On Monday, 7 September, I found Female 53 missing from the hollow log where she had been gestating with Female 39, who was still present. This is the hollow log where I photographed a new baby on 6 September (see my last post) and I could glimpse youngsters deep inside the log again on the 7th. After considerable searching, I detected 53’s radio signal and followed it to a sycamore tree near the edge of the American River, 368 meters (402 yards) from where she had been. Since that day, she has moved a hundred meters or so back toward the oak woodland but has settled into a small cavity in the rocky riverbed.
This morning, 15 September, I found multiple shed “skins” from babies back at the hollow log and Female 39 was gone. I had checked the log yesterday and found no neonatal sheds.
Female 39’s radio signal led me to her 195 meters away, where she was coiled in dappled sun with lots of loose skin hanging on her. The babies shedding over the past 20 hours and the departure of Female 39 confirms that the kids were hers and were only a day or two old when discovered on 6 September (about 11 days between birth and the postpartum shed). Inspection of the inside of the log today with the BurrowCam revealed no rattlesnakes.
Then, when I checked Female 53 in her rocky riverbed hole this morning, she no longer appeared pregnant. In the BurrowCam video (link after the still photos below), look closely beyond her, just right of the center of the frame (next to the snail), beginning about 41 seconds into the clip. For the next 8 seconds, you can see a shiny wet baby moving behind her! I have circled the place to look in this still frame:
Also, compare the appearance of her abdomen in today’s video to her 3 September photo (in my last post).
Today’s 60-second BurrowCam video can be viewed on YouTube (click here).
Meanwhile, Female 75 remains in her burrow, still without kids, while Female 80 is still high on the bluff and inaccessible.
I have mentioned before that much research has been done on the interactions, both behavioral and biochemical, between Northern Pacific Rattlesnakes (Crotalus oreganus) and California Ground Squirrels (Otospermophilus beecheyi). And that research continues.
It started, so far as I know, with studies by UC Davis psychology professors Donald Owings and Richard Coss in the 1970’s, when they became interested in how California Ground Squirrels behaved when confronted by Northern Pacific Rattlesnakes. Several researchers have since spun off various aspects of the relationship between these two species, including Dr. Rulon Clark and his students at San Diego State University, who study the phenomenon from the rattlesnakes’ perspective. A common thread among these studies is that the adult squirrels are largely resistant to the rattlesnakes’ venom, often surviving with nothing but a nasty wound that eventually heals (although adult squirrels occasionally succumb, vividly illustrated by the photo accompanying the Washington Post article linked below).
But while adult ground squirrels seldom die from rattlesnake bites, their pups are much more vulnerable and the rattlesnakes hunt them intensely, starting about this time of year. I have linked a 60-second video made by Denise and I in July 2014 of our Male 36 (yes, the same one just recaptured after 20 months) preying on a ground squirrel pup while the pup’s mother tries to defend her offspring (Read original account here).
Tail-flagging and pushing grass at the snake are common behaviors by adult California Ground Squirrels when confronted by rattlesnakes. In this one-minute clip, the snake had already bitten a pup, which is laying in the grass and out of the frame at the start. The adult squirrel soon retreats to the stricken pup, which appears as a dark area in the grass. The adult squirrel’s attempts to deter the rattlesnake appear to work momentarily a couple of times as the snake turns away but almost immediately comes back toward the bitten pup. Near the end of the clip, the snake reaches the pup and bites it again. Although the pup runs out of the frame, it only makes it a few feet. The rattlesnake follows and swallows it a few minutes later. Excuse the background helicopter noise, as the fire department was conducting an operation in the river nearby. View the video here.
I bring this up now because my friend, videographer George Nyberg (who produced the very nice 2015 video of my rattlesnake study), has alerted me to a new Washington Post article on the biochemical “arms race” between Northern Pacific Rattlesnakes and California Ground Squirrels (view article). Thanks, George!
Matt Holding, whose research is the focus of the WP piece, is a former graduate student of another friend, Dr. Emily Taylor at Cal Poly San Luis Obispo. Jim Biardi, second author on the new study, is a former member of the UC Davis group that originally studied ground squirrels and rattlesnakes.
The Washington Post does a nice job of describing how natural selection works: in short, there is always variation among individuals and some are better adapted than others to feed themselves (or avoid being eaten!) and those individuals tend to survive longer and produce more offspring, which carry the genes for those successful traits. Less successful traits are passed on less frequently (i.e., fewer offspring are produced). The peer-reviewed paper upon which the WP article is based was published in the journal Proceedings of the Royal Society B (volume 283, issue 1829, April 2016). However, since this is not an open source journal, access to the complete manuscript is not easily available to the general public right away.
How well do rattlesnakes tolerate surgically-implanted transmitters?
As I have discussed before, there is a long (20+ years) history of telemetry studies of rattlesnakes in which individual animals tolerate the transmitters for years, enduring periodic surgeries to replace the radios. The animals thrive, repeatedly producing offspring and growing at the same rate as rattlesnakes without transmitters.
I bring this up because of a phone call last weekend from the landowner where I conducted my El Dorado County field study. He had just encountered the first Northern Pacific Rattlesnake I ever marked and telemetered, still identifiable by the yellow-over-yellow paint remaining in his rattle. He is now an exceptionally large male with twelve rattle segments – but in 2009, he was a young animal with a tapered unbroken rattle. He eventually endured four annual surgeries to implant and replace transmitters, followed by a fifth surgery in 2013 to remove his last radio.
Male 01 being sighted alive and healthy is just more evidence that the surgical protocol and other study methods used by me and many of my rattlesnake-researcher colleagues is well tolerated by the animals we seek to learn more about.
Despite my frequent admonition that we often tend to give rattlesnakes and similar animals too much credit for cognitive thought, friends at San Diego State University recently published some compelling evidence that rattlesnakes may learn from experience and apply those lessons to anticipate and mitigate problems during future similar circumstances. Bree Putman and Rulon Clark have spent years studying rattlesnake predation tactics by setting up video cameras on hunting rattlesnakes and recording their predatory encounters with small mammals. (This works because rattlesnakes are ambush hunters that sit still for long periods of time, waiting for prey to wander by.)
While reviewing 2000 hours of video, Bree and Rulon discovered two examples of rattlesnakes using their heads and necks to move foliage out of the way that might otherwise interfere with a strike when prey wanders close (click here for video). The animals involved were Northern Pacific Rattlesnakes – the same species as we have in the Sacramento area. Similar behavior has been reported a couple of times in the past, once involving a Prairie Rattlesnake (Crotalus viridis) and once involving an Arizona Blacktail Rattlesnake (Crotalus molossus); both these incidents were witnessed by observers but not recorded.
Thus, evidence continues to accumulate that rattlesnakes are likely more social and maybe more intelligent than previously thought – although many habits are undoubtedly genetically programmed by natural selection. The new report by Putman and Clark is contained in the current issue of The Southwestern Naturalist (volume 60, number 4; December 2015).
I’ve been getting lots of questions after last night’s (17 April) KCRA News interview with a local “rattlesnake hunter” who makes his living keeping us all safe from rattlers. If you have been reading my blog, you know there is nothing new to be alarmed about. The last few hot days have not brought out the rattlesnakes. Indeed, general emergence from their winter dens occurred more than a month ago. Male rattlesnakes continue to be busy looking for and trying to mate with as many females as they can while the females hunt for mice, rats, and other prey. As sit-and-wait ambush predators, the females don’t move much and thus are seldom encountered by people. But the males have been and will continue to constantly search for females until late May or June, in the process turning up in yards and on trails and other places where they encounter people.
Once again, most bites can be avoided by watching where you put your unprotected hands and feet and leaving rattlesnakes alone when you encounter them.
We have been encountering numerous pairs of rattlesnakes in the Effie Yeaw Nature Preserve over the last few weeks. Here are brief video clips of a couple of examples: First, our telemetered Male 62 (blue/white paint in rattle), entwined with an unmarked female. These snakes were not moving during my brief visit but the males often accompany the females for many days but cannot keep courting them continuously (click here for video). You can see why in the video of Male 37 actively courting Female 41… it takes a lot of energy! (click here).
On 1 April, several hours after I videoed Male 37 courting Female 41, I returned and just missed a fight between two males over Female 41. As I approached, I briefly saw both males, with heads and necks high off the ground, twisted around one another. But one quickly fled, either from me or he had had enough of Male 37…who is a big healthy male rattlesnake! In any event, Male 37 was all excited and remained raised off the ground for a minute or more, guarding his girl (see photo below).
A video made a few years ago of two males fighting on the concrete in front of the Effie Yeaw Visitor Center doors is on the Nature Center website (or click here to see it).
Despite persistent cool mornings and alternating sunny and cloudy days, nine of eleven telemetered rattlesnakes have left their winter shelters and the remaining two have been basking regularly and will undoubtedly be on the move soon. We have also been finding plenty of new rattlesnakes basking and now have 27 animals processed and marked with colored paint in the rattles, in addition to the eleven with radios.
As I have already described, Female 41 was one of the first to leave her hibernation site and was soon joined by Male 49, a snake marked last season but not telemetered. Male 49 and Female 41 remained in close proximity at the same location from 16 February until 20 March and, although they were occasionally coiled in contact with one another, I never saw the male courting her. Male 49 followed when Female 41 moved more than 50 meters between 20 and 24 March but there has still been no witnessed courtship. However, the grass is very thick at their new location, making her hard to see and him impossible to spot if he’s not with her (and I don’t want to step on him… they’re very fragile!).
On 22 March, I came across Female 55, another animal processed last year and released without a transmitter, basking alone at the edge of a large log. But when I returned on 24 March, she had company: an unmarked (no paint in the rattle) male on top of her, jerking, chin-rubbing, and tongue-flicking – typical courtship behavior (you can view a 2015 clip of Female 41 with another male here).
We can expect the females to hunt for the next two-to-three months, after which pregnant females will retreat to their favorite gestation shelters to thermoregulate until their kids are born around the first of September. Non-pregnant females will continue to hunt through the summer. Males will spend most of their time looking for receptive females until late May/early June, after which they, too, will hunt full-time for voles and ground squirrel pups until courtship resumes in late summer.
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.
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!
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.
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.
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.
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!
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.
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!
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.
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.
Yesterday, 3 April, I found an unmarked rattlesnake with a very short broken rattle on top of our Female 47. The unmarked snake fled immediately but I was able to see that he was a small adult with only two rattle segments (the live proximal segment plus one hollow one). As there is no reason for another female to be accompanying Female 47, I almost certainly interrupted a courting male.
When I returned today, Female 47 had moved about 6 m and the same unmarked snake was on top of her. Since I approached with more caution today, I was able to watch and video tape the courtship. The female appears to have been in a typical round “pancake” coil and looks to be completely unresponsive; she does not move except for being pushed around by the male. The male, on the other hand, goes through a cycle of 30-90 seconds of rest followed by a short period of head and body jerking, short rapid tongue-flicks and chin-rubbing on the female, culminating with pushing his cloaca around under her. During this process, you will see the male wag his tail. The male then goes back into a rest phase before repeating the effort.
This is very typical rattlesnake courtship behavior. Since the cloaca (on both sexes) is sealed by a flat tight-fitting belly scale, courtship by the male is almost certainly wasted effort unless the female is receptive. What makes her receptive? Can he woo her into being receptive? We are not sure. Head-jerking, tongue-flicking and chin-rubbing is energetically expensive for the male and the movement exposes both snakes to potential predation, so it must be productive or the behavior would not endure. And the female is almost certainly selective, maybe selecting mates based on size, health, courtship performance, or other criteria. How long the male can keep up the courtship may be an indication to the female of stamina and health.
Female health, particularly replenishing body fat since delivering her last litter, may affect the female’s receptivity but fertilization of ova does not necessarily coincide with copulation. Long-term sperm storage is well established in many pit vipers, including rattlesnakes. Thus, it is common for a female rattlesnake to store viable sperm for multiple seasons, allowing her to fertilize ova without having recently mated. But does that mean that a female will mate when she is not physically ready to produce young? At this point, we just don’t know how all of this works.
In the video, the male’s head is at the top of the frame and his tail is in the lower left. The female’s head is in the lower right. So, click here for a 45-second clip of today’s courtship.