reproduction – EYNC Rattlesnake Study

Year end wrap-up

Well, it has been more than two months since I reported the first births of the year among the wild rattlesnakes in the Effie Yeaw Nature Center preserve. And while my hectic fall schedule prevented me from investing as much time as usual, I was able to record enough detail to compare this season’s behavior to previous years.

If the timing of the first births among our telemetered females (between 8 and 12 September) were representative of the larger population, we would expect to start encountering youngsters about the third week in September. Remember, new kids remain with their mothers in their birth shelters until their first shed, which usually occurs a little over a week after birth. Only then do they venture out into the world where people might encounter them.

Sure enough, the first young-of-the-year was encountered on 26 September, ironically on the sidewalk just outside the EYNC classroom as my UC California Naturalist class was leaving that evening. Of course, since I had just talked about baby rattlesnakes in class a few minutes before, the students were suspicious that I might have planted the little guy! The next day, I encountered another one (see photo below) stretched out next to the hollow log where Females 39 and 53 had recently given birth.

Young-of-the-year on 27 September, beside the hollow log where he was probably born.

Two shed “skins” (actually, just the outer or “corneal” layer) left by babies as they embark on their hazardous new life. Few survive to adulthood; at the size of pencils, they have lots of predators.

And sure enough, Female 39 once again made a beeline from her birth shelter to the blackberry thicket across San Lorenzo Way as soon as her kids’ natal sheds were complete (photo below). She has produced broods in three of the last four years and she has followed the same pattern each time: she used the same gestation/birth shelter, she made a direct 200+ meter move to hunt in the same blackberry thicket as soon as her kids departed, then she returned directly to her usual hibernation site after several weeks of foraging among the blackberries. Some of these individual rattlesnakes have proven to be quite predictable from one season to the next… but not all of them.

A slender postpartum Female 39, cryptically basking on the other side of San Lorenzo Way.

Female 41 spent the past three winters apparently by herself (as far as I could determine) in a ground squirrel burrow among the roots of a large living Valley Oak. However, she has apparently decided to spend this winter under the EYNC Visitor Center building! Now before getting excited, remember that she is one of only twelve rattlesnakes carrying radio transmitters at EYNC – and we have estimated that there are about 100 additional adult rattlesnakes in the preserve. We can make that assessment because we have 52 rattlesnakes marked with paint in the rattles that are not implanted with radios… and about half of our chance encounters with rattlesnakes without radios over the past year have been with unmarked animals.

Almost none of the EYNC staff or regular long-term visitors with whom I have spoken thought there were anywhere near that many rattlesnakes in the preserve. That’s a testament to just how secretive and non-aggressive rattlesnakes really are. It is highly likely that other rattlesnakes over-winter under the Visitor Center every year undetected.

It is simply prudent in rattlesnake country to be careful where you step and where you put your hands; simply look before you step or reach. Assume that a rattlesnake could be encountered anywhere – in any shed or under any wheelbarrow – and proceed with reasonable caution, not fear. Don’t walk around outside at night without a flashlight (or boots); while usually pretty timid, rattlesnakes really dislike being stepped on! That’s the same advice I have given countless people at my rattlesnake presentations.

As of 7 November, all but three of the telemetered rattlesnakes had returned to their previous hibernacula (hibernation shelters): exceptions are Female 41, who is under the Visitor Center 185 meters (a little over 600 feet) from her usual hibernaculum in the woods, Male 46 is on the hillside below the residential area instead of 265 m (about 870′) away under his usual log in the meadow, and Female 66 is under a new log 80 m (about 260′) from her usual log near the study pond.

The study comes to an end

As some of you know, 2017 will be my last year of data collection at Effie Yeaw Nature Center. We implanted the first transmitter in an EYNC rattlesnake in May 2014 and built up the group of telemetered rattlesnakes that summer. As a result, we have good data from three complete seasons during 2015, 2016 and 2017, plus many valuable observations from 2014. I will remove the transmitters from the remaining rattlesnakes in the spring and release them. Several are carrying their fourth transmitter (they must be replaced annually), so removal will be their fifth surgery. I also have blood samples in my refrigerator from nearly 70 wild EYNC rattlesnakes, as well as many dozens of shed skins collected from various locations in the preserve… and DNA can be extracted from both blood and shed skins.

Now the real work begins. Field work is great fun! Sitting at a computer for weeks or months is, of course, far less entertaining. Yet the field work means nothing if the data are not analyzed and shared. And as a favorite mentor of mine is fond of reminding me, “If you don’t publish it, it never happened!” So, while we certainly have answers to the original questions (like how many rattlesnakes are there, where do they give birth, spend the winter, etc.), the most exciting part involves the potential for unexpected discoveries. And as I have written about in this blog before, I have found the EYNC rattlesnakes associating in three loose groups without an obvious environmental reason to do so. I suspect they are socializing in family groups, which has only been documented in one previous case with Timber Rattlesnakes (Crotalus horridus) in the Appalachian Mountains. Genetic analysis of the blood and shed skins will make or break that hypothesis for the EYNC animals. I will continue to post analysis updates and eventually publications here.

So stay tuned!

I’ll leave you with one of my very favorite photos from the study: big Male 37 basking peacefully on top of a large pile of dead branches among blackberry and wild grape vines early one morning in April 2016. The third rattlesnake to receive a transmitter at EYNC, he has always been a joy to watch and has provided some of my most memorable rattlesnake encounters of the last four years. The yellow and red paint in his rattle is slightly visible in the photo. Like others of his kind, he wants nothing to do with people but is a mouse, vole or ground squirrel’s worst nightmare.

Gestation has begun for pregnant females

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…

Female 41 in the same hollow log where she gestated and delivered broods in 2014 and 2015. She took last year off and hunted throughout the summer. These images are made with our BurrowCam (actually an inspection camera made by Rigid Tools).

Radio signals from Females 39 and 53 are currently coming from this hollow log. Female 39 produced broods here in 2014 and 2015. She hung around here last year but we are not sure she produced kids; she was never very large and we never spotted babies but she behaved like she reproduced. We’re just not sure. Female 53 produced offspring here in 2015 and gestated here for a while in 2016 before moving to a shelter in the dry riverbed to give birth. Since we cannot see the rattles on these two, it is impossible to tell if these are Females 39 and 53, since other pregnant females often share this shelter. Photo with the Rigid BurrowCam.

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.

Male 37 anesthetized for surgery yesterday morning. I was surprised at how much of his meal he digested overnight… the squirrel was better defined and the bulge was even larger just a day before. This was probably a half-grown ground squirrel pup. These pups are everywhere right now, are easier for the rattlesnakes to kill, and an adult squirrel would have made a really enormous bulge in the snake. Just for reference, the rule is a “meter stick” and the snake is about 40 inches long. The small bump on his left side behind the squirrel is a bit of shed skin (actually just the corneal layer of the skin) stuck in the scar from his last transmitter surgery. Shortly after this photo, he received his fourth transmitter and was released yesterday back into the EYNC preserve.

Will rattlesnakes be more abundant this year?

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.

How are the rattlesnakes doing in the flood?

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.

Water level on 17 January, looking out at the spot where Female 53 delivered her young a few months ago. Water flow on this day was reported to be 30,000 cubic feet per second (cfs). Days earlier, it had been much deeper when flowing at 60,000 cfs!

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!)

More baby news

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.

Recovered neonatal exuvium from ground squirrel burrow occupied for weeks by Female 75; 23 September 2016 Original DROID IMG_20160923_125147783.jpg — Recovered neonatal exuvium (shed corneal skin layer) from the ground squirrel burrow occupied for weeks by Female 75. Tying a tool designed to retrieve dropped screws to the Burrow Camera allowed the “skin” to be fished out of the burrow.

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)

Postpartum Female 53. Note the long lateral fold of empty skin along her abdomen, typical after loosing 30-50% of her body mass during birth. — Postpartum Female 53. The long lateral fold of empty skin (yellow arrows) along her abdomen is typical after loosing 30-50% of her body mass during birth.

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.

First baby rattlesnakes of the season at EYNC

We have kids!

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.

Females 39 (red/blue) and 53 (blue/yellow) laying together in their gestation shelter on Saturday, 3 September, illuminated by sunluight reflected from a mirror. Both were still pregnant. They are laying on top of a recently shed skin from another large rattlesnake. — Females 39 (red/blue) and 53 (blue/yellow) laying together in their gestation shelter on Saturday, 3 September, illuminated by sunlight reflected from a mirror. Both were still pregnant. They are laying on top of a recently shed skin from another large rattlesnake.

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.

A newborn northern Pacific rattlesnake in the hollow log with females 39 and 53 on 6 September. His eyes are still clear, indicating he is no more than a day or two 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.

Female 66 is almost hidden by an unmarked male courting her on 29 August 2016 — Female 66 is almost hidden by an unmarked male on top of her on 29 August 2016. Note his tail wrapped around and under hers.

Female 66 copulating with an unmarked male on 29 August 2016 — The same pair copulating two hours after the photo above was made. The marked and telemetered female has white paint in the top half of her rattle; the male’s rattle is not marked with paint.

Emphasis now on hunting and shedding

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 –

This female California ground squirrel was clearly nursing pups on 26 April at Effie Yeaw Nature Center. — This female California ground squirrel was clearly nursing pups on 26 April in the Effie Yeaw Nature Center preserve.

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.

Male 46 visible in a vole tunnel on the morning of 3 June 2016. Original RAW IMG_2192.CR2 — Male 46 uncovered (arrow) in a vole tunnel in the grass on the morning of 3 June. Although you cannot see it here, voles construct a maze of above-ground tunnels in thick dry grass that protects them from most predators… but not rattlesnakes. I hope you can appreciate just how impossible it would be to learn about the habits of these snakes without radiotelemetry!

And since about the end of May, the rattlesnakes – especially males – have been shedding.

Pre-shed Male 38 on 14 June 2016 Original RAW IMG_2320.CR2 — The rattle of pre-shed Male 38 under a log yesterday, 14 June. The new rattle segment forming in the base of the tail is whitish and covered by the last couple rows of scales. He is easily identified visually by red/green paint in his rattle.

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?

Courtship has begun

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).

Female 55 basking alone in the afternoon sun on 22 March 2016. Note her rattle with red over yellow paint, visible through the grass on the left side of the photo. Without a radio, she had not been seen since June of last year.

type here — Then two days later, on 24 March, Female 55 is almost completely hidden by a new male on top of her; you can see his unmarked rattle in the middle foreground of the photo. Although the male is distracted by me in this picture, he had been vigorously courting the female just moments before. Unfortunately, the video camera auto-focused on the grass, making the resulting image unusable. Courtship continued at this location for at least three days but they were gone on 29 March, replaced by Male 35, who was enjoying the sun by himself yesterday afternoon. Although he would retreat under the log when I approached closely, he would re-emerge within minutes as soon as I backed away.

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.

More baby rattlesnake info

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.

Six-day-old babies basking at their El Dorado Hills birth site in September 2011. Mom is out of sight just behind them.

Female 47 with a couple of her 2014 brood on 15 September. Original RAW IMG_2670.CR2 — Female 47 with a couple of her 2014 brood at Effie Yeaw Nature Center on 15 September last year.

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.

OK, you have to say, "Awww. aren't they cute!" even if you're not fond of rattlesnakes. This is Female 41 reunited with her kids after her transmitter surgery on Saturday. They were released together the next day and should remain together for another 10 days or so.. — OK, you have to say, “Awww, aren’t they cute!” even if you’re not fond of rattlesnakes. This is Female 41 reunited with her kids after her transmitter surgery on Saturday. They were released together the next day and should remain together for another 10 days or so.

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!

Baby rattlesnakes!

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.

Frame grab from BurrowCam video of Female 55, not looking like she's lost much weight. No kids in sight just inside her refuge Tuesday evening - or anytime previously. — Frame grab from BurrowCam video of Female 55, not looking like she’s lost much weight. No kids in sight just inside her refuge Tuesday evening – or anytime previously.

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.

One of at least two babies in the refuge with Female 55 on Tuesday evening. Note the bluish eyes and rattle button. These little snakes are several days old and already preparing for their postpartum shed.

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…