The first of our four pregnant rattlesnakes has given birth since last Thursday (between September 8 and 12).
The animated GIF file above shows Female 54 in the foreground inside a hollow log and still pregnant (note the scales pulled apart on her abdomen) but with babies crawling over her on both sides. Female 39 is in the background and no longer pregnant. Since these are the only two females I have seen gestating in this hollow log this year, I believe the kids belong to Female 39. The video was recorded with our BurrowCam, actually a Ridgid Tools inspection camera that can be inserted up to three feet into burrows, logs and other narrow chambers.
As you know if you have been reading this blog for very long, mom and babies stay together for a week or a little longer, until the kids shed the corneal layer of their skin for the first time. After that, they go their separate ways to forage for food before hibernation. Thus, if my telemetered females are in sync with the larger population, baby rattlesnakes should begin appearing on the trails around the fourth week in September.
This is Female 39’s third brood in four years. Each time she has reproduced since I have been monitoring her, she has made a beeline to the same spot in the blackberry thicket on the other side of San Lorenzo Way as soon as the kids leave home. Apparently fall rodent hunting is very good there! We’ll see if she stays true to form this season.
I’ve been getting this question a lot lately. And my response is, “It depends on where you are.”
Actually, it depends on the local weather in recent years where the question is being asked.
Many of the female rattlesnakes in the Effie Yeaw Nature Center preserve have been reproducing annually since at least 2014, including the drought years prior to this extraordinarily wet winter and spring. And, as I have written here before, that’s unusual – at least according to similar studies of other species of North American rattlesnakes. This far from the equator, most pitvipers only produce a brood every two or three years because of the time it takes females to replenish sufficient fat stores to support another pregnancy (they lose 30-50% of their body weight with each litter). But along the American River Parkway during 2014, 2015, and 2016, there was enough local rain each winter to get the annual plants growing and everything blooming, providing plenty of food for insects, squirrels, voles, and other small animals. The insects fed the abundant lizards that reproduced like crazy each year, and the rattlesnakes fed on the small mammals and lizards that were plentiful. So rattlesnakes and other mesopredators (mid-level predators in the food chain; i.e. they are eaten by bigger predators) have been thriving locally, despite the historically low reservoir levels and skimpy snowpack in recent years. And because rattlesnakes produce only one brood per year, they can’t do better than they’ve been doing.
On the other hand, when local drought reduces the availability of the rattlesnakes’ prey (i.e., reduced local rainfall significantly suppresses plant growth, which negatively affects everything else up the food chain), that changes the snakes’ behavior. Among other things, movement and courtship slows significantly and reproductive rates are almost certainly reduced.
So, in an area like the American River Parkway, this wet spring is not likely to increase the rattlesnake population because they can’t reproduce much better than before all the rain. However, in areas where reduced rainfall in recent years significantly impaired floral growth , rattlesnakes will be better fed and more active this year and they are more likely to successfully produce young.
But it is important to understand that what people interpret as “abundance” is usually just a change in behavior. I studied this phenomenon in Mohave rattlesnakes in the southern California desert for my MS thesis. In dry conditions, predators get most of their water from the body water of their prey (we’re all about 70% water). So, when rodents are abundant, rattlesnakes are well hydrated, behave normally, and males search constantly for females during spring and fall. But when their prey becomes scarce and other water sources are not available, they reduce water loss by remaining coiled and moving less, thus reducing the amount of skin exposed to the dry air. This is important because cutaneous (through the skin) evaporation accounts for about 75% of the snakes’ daily water loss.
As a result, during local drought, people encounter rattlesnakes less frequently – not because there are fewer rattlesnakes but because they remain hidden and move around a lot less (top photo, below). During non-drought times, people see more rattlesnakes because their behavior is not inhibited and they crawl around a lot more (bottom photo, below), especially the males during their courtship season.
So, if you live in an area like the American River Parkway, where there has been lush growth of grasses and other annual and perennial plants in recent years, this wet year should make little difference in the apparent abundance of rattlesnakes.
But if your neighborhood has been dry with little springtime plant growth in the last few years, you may see an increase in rattlesnakes this year for two reasons: the males may be searching for females much more than before, plus there may be more baby rattlesnakes in September and October this year (and likely next) as a result of females having plenty of rodents to eat this year.
First, I have added a link on the main menu to a new video (UC Santa Cruz Video). Bethany Augliere and Brendan Bane from the UC Santa Cruz Science Communication Program visited the EYNC Rattlesnake Study last May and recently posted the resulting video, which satisfies one of the requirements for their graduate degree program. I hope you enjoy it!
Back to baby rattlesnakes
As of 22 September, all three telemetered reproductive females (39, 53 and 75) had left their birthing shelters. Two are clearly hunting and the third is just a few feet away, being courted by a male.
Female 39 produced a brood in the same hollow log for the third year in a row. Then, immediately following the kids’ neonatal sheds on 14–15 September, she made a long move to the same place in the blackberry thicket on the other side of San Lorenzo Way – also for the third year in a row. As I observed last year, she apparently knows where to find a reliable meal after the kids leave the house!
Female 75 abandoned the ground squirrel burrow she had been in for weeks between 17 and 19 September and moved to a blackberry thicket near the Duck Pond. Although I never observed babies in the burrow with her, the tunnel was deep and she was sometimes out of sight of my three-foot-long Burrow Camera. After she left, however, a single neonatal shed “skin” was visible in the burrow and I recovered it yesterday. Hopefully, DNA from it will confirm that Female 75 produced a litter and reveal who the father was. Since multiple paternity is common in rattlesnake broods, the DNA from this skin will not identify the paternity of any other siblings.
Female 53 left her shelter in the stream bed between 19 and 22 September, moving only about 4 meters to another shelter where she is accompanied by a non-telemetered male, CROR 72 (green/yellow paint in his rattle). Note the postpartum skin fold in the frame shot (below) and then watch the brief video of the two rattlesnakes together. (click here)
The underground void that Female 53 just left remains occupied by an unmarked female with babies. You can see fresh neonate skins on top of and stuck to this female and it is difficult to tell if the kids in the video have shed yet. I suspect the recently shed skins belong to Female 53’s litter which has already departed and the remaining babies belong to the unmarked female. If I am right, these babies will remain with mom for a few days more. However, if the fresh sheds belong to them, they and their mother will be gone the next time I visit. It is important to remember that maternal accompaniment of neonate rattlesnakes has only been known since radiotelemetry has been used to study these animals. Watch the video here.
So it appears that the 2016 birthing season is nearly complete. People around the American River Parkway and other places where rattlesnakes live will be encountering baby rattlesnakes with some frequency between now and the onset of cold weather. But, at the size of pencils, the little guys have many predators and few of them survive until spring.
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.
Just a quick post to let you know that as of last Saturday, 3 September, Females 39, 53 and 75 were all still visibly pregnant.
But yesterday afternoon, 6 September, a newborn baby was coiled in the hollow log where 39 and 53 had been on Saturday. I could not see the adults well enough to tell which one had given birth. There were undoubtedly other kids that were not visible. Since the neonates start a shed (ecdysis) cycle almost immediately after birth, which turns their eyes bluish-white, this one’s clear eyes indicate he is not very old.
As of Saturday, I could not see neonates in the burrow with Female 75.
Since my last post, I also came across the first Fall courtship. Early on 29 August, I came across an unmarked male courting Female 66, who is not pregnant this year and has been hunting all summer. A couple hours later, the apparently happy pair were copulating! Remember, these rattlesnakes have a bimodal courtship season: they court in the Spring, lay low during the hot months, and resume courtship in late Summer/Fall.
Well, we are entering that time of the season when we can expect to find baby rattlesnakes any day now. Of course, the youngsters will not be roaming around where they might encounter people for about 10-14 days after birth…so we usually don’t encounter them on trails and in yards until early September.
But our six telemetered females are displaying a variety of behaviors indicating that all may not be about to produce babies. Six weeks ago I reported that Females 39, 41, and 53 were all pregnant and in the gestation shelters they have used repeatedly to thermoregulate before giving birth in previous years. Furthermore, I could feel six fetuses in Female 80’s belly when I implanted her transmitter in June.
Since that mid-July report, Females 39 and 53 have behaved predictably for expecting moms, remaining in their gestation shelter, and both appear to be about to produce kids. In the photos below, note the abdominal girth of these females, with scales pulled widely apart.
This will be the third consecutive year that Female 39 has produced offspring and the second for Female 53, so far as we know. We were not monitoring them previously. Between the first of July and yesterday, 23 August, the average body temps for Females 39 and 53 have been 28C (82F) and 29C (84F), respectively.
Six weeks ago, Female 41 had just returned to the gestation shelter she used the previous two years, which led me to believe she was likely pregnant again. However, after staying only three weeks, she left and has been spending her days mostly out of sight in various ground squirrel burrows during August. I have not been able to get a good look at her in recent weeks but her behavior and average body temperature of 26C (79F) suggest that she may not reproduce this year. Although Female 41 produced kids in both 2014 and 2015, I want to remind readers that skipping a year or two between broods is far more common than annual reproduction for temperate-latitude pitvipers.
Our remaining three telemetered females are new to the study this year, so I have no data from previous years. Female 66 has behaved quite normally for a non-reproductive year: hunting continuously throughout the spring and summer. Her July-August average body temp has been 22C (72F).
Female 75, however, appears ready to produce babies, although she has been moving back and forth frequently between two ground squirrel burrows 17 meters (56 feet) apart. Her average body temperature during July and August has been 27C (81F).
Finally, there is Female 80. When I captured her and implanted her transmitter in June, I could clearly feel six fetuses lined up in her abdomen. Shortly after I released her at her capture site near the base of the bluff, she climbed up the hillside and has remained near the top ever since. On three occasions, I have climbed that steep, loose, and treacherous slope but have failed to locate her. Her radio signal seems to emanate from thick ornamental ivy growing down from a residential backyard under fig and valley oak trees. She is also just above an underground wasp nest. Just to be clear, I am far more comfortable with rattlesnakes than a nest of wasps – especially where I cannot easily run away! Since I have no previous data from her, she could be in her usual gestation shelter. However, her July-August body temperatures are not consistent with a gestating female, with an average of 23C (73F). I’m not sure how this is going to play out…
Just for comparison, the seven telemetered males have been moving around a lot, hunting and occasionally hanging out with the pregnant girls for a day or two at a time. Their average July-August body temps range from 17C (63F) to 26C (79F), with the average between the boys of 23C (73F). Note how closely these data match non-reproductive Female 66’s average body temp of 22C (72F) during the same period.
That’s it for now. Next post will almost certainly be (cute!?!?) baby pics!
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!
Just when you think you are beginning to understand rattlesnake behavior, they do something completely unexpected. But, of course, that’s exactly why we study them!
Compared to my previous observations of Northern Pacific Rattlesnakes, this year’s mothers and neonates are behaving very differently. For starters, during multiple seasons at my El Dorado Hills study site and last year at Effie Yeaw NC, newborn rattlesnakes basked in the entrance to their birth shelter, usually in the morning, with mom laying just behind them. With a stealthy approach, they were not difficult to photograph.
As of yesterday (6 September), 5 of 6 monitored females had had their babies but I have yet to actually lay my eyes on a youngster. The only images of kids so far this year are from videos made underground with the BurrowCam. In one case, Female 54 has been so far into a void under a large log that even the four-foot probe of the BurrowCam just reveals empty tunnel as far as the light illuminates. Yet, yesterday morning, she was outside for the first time in weeks and clearly no longer pregnant (photo below). Her kids are nowhere to be seen.
Two weeks ago, the radio signal from our Female 53, who had been stationary with two other pregnant females for over a month, disappeared. After searching for her for several days, I finally caught a faint signal and followed it more than 200 m (220 yards) to a small burrow in the soil where the BurrowCam revealed that she was alive and still pregnant. As of yesterday, she was still there and still appeared pregnant (photo below). Such a long move so late in her pregnancy is quite unusual.
Finally, we also had a litter born in a holding bucket; a less than ideal situation but it provided an opportunity to collect some data not otherwise possible to get. Female 41’s transmitter was due for replacement early in July (transmitters function for about 12 months) but she had already gone into her gestation refuge and remained inaccessible ever since. I had resigned myself to her transmitter probably failing any day and having to search for her after she left her babies, along with Males 36 and 37 (who currently carry prematurely-failed transmitters). Then, last Monday, I was surprised to find her outside of her refuge, so I recaptured her. I don’t do transmitter surgeries during late-term pregnancy, plus it was apparent that she was likely to give birth very soon, so I planned to replace her transmitter as soon as she delivered her kids.
I didn’t have long to wait. She delivered nine healthy babies very early Friday morning (photo below). Her transmitter was replaced on Saturday and she, along with her brood, were released into her gestation refuge yesterday morning.
Here’s the interesting data that resulted from this captive birth: Subtracting mom’s body mass a few hours after birth from her body mass the day before revealed that she had lost 37% of her pre-parturition body weight. Average body mass of the kids was just under 14 g (about 1/2 ounce). Total body mass of her brood was 88% of her lost body mass, meaning that about 12% of her lost weight is attributed to amniotic membranes, fluid, etc. It is important to note that these live births are more akin to the egg-laying process than to mammalian births. That is, there is no placenta; the female rattlesnake secretes a yolk for each embryo that nourishes that embryo as it grows without further contribution from mom. Each embryo is contained in a thin transparent sac, rather than a thick egg shell (see the third photo in my Rattle Growth post from 14 July – click here). In addition to the embryo, the sac is filled with amniotic fluid and membranes enclosing what’s left of the yolk and the embryo’s waste.
The lesson from Female 41’s transmitter running out of time while she was not accessible is this: in the future, I will replace transmitters in females in May, regardless of the remaining battery life. For fifteen years, I have simply replaced transmitters at 12 months but Mohave Rattlesnakes in the desert were not reclusive during pregnancy and I just happened to have avoided summer anniversary dates for transmitters in females during my El Dorado Hills work.
So there it is… now you can amaze your friends with more than they ever wanted to know about rattlesnake reproduction!
Checking on our pregnant female rattlesnakes this morning disclosed another brood of kids in a different location. These appear younger than the ones discovered with Female 55 last night because their eyes are not yet cloudy white. Although only one was observed with the BurrowCam (see 19 second video), it is almost certain that there are more. Eight is the average litter size for Northern Pacific Rattlesnakes. However, these kids are also deep underground and, like those found last night, have only been observed with the BurrowCam.
Clearly, there will be baby rattlesnakes roaming around the American River Parkway within a few days, and some may have already shed and emerged from their mothers’ gestation shelters. Remember, the lack of snow pack and low reservoir levels have not affected the rodents and lizards along the American River, so the rattlesnakes are fat and healthy. Click here for more on how drought affects rattlesnake behavior.
Remember that, while venomous and dangerous, bites from baby rattlesnakes tend to be far less dangerous than bites by medium and large rattlesnakes. Clinical data comparing bites by rattlesnakes of different sizes clearly shows that big rattlers are more dangerous. Click here for a PDF of “Large snake size suggests increased snakebite severity in patients bitten by rattlesnakes in southern California” (2010, Wilderness and Environmental Medicine 21:120–126).
The idea that babies are more dangerous is likely the most common rattlesnake myth. Regardless of how much of their venom babies inject, adult rattlesnakes have a lot more venom, so are capable of much worse bites. Think about it: laboratories that produce venom to sell to pharmaceutical companies and other research institutions do not want baby snakes, they want big snakes because they produce a lot more venom. Data from these labs indicate that the venom yield from three-foot rattlesnakes is 100X the yield from one-foot juveniles. The photos below are actual venom extractions from a nearly three-foot male (left) and a 13-inch newborn (right) Mohave Rattlesnakes. I’d take a bite from the little one rather than the adult any day!
So there will be little rattlesnakes, about the size of pencils, around wooded and brushy areas for the next couple of months. To be sure, while their bites are less dangerous than bites by bigger snakes, any rattlesnake bite requires evaluation in a hospital emergency department without delay. By spring, the babies will be much more scarce because the little guys have many more predators than the adults.
This is just a quick post to announce the first births that we know of this year among our Effie Yeaw Nature Center rattlesnakes. When we checked on non-telemetered Female 55 this evening (Tuesday, 1 September) with the BurrowCam, she looked pretty normal (see photo below). She certainly did not look like she had lost a lot of weight. And there were no babies on or around her.
But when I bent the BurrowCam around and pushed it deeper into the cavity behind her, at least two babies were spotted. What was surprising was that they are not brand new. Note the bluish eyes and rattle caps; these kids are several days old – maybe close to a week.
These little guys have never been near the opening to the refuge when I have looked. That’s very different behavior than what I have seen in the past. Click here to see the 1.75 minute video of the kids.
Female 41 from the same shelter is still pregnant and there’s no evidence of kids around the other pregnant females…but I missed these babies for several days! More to follow soon…