Just a brief update to report that three or our six telemetered females (41, 39 and 53) have returned to the shelters where they have delivered broods in past years and all look quite heavy. Another, Female 66, is also stationary in a hollow log with a full abdomen but she did not reproduce last year and, since 2016 was our first year monitoring her, we don’t know where she has gestated in the past. Female 75, who did produce kids last year, is not heavy, still on the move, and looks like she will skip this year. Female 80 was on the hillside at the bluff but I have recently lost her radio signal. She was heavy and I could not palpate embryos when I replaced her transmitter in early June but she had lots of material in her GI tract which complicates the exam. Hopefully, her new transmitter has not failed…
Our females continue to often produce offspring during consecutive years, sometimes three years in a row before taking a year off. As mentioned before, this is not the norm for temperate-latitude pitvipers. While annual reproduction is common in the tropics where it never gets cold, the shorter warm season this far from the equator usually means that females need a year or two between broods to replace body fat before they can reproduce again. Conditions for our rattlesnakes are obviously quite good (even in past “drought” years), allowing them to replenish their weight quickly after losing 30%–50% of their body mass when they give birth.
Finally, I thought you’d find this photo interesting. Our big beautiful Male 37 was just in for his transmitter change two days ago and had obviously consumed a ground squirrel just before I captured him.
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.
Lots of you have been asking me how the rattlesnakes are doing with all the high water coming down the American River from Folsom and Nimbus Dams.
Well, the telemetered rattlesnakes are all in the oak forest and well above the high water. You may recall that Females 53 and 75 both gave birth to their broods a few months ago out in the flood plain near the usual river channel. And since December, both of their birth sites have been covered periodically by lots of fast-moving water.
The good news is that these females returned to higher ground shortly after their kids completed their neonatal sheds and dispersed from their birth sites in the fall and both have been tucked into their usual winter shelters since cold weather set in. We know that, of course, because of the radio transmitter each carries in her abdomen.
The fate of their babies, on the other hand, is not known. As I have mentioned before, we cannot effectively radio-track the little ones because we do not have tiny transmitters that will last long enough to make surgeries worthwhile. In other words, it is not practical to surgically replace transmitters every few weeks, which would be necessary due to the tiny batteries such transmitters use.
One thing we do know about baby rattlesnakes, however, is that few of them survive their first six months of life. They are frequently encountered in September and October, shortly after birth, but they’re scarce by spring. We know they have many predators when they’re small but it is also not hard to imagine the little ones born in the riverbed remaining there for the winter and perishing in the flood. If so, that is just natural selection in action: those rattlesnakes, adult or baby, that fail to seek higher ground for the winter are less likely to survive and pass their genes on to future generations.
Keep in mind that, on average, if a pair of rattlesnakes – or any other kind of animal – produces more than replacements (i.e., kids that reach maturity and reproduce) for themselves in their lives, we would be swimming in rattlesnakes! Put another way, on average over time in a stable population, animals are just replacing themselves… which means that most offspring never live to adulthood.
If you have been reading my blog for very long, you will have read this before: Nature is a cruel mother! Most wild animals’ lives end in the jaws of another…or sometimes in a flood. That’s just the way it is.
On a brighter note, we started seeing some basking rattlesnakes on sunny days by the end of February last year. So we may well be within a few weeks of the kickoff of the 2017 rattlesnake season! (Remember, watch where you put your hands and feet once the weather turns warm and leave rattlesnakes alone when you encounter them and your chance of being bitten is very near zero!)
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.
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.
Before I launch into what’s been going on with the Effie Yeaw rattlesnakes over the past few weeks, I want to pass on a link to a recent interview with Dr. Bree Putman. Bree was a grad student with Matt Holding (lead author of the journal article I linked to in my last post) in Emily Taylor’s lab at Cal Poly San Luis Obispo before she moved on to Rulon Clark’s lab at San Diego State to finish her Ph.D. In Bree’s interview (click here), she talks about ground squirrels and northern Pacific rattlesnakes and she describes some of the very intriguing behavioral questions many of us would love to answer.
Back to EYNC rattlesnakes –
I have not seen a courting pair of rattlesnakes since 28 April, when three rattlesnake pairs were found together in different locations. Male 37 was found with unmarked adults that were likely females on 11 and 14 May but no courtship was observed. But as the spring courtship season wound down, California ground squirrels began producing pups and the emphasis of both rattlesnake sexes turned to hunting.
After not finding a telemetered rattlesnake in or very near a ground squirrel burrow during the first 400+ observations this year, Male 46 was found in an ambush coil facing an active burrow a foot away on 9 May. In the five weeks since, several rattlesnakes have been found close to or inside squirrel burrows on several occasions.
At the same time, the snakes have also been hunting heavily in vole (aka: meadow mouse; Microtus californicus) tunnels in the grass.
And since about the end of May, the rattlesnakes – especially males – have been shedding.
Periodically shedding the corneal layer of the skin (called ecdysis; for more info, click here) takes snakes out of commission for a week or more and males seem to put it off during the spring mating season. It’s a bit like race car drivers waiting for a yellow caution flag to make a pit stop!
Even more interesting is that the rattlesnakes have favorite places where they go during this process and it is not uncommon to find several pre-shed individuals of both sexes together this time of year. Like hibernation, there seem to be many logs and burrows where they could shelter while waiting to shed but they congregate in just a few of them. Those of us who study rattlesnake behavior would love to know why. What is so special about certain locations? Or is it something else… like family ties or some other social interaction?
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.
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!
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…
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.