely, they disappear silently into the grass – as Female 47 did as soon as I tried to get closer after the photo above. Of course, the green grass makes it very easy to step on a rattlesnake!
As of today, Female 39 is the only telemetered animal that has not left her winter shelter, although her body temp has been warm (indicating she has been basking, although I haven’t seen her) and, several days ago, she moved to the other end of the log where the location of her radio signal was identical to that of Male 35 for a couple of days before he left. Hmmm…!
I also heard two different California ground squirrels incessantly chirping their alarm call this afternoon. When they are signaling a hawk or coyote, they usually chirp once or twice and dive for cover. When they continue to chirp over and over, it is often a snake (unlike a hawk or coyote, once they discover a snake, they can avoid it without going underground). Unfortunately, I didn’t have time to investigate today.
On February 26, I came across another unidentified young adult rattlesnake at the refuge where so many others appear to have spent the winter. He or she was basking in the sun but escaped into the refuge, showing me in the process an unbroken rattle of about 7 segments with no paint. No time for photos, either. No other snakes were found basking that day.
I found Male 38 and Female 41 basking in the late afternoon on both 1 March and 3 March. Their body temperatures were 70F & 86F, respectively, on 3/1 and 84F & 90F on 3/3.
On the afternoon of 6 March, Female 41’s body temperature of 86F indicated she had been basking earlier but she was out of sight when I looked for her. By comparison, body temps for animals that have not basked recently have been around 10-14C (50-57F). While I did not find any of the marked snakes visible on 6 March, I did find a new male basking and captured him – CROR46. He has an unbroken rattle of 8 segments, making him relatively young but, at 264 g (9.3 oz), he is a good candidate for a transmitter. I will have to research the extended weather forecast for our area and if another cold snap looks unlikely, he will get a transmitter. I will also photograph his face and compare him to the unmarked snake photographed at this refuge on 14 February.
Just after 10 AM today (7 March) I found Female 41’s radio signal (her transmitter is not from the problem batch) rapidly increasing in pulse frequency, indicating she was cool but warming rapidly in the sun. Unlike some of the other basking rattlesnakes in the area, I have never found her basking in the open, out from under cover; she only exposes a small part of her surface area to direct sun while remaining sheltered. Take a look at the photo below and note how little of her was in the sun, yet her body temperature increased from 48F to 59F as I monitored it over just 20 minutes!
Finally, I spent some time around midday today checking some the favorite places for Males 36 and 37 – both are carrying dead transmitters. Surprisingly, I came across an adult rattlesnake at the base of the hill where both hung out last year. The snake was only partly exposed, with head and anterior body already in a hole and its tail hidden in the grass. Just as quickly as I saw it, it continued down the hole but not before I could clearly make out Male 37’s yellow/red rattle markings. Although I couldn’t capture him (without tearing up the environment, which I won’t do), he was 32 m (105 ft) from his winter refuge high on the hillside… so spring emergence is definitely underway! I have been told by several other people of recent rattlesnake sightings but this is the first of our study animals to be found away from his hibernaculum this year.
Little has changed over the past ten days; fence lizards basking midday when it’s sunny but no rattlesnakes out when I have checked. The only interesting development was on 19 February, when I found that Female 41 had moved again, this time about 7 m (23 ft) to another smaller log where she was out of sight.
Today, I started collecting data on my Droid smartphone, rather than taking paper notes. Using a program called iFormBuilder, I have been able to create a menu that allows me to record twenty-nine observations of things like where a snake is, what it’s doing, temperatures, other environmental data, nearby flora, etc., mostly by making choices on drop-down menus. When I’m done, it automatically up-links to my computer at home where the data is waiting to be saved in an Excel spreadsheet. This not only helps standardize the data I collect but it saves an unbelievable amount of time by eliminating the need to manually enter data from paper notes. I used a similar system during my 40-month field study of Mohave rattlesnakes (2001-2004) and recorded something like 150,000 data points during more than 3700 encounters with the snakes; if that had been done on paper, I would still be working on data entry!
At 12:17 PM, I found a small unmarked male rattlesnake laying in the sun at the same refuge shared by CRORs 35, 38, 39, 40 and several others. He was captured (CROR45) and processed. At 242 grams (9 oz), he is large enough for a transmitter (the rule is the transmitter should not exceed 5% of the snake’s body mass, so my 9 g transmitters require a snake of 180 g (6 oz) or larger), however, releasing him with a fresh surgery when the weather is likely to be cold for weeks to come is not good. Physiological processes in ectotherms (animals that rely on the environment for body heat rather than making their own) slow way down when they get cool, which includes their immune systems and their ability to heal wounds. So Male #45 will be processed (measured, marked, etc.) and released where he was captured without a transmitter.
Before releasing him, however, I wanted to see if he was the same snake I saw on 14 February, since his body size and rattle looked very similar. But after comparing a photo of his face with my photo of the unidentified snake from 14 Feb, I found that they are not the same animal. In the photos below, note the difference in shape of the margin of the postnasal scale at (1), the speckling pattern of the preocular scale at (2), and the shape just under the eye of the margin of the dark postocular stripe at (3). Of course, there are many other dissimilarities in the photos… bottom line, it’s not the same animal.
The last development to report from 24 February is that I could not get a radio signal from Male #40. Thinking that he might have left the refuge with all the warm sunny days, I walked around for awhile without detecting his signal, so I returned to the refuge and used the burrow camera to look for him. Sure enough, there he was (yellow/blue paint in his rattle). This is the third transmitter to fail prematurely and all are from the same batch of refurbished units (they last a year and, after removal from the snake, are returned to the manufacturer to be rebuilt with new batteries). As I have mentioned previously, the manufacturer very rarely gets a bad lot of batteries which then affects an entire series of their transmitters. The good news is that I have no more of that batch of transmitters. The bad news: CRORs 35, 38, and 39 all have those transmitters in them. Transmitters have already failed in 36, 37, and now 40. Hopefully, I can catch Male #40 basking and catch him before he leaves the refuge – which could be any time, given the unseasonably warm days. I am reminded that one of those transmitters functioned for over a year in the last telemetered rattlesnake at my El Dorado Hills study site, so maybe all of them don’t contain bad batteries. Nonetheless, I will replace the transmitters in 35, 38, and 39 as soon as they leave their winter refuge, rather than waiting for their normal 12-month replacement.
