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.

 

Baby season update

Just a quick update on our reproductive females:

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.

Fresh neonatal shed "skin" (actually, the shed outer or "corneal" layer of the skin) in the log where Female 39 has been gestating since 14 June.
One of the neonatal shed “skins” (actually, just the outer or “corneal” layer of the skin) found this morning in the log where Female 39 has been gestating since 14 June.

 

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:

Female CROR 53 in streambed burrow Frame grab at 47 seconds into original BurrowCam video; 15 September 2016
The place to look for the shiny moving baby in the video is circled in this still frame grab.

Also, compare the appearance of her abdomen in today’s video to her 3 September photo (in my last post).

Female CROR 53 in streambed burrow Frame grab at 57 seconds into original BurrowCam video; 15 September 2016
Female CROR 53 in her streambed burrow at 52 seconds into the video clip. The violet sutures remaining from her May transmitter surgery are circled, indicating that we are looking at her posterior abdomen, which is no longer swollen.

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.

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.
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.

Pregnancy, growth and drought

We currently have transmitters implanted in six female rattlesnakes. We have been tracking Female 39 since 2014 and Females 41 and 53 since 2015 and all are currently pregnant and in their gestation shelters where they will likely thermoregulate for six weeks or more. Furthermore, they have all produced a brood during each season we have been following them, so this will be the third year in a row for Female 39 and the second in a row for 41 and 53. And we don’t know how many consecutive years they might have reproduced before that! Each has returned to the same gestation refuge each year, although 41 uses a different location than 39 and 53, who gestate together. We have also found pregnant unmarked females in both places in past seasons with these girls.

That’s not all. We have three new females this season, numbers 66, 75 and 80. These snakes do not appear to have settled into gestation shelters yet (and I don’t know where they were in previous years) but I just implanted a transmitter in Female 80 a few weeks ago and could feel six fetuses in her belly…it felt like she had swallowed six soft ping pong balls! I’m not sure about the reproductive status of 66 and 75, since their surgeries were earlier in the year and both had so much material in their intestines that it made identifying small embryos with confidence difficult.

Another opportunity to assess the health and growth of the rattlesnakes at Effie Yeaw Nature Center occurred day-before-yesterday (13 July) when Kelly came across an adult rattlesnake at the end of the Visitor Center building early in the morning. Per protocol, she expertly maneuvered it into the capture bag and deposited it in the holding barrel for me. It turned out to be Male 52, a rattlesnake previously captured, processed, and released without a transmitter early in May 2015. At that time, he was 30.7 inches in total length and weighed 11.6 ounces. He now measures 33.5 inches and weighs 18.9 ounces. While increasing 9% in length and 63% in mass in 14 months, he has shed three times (see photo below).

For those of you new to the blog, I inject acrylic paint into the first hollow segment of the rattle
For those of you new to the blog, I inject acrylic paint into the first hollow segment of the rattle, next to the black live segment at the end of the tail. With a different color combination for each snake, it allows me to visually identify them. As the snake grows and sheds the corneal layer of its skin periodically, it produces a new rattle segment with each shed. The segment with the paint is thus moved away from the tail until it eventually breaks off. When this seems imminent, as in Male 52 above, I inject paint into another segment to preserve the marking.

 

The constant growth of all the rattlesnakes being sampled and the annual reproduction of many of the females attests to the health of not just the rattlesnake population but the overall small animal community in the riparian habitat at Effie Yeaw Nature Center. While the region is undeniably in a severe long-term drought, enough local rainfall has occurred to keep the annual plants, shrubs, some trees, and the food web they support healthy.

Finally, I want to share with you a little bit about a presentation I made at the annual Joint Meeting of Ichthyologists and Herpetologists last week in New Orleans. I have reproduced the published abstract (summary) of my talk below. Please excuse the Latin names. Crotalus scutulatus is the scientific term for the Mohave rattlesnake and Crotalus oreganus is our own northern Pacific rattlesnake. While recent drought has not yet affected the rattlesnakes or their prey in the areas of northern California I have sampled, 2002 was a rainless year in the Mohave Desert, with no plant growth and a dramatic reduction in the availability of kangaroo rats and other small mammals that make up the great majority of the rattlesnakes’ diet there. During 2002, Mohave rattlesnakes changed their behavior very significantly, staying tightly coiled and avoiding wind and sun while moving very little and not courting or mating.

Cardwell abstract

The take-home message I delivered in New Orleans was that (1) these animals are used to hot dry summers and get most of their water from their prey; (2) regional drought does not necessarily equal local drought; (3) rattlesnake behavior is probably not affected by drought until prey availability is affected; (4) water-stressed rattlesnakes minimize exposed skin by remaining coiled most of the time; (5) when water-stressed, they don’t move more, they move a lot less than usual; and (6) there is no evidence that they leave their normal home range during a drought.

In other words, there is zero evidence to support the frequent news media claims that drought drives rattlesnakes into yards.

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?

 

Male 36 finally recaptured!

If you have been following my rattlesnake study from the beginning, you know that we struggled through some faulty transmitters early in the project (search “failed transmitters” for previous info). The first six transmitters I implanted failed early. Several failed during hibernation (2014/15) and, because I knew where the snakes spent the winter, I was able to capture them when they began basking in the spring. Two, however, proved to be a bigger problem.

Male 36’s transmitter was first to fail in September 2014, with two months of activity remaining that season. Male 37’s transmitter lasted into the winter but he hibernated high on the bluff under a thick mat of vegetation, making his exact location very difficult to visit and impossible to pinpoint. Thus, both emerged in the spring of 2015 without functioning transmitters.

Both eluded recapture until October 2015, when I found Male 37 (details here) under the log I call “The Community Center” because everybody visits it from time to time. Males visit looking for girls, pregnant females hang out there to thermoregulate and give birth, and both sexes use it for shelter while waiting to shed (but nobody spends the winter there). I replaced Male 37’s transmitter then, leaving only Male 36 unaccounted for – until last week.

After twenty months, I had just about given up on finding Male 36 again. But when I checked around The Community Center one day last week, I was thrilled to spot his rattle with red/red paint! Like Male 37 last fall, Male 36 was also pre-shed and using The Community Center for shelter while he waited to complete the process.

Pre-shed Male 36, with failed transmitter, at Refuge 01, Effie Yeaw Nature Center, on 11 May 2016, moments before his recapture. Original RAW IMG_1531.CR2
Pre-shed Male 36, with failed transmitter, at The Community Center on 11 May 2016, moments before his recapture. If you look closely (partly obscured by grass), you can make out the new light-colored rattle segment forming under the skin at the rattle base.

 

Just like Male 37, I captured Male 36 and kept him several days until he shed. His transmitter was replaced and he was released yesterday.

Male 36 disappearing into
Male 36 disappearing into The Community Center yesterday with a new transmitter and re-marked rattle (his rattle is quite long and likely to break soon, potentially taking his original paint with it). Note how clean and crisp his pattern appears after shedding, compared to the photo above.

 

The return of Male 36 fills my permit quota of seven telemetered males. We currently have five females telemetered and I am holding out, hoping to get a couple of females radio-tagged farther out in the northeastern portion of the preserve where few of our current snakes venture. Interestingly, Male 38 was hanging around with two females out there last week, including last Saturday when I was hosting a video crew from UC Santa Cruz. While I would have loved to get a transmitter into one of them, they were too wary and repeatedly escaped when approached.

I wish more people could see just how hard these fascinating creatures try to avoid confrontations with people!

 

 

A death mystery and rattlesnake season winding down

Male 37

Our wayward male shed on the morning of 7 October, five days after being recaptured. His faulty transmitter was surgically replaced that afternoon and he was released the following morning.

CROR37 recovering from anesthesia on 07 October 2015. Original Droid IMG_20151007_162411334.jpg
Male 37 recovering from anesthesia on a heated pad after his transmitter surgery on 7 October. He now measures 969 mm (just over 38″) total length, making him the largest rattlesnake I have measured at Effie Yeaw. Besides shedding four times in the past 16 months, his body mass has increased 26% (now 668 g or 1.5 lbs.), while his length increased by almost 5%. This is a very healthy rattlesnake!
CROR38 at release on 08 October 2015 Original RAW IMG_9094.CR2
Male 37 on the morning of 8 October, disappearing into the hollow log where he was captured. Note that I marked his rattle again, since his original paint is only two segments away from being lost.

 

I took advantage of the necessity to allow Male 37 to shed before his surgery to collect some useful data. His pre-shed body mass was 693.5 g. By weighing him again and subtracting his post-shed mass of 668.4 g, we find that he lost 25.1 g (0.9 oz.), which was 3.6% of his body mass. Then, by drying his shed “skin” on a hot plate to drive off ambient moisture and subtracting that mass (5.1 g) from 25.1g, we can calculate that 80% of the mass he lost was water. Although these rattlesnakes are unaffected by California’s drought so far (more details here and here), that will eventually change and such data will be invaluable for calculating water loss and gain over time (water “flux”) and predicting when the snakes will become water stressed.

More Mortality

Another healthy postpartum female, CROR 47, was killed on the morning of 21 September. I may have been premature in assuming that a coyote killed Female 54 on 14 September (details). Female 47 was also very fresh when I found her, killed in the early morning in the meadow by something that did not eat her.

Death scene: CROR47 in meadow of Effie Yeaw Nature Preserve, morning of 21 September 2015 Original RAW IMG_8736.CR2
Death scene: Female 47 in the meadow at Effie Yeaw Nature Preserve on the morning of 21 September. The posterior end of her abdomen was laying a few feet away. The edge of the bright red transmitter can be seen in the grass near the middle of the photo. Clearly, the carnivorous yellow jacket wasps found her quickly.

It was obvious that Female 47 had been pulled apart, with her body in two large pieces and internal organs and strips of skin pulled away. But she was all there. Maybe most interesting was the condition of her head: The top of her head was intact and unmarked but her lower jaw was mostly gone and the roof of her mouth was mangled, especially where the fangs had been (caution: graphic close-up).

In reconsidering the death of Female 54 a week before, I assumed that her missing head and neck had been eaten but it is entirely possible that I just didn’t find them. And I rationalized that a coyote dropped the snake as it probably fled (unseen) from me. But I see coyotes around the meadow frequently and, while they give people a wide birth, they are not panicked by our presence. If I interrupted a coyote with Female 54, why wouldn’t it have carried the rattlesnake away to finish the meal?

So what would encounter both rattlesnakes in the meadow early in the morning and pull them apart before leaving them uneaten? I have had coyotes kill Mohave rattlesnakes in southern California in the past but they eat the entire snake and chew the transmitters; these transmitters were undamaged. And what would remove the jaw and mangle the inside of the mouth?

My best idea is turkeys. Interestingly, I have found nothing in the scientific literature about wild turkeys killing adult rattlesnakes, although there are several anecdotal accounts in books, including Laurence Klauber’s Rattlesnakes (1972, Univ. California Press) of turkeys mobbing adult rattlers. Inquiries of my rattlesnake researcher colleagues has produced one witnessed account of a wild turkey killing and eating a two-foot timber rattlesnake (Crotalus horridus) in Minnesota. And there is a video on YouTube of two turkeys apparently killing what appears to be a large gopher snake (Pituophis) on a golf course.

If anyone reading this has first-hand information about wild turkeys interacting with rattlesnakes, I would love to hear about it.

2015 Season almost over?

Well, it’s the last week in October and our eight telemetered rattlesnakes appear to be mostly settled into their winter shelters, despite relatively warm weather. Last year, we still had three telemetered rattlesnakes roaming around well into November (see my “Rattlesnake Update” from 26 November 2014).

This year, one of our telemetered animals has been stationary since 16 September and others have stopped moving since 6 October, 12 October (2 animals), and potentially three more in just the past couple of days. Most interesting of all is that five of them are in the same shelters they used last year – and a sixth may be on his way. This is a departure from behavior observed during my field work in El Dorado County, where the rattlesnakes did not return to the same locations winter-after-winter, although some returned to previously used sites after spending a winter or two in other locations.

This year at Effie Yeaw, our skinny geriatric Male 40 went immobile on 16 September under the same log he shared with Males 35 and 38 and Female 39 last winter. Then Male 35 and Female 39 joined him, arriving on 6 October and 12 October, respectively – although their radio signals indicate that they are not together under the large log. Male 38 is still on the move, even visiting the residents along Edgehill Lane three days ago (26 October). I was unable to gain access to his location due to the necessary residents apparently being away and, when I returned yesterday, I found that he had returned to the hillside within the nature preserve. Male 37 spent a few days in the same area on Edgehill Lane in August 2014 and also returned to the preserve before I could gain access to him. These are the only two times (in two full seasons) that telemetered animals have entered the residential area on the bluff. When this occurs, I try to contact the property owners and would remove the snake, if that’s the property owner’s desire and the snake is accessible. In both cases, however, the rattlesnakes  returned to the preserve before I could make contact with the necessary residents. But back to Male 38, he was on the hillside yesterday morning and may be headed back to last year’s log with the others.

Male 37 went directly to the hillside after I released him with a new transmitter on 8 October and I have not detected a change in the location of his radio signal since 12 October – which sounds like the same place he spent last winter (again, refer to my “Rattlesnake Update” from 26 November 2014). Once I’m sure he’s down for the winter, I’ll make the treacherous climb and verify his exact location.

Female 41 arrived on 20 October at the log where she spent last winter. She moved a few meters away over a couple of days but has been back for the past three days, so she may also be done for this season. As far as I could determine last winter, she was alone. Male 46 and Female 53, neither of which were telemetered last winter (i.e., I don’t know where they spent last winter), are very close together under another large log and have been there for at least three days.

It is interesting to note that the rattlesnakes that are already in their winter shelters are not basking, preferring to remain out of sight with body temperatures mostly in the 60–65F range. Earlier in the activity season, when cool nights are followed by warm morning sun, the rattlesnakes come out and warm up by exposing some or all of their skin area, depending on ambient temperature and the intensity of the solar radiation. But in ectotherms (animals that get their body heat from the environment) like rattlesnakes, body temperature varies with the environment and both metabolic rate and water flux increase with higher body temperature, burning more stored energy and using more water. So, on the verge of four or five months of hibernation, the rattlesnakes are likely programmed by evolution to cool off and slow their metabolism, thereby conserving energy and water for use in the spring.

Once I’m sure the snakes are done moving for the year, I’ll summarize the season’s findings in the context of last year’s data and our original questions and study goals.

 

Life and death among the rattlesnakes

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.

A post-shed young-of-the-year crawling over an unidentified adult inside RFG01EY on 10 September 2015. Original RAW IMG_8590.CR2.
A post-shed youngster crawling over an unidentified adult rattlesnake in its birth shelter on 10 September 2015.

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!

Recently postpartum female Northern Pacific Rattlesnake (CROR39) with recent food bolus, basking on 10 September 2015 near Effie Yeaw Nature Center. Original RAW IMG_8606.CR2.
Recently postpartum female Female 39 with recent food bolus, basking on 10 September 2015.

 

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.

Female CROR54 partly eaten, morning of 14 September 2015. Blood is not coagulated and exposed tissue is moist and glistening. Original Droid IMG_20150914_094119031.jpg
Female 54, partly eaten on the morning of 14 September. I suspect a coyote was having her for breakfast when I approached and interrupted his meal.

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.

Two-week-old youngster just emerged from his birth refuge, 1 m behind him. Original IMG_20150914_164416116.jpg
A two-week-old rattlesnake, less than a foot long, that had just emerged from his birth refuge. He (or she) was contemplating the big unknown and dangerous world for the first time.

 

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.

A kingsnake visits a birthing refuge occupied by two pregnant rattlesnakes
Captured by a time-lapse camera, this kingsnake was checking out a gestation refuge occupied by two pregnant rattlesnakes in September 2011, during my El Dorado Hills study. Both females gave birth within the following week. Baby rattlesnakes are just hors d’oeuvres for kingsnakes, which probably know very well where the rattlesnakes give birth and they may well eat a large percentage of newborn rattlesnakes.

 

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!

 

Missing males and waiting for kids

As birthing season approaches, I have been watching intently for signs of baby rattlesnakes. While postpartum mothers usually stay inside their shelters, the neonates are typically active and easily spotted. Although they do not leave their shelters before shedding the first time, babies can usually be seen crawling or basking at the entrance. And when we introduce the BurrowCam into the shelter, the kids can be seen exploring their new surroundings and crawling around on their mother. So far, there’s been no evidence of babies yet this year. This would be a bit early but quick warming last spring has me wondering about the potential for early births this year.

Remember that pregnant female rattlesnakes in our area hangout in carefully selected thermal shelters where they can maintain consistently warm body temperatures around the clock until they give birth. This period of thermoregulation lasts several months, during which the pregnant moms do not forage for food.

All five of our telemetered females are apparently pregnant, plus Female 55, who was processed and released without a transmitter in June (no transmitter surgery due to some old but significant trauma to her abdomen; click here for details). These females settled into their gestation shelters between 8 June and 1 July and have maintained body temperatures between 28ºC and 32ºC (82º–90ºF), almost without exception, ever since.

In fact, at dawn on a recent cool morning (16 August) when the ground temperature just before sunrise was in the mid-50s F, these girls still had body temps in the high 80s F. They maintain similar body temps during hot afternoons when the ground temperature (much hotter in the sun than air temp) outside is 120ºF and more. They thermoregulate like this by selecting logs or large rocks that have just the right thickness and sun exposure to stay warm at night but not get too hot in the afternoon sun. Such places are apparently scarce because three of our telemetered females are together in one shelter, while Female 41 is with non-telemetered Female 55 in another. Female 54 is in a third location, possibly by herself, but there could be others in there without radios. Females 39 and 41, both of whom produced broods in 2014, are in the same shelters as last year.

Flash photo of Female 41, tucked into her gestation refuge at sunrise on 16 August 2015. Note in the inset how her scales are pulled apart by her developing brood. Female 55 is also in this shelter but not visible on this morning.
Flash photo of Female 41, tucked into her gestation refuge at sunrise on 16 August 2015. Note in the inset how her scales are pulled apart by her developing brood. Female 55 is also in this shelter but not visible on this morning.

On 27 August, the BurrowCam revealed Female 39’s abdomen to be greatly distended, extending all the way to the cloaca. So maybe delivery of her 2015 brood is not far off? The frame grab (below) from the BurrowCam video shows her abdominal scales pulled far apart. In the 50-second video (watch here), you’ll see what I see when we thread the BurrowCam into a passage. Female 39 is identified by red/blue (red-over-blue) paint in her rattle and the edge of another dark gray rattlesnake appears to be visible under 39’s coils. Known to be behind her in the passage (because of their radio signals) are Females 47 and 53, as well as Male 46. Additionally, in recent days, I have seen non-telemetered (and non-pregnant) Female 48 (green/green) and Male 36 (red/red; carrying a failed transmitter) in this log. It’s a popular place this time of year!

Frame grab from a 27 August BurrowCam video of the distended abdomen of telemetered Female 39, deep in her gestation refuge.
Frame grab from a 27 August BurrowCam video showing the distended abdomen of telemetered Female 39, deep in her gestation refuge.

As you may recall, Males 36 and 37 have been missing for months since their transmitters failed prematurely in September and December, respectively. Until last week, Male 36 had been last seen on the BurrowCam in a hollow log courting postpartum Female 41 on 2 October 2014, and I last saw Male 37 as his tail disappeared down a hole on 7 March 2015. There had been no sign of either of them since until a fellow photographer and herpetologist I encounter frequently at Effie Yeaw showed me a photo of Male 37 (IDed by his yellow/red rattle marking) crossing a trail on 20 August! Then, just 5 days later, while checking for babies in the shelter with Females 39, 47 and 54, and Male 46, I was surprised to see Male 36’s red/red rattle. (See photos below) So both are alive and well… but both still elude recapture.

Male36 (red/red paint in rattle) deep inside a hollow log with Female 41 on 02 October 2014.
Male36 (red/red paint in rattle) deep inside a hollow log with Female 41 on 02 October 2014.

 

Male 36 inside another hollow log on 25 August 2015 with at least three pregnant females and a smaller male. Compared to the 2 October photo (above), note that he has two additional rattle segments between the paint and the live black segment, indicating he has shed twice in the past ten months.
Male 36 inside another hollow log on 25 August 2015 with at least three pregnant females and a smaller male. Compared to the 2 October photo (above), note that he has two additional rattle segments between the paint and the live black segment, indicating he has shed twice in the past ten months.

Earlier today, 29 August, I found Male 46 coiled in poison oak dozens of meters away from the log where he has been hanging out with the three pregnant girls continuously for the past two weeks. It is likely he has been chased off by a larger male, so maybe Male 36 is still in there. This refuge has a narrow deep passage that is nearly impossible to thread the BurrowCam into and, even when successful, I can usually only see whichever rattlesnake is closest to the top (for example, the 50-second video of Female 39, with the link earlier in this post).

So Baby Watch continues and I still hope to recapture missing Males 36 and 37.

Rattle Growth, Shedding & Estimating Age

Now is the perfect time for this discussion because the Effie Yeaw rattlesnakes have been shedding like crazy. Since the end of spring courtship about two months ago, the pregnant females have hunkered down to thermoregulate at optimum gestation temperature while the males and non-reproductive females have been hunting with far less attention to temperature control. All have been shedding over the past few weeks.

If you haven’t yet read my description of the shedding process near the end of my last post, do so now; the following discussion will make much more sense with that background.

Because the corneal layer of the skin does not grow, shedding (or ecdysis) is a recurring process throughout a scaled reptile’s life. Like other animals, baby snakes grow rapidly, so they must replace the corneal layer frequently to accommodate rapidly expanding bodies. Since shedding frequency is highly correlated with growth rate, juveniles usually shed several times per year. Growth rate and shedding frequency slows with size and age, with large adult rattlesnakes sometimes shedding less than once per year.

Rattle growth is a fundamental part of the shedding process for rattlesnakes. The rattle is made of keratin, the same stuff as the acellular matrix of the corneal skin layer – and your fingernails. Each time the snake generates a new corneal layer and prepares to shed the old one, it also produces a new rattle segment. Thus the newest segment is always at the base of the tail and contains live tissue – much like the base of your fingernail. And because each new segment is the width of the tail, young rapidly-growing rattlesnakes produce a tapered rattle (photo below).

Male northern Pacific rattlesnake, Crotalus oreganus (CROR46), 09 March 2015 Original RAW IMG_5583.CR2
Our Male 46 on 09 March 2015, just before his rattle was marked with paint. All segments except the newest are hollow and dry.

The rattle is made up of loose, hollow, interlocking segments. Except for the first segment (or “birth button”), each segment consists of three lobes, yet only one is visible. The two hidden lobes fit loosely inside the older adjacent segments (photo, below). There is nothing loose inside that makes noise, the rattlesnake’s buzz comes from the loose segments vibrating together.

A single rattle segment from a mature rattlesnake, showing the three-lobed structure (left). On the right is a back-lit rattle from an old rattlesnake (note the lack of taper) showing how the segments interconnect. Older segments are at the top of the photo.
A single rattle segment from a mature rattlesnake, showing the three-lobed structure (left). On the right is a back-lit rattle from an old rattlesnake (note the lack of taper) showing how the segments interconnect. Older segments are at the top of the photo.

 

Rattlesnakes are born with a tiny hard cap on the end of the tail. I like to use the analogy of an eraser on a pencil – which is the approximate size of the newborn snake and the cap.  During the first ten days or so, the first rattle segment or “birth button” is produced, which is uncovered by the postpartum shed. This is the only time that a part of the rattle comes off with the shed “skin.”

Rattle cap of a neonatal Southern Pacific Rattlesnake (Crotalus oreganus helleri), about a minute old and still in its amniotic sac.
Rattle cap of a neonatal Southern Pacific Rattlesnake (Crotalus oreganus helleri), about a minute old and still in its amniotic sac.
Rattle of a one-week-old Southwestern Speckled Rattlesnake (Crotalus mitchelli pyrrhus) showing the newly-formed birth button inside the rattle cap, which will be lost with the post-partum shed in a few days.
Rattle of a one-week-old Southwestern Speckled Rattlesnake (Crotalus mitchelli pyrrhus) showing the newly-formed birth button inside the rattle cap, which will be lost with the postpartum shed in a few days.
"Skins" from post-partum sheds showing the neonatal rattle caps. The one on the right is in its natural condition (inside-out); the one on the left has been manually everted to expose the cap.
“Skins” from postpartum sheds showing the neonatal rattle caps. The one on the right is in its natural condition (inside-out, with the cap hidden inside); the one on the left has been manually everted to expose the cap.
Birth button of two-week-old Northern Pacific Rattlesnake after post-partum shed. This is the first rattle segment and will stay with this animal until it gets too dry and brittle, which will allow it to break off while being dragged through the brush in a few years.
Birth button of a two-week-old Northern Pacific Rattlesnake after its postpartum shed. This is the first rattle segment and will stay with this animal until it gets dry and brittle, which will allow it to break off while being dragged through the brush in a few years.

During every subsequent shed, the old corneal layer will simply be an open tube that slips over the rattle. When a shedding cycle begins, formation of the new rattle segment is usually noticeable before the eyes turn blue (photo, below).

On 24 June, the tail of Female 54 showed early tell-tale evidence of a shedding cycle beginning. The black segment is the live one but notice how the scales next to it look almost transparent and the tissue beneath is much lighter... that is a new segment beginning to form.
On 24 June, the tail of Female 54 showed early tell-tale evidence of a shedding cycle beginning. The black segment is the live one but notice how the scales next to it look almost transparent and the tissue beneath is much lighter… that is a new segment beginning to form.
A week or so further along in the shedding cycle than Female 54 (above), the tail and rattle of Male 46 last May illustrate the progression of growth of a new segment in the end of the tail. During the process,  live tissue receeds from the last new segment (next to the paint),  leaving it hollow and dry after the old corneal layer is shed.
A week or so further along in the shedding cycle than Female 54 (above), the tail and rattle of Male 46 last May illustrate the progression of growth of a new segment in the end of the tail. During the process, live tissue recedes from the last new segment (next to the paint), leaving it hollow and dry after the old corneal layer is shed.

Injecting acrylic paint into the first hollow segment allows me to identify rattlesnakes visually, with each animal receiving a unique color combination. The paint also allows me to record how often they shed.

This is the rattle of my Female 05 from El Dorado Hills in October 2013. The paint in the middle of the rattle is from her initial capture in June 2010. I marked her rattle with new paint in 2013 (next to the black live segment) because the older segments will eventually dry, crack, and break away, taking the original paint with them.
This is the rattle of my Female 05 from El Dorado Hills in October 2013. The paint in the middle of the rattle is from her initial capture in June 2010. I marked her rattle with new paint in 2013 (next to the black live segment) because the older segments will eventually dry, crack, and break away, taking the original paint with them.

In Female 05 (above), note that her birth button and the next two or three segments are already missing. The location of her original paint tells us that she has shed four times in the 40 months since she was first marked. The slight taper at the end of her rattle provides a hint of her age: considering the number of segments I think are missing and that snakes grow much faster and shed more frequently when young, I estimate that I originally captured her in her third or fourth year, making her about seven years old in this photo. Once all of the tapered segments at the end are lost, we have no way of estimating how old she is from the rattle.

You can also see that the rattle segments produced by Fem 05 (photo, above) as a young rattlesnake are noticeably larger than the more recent thin segments. This happens in the middle of rattles, too, with some segments being wide and robust while others are thin. I think rattle segments are a bit like tree rings in that good conditions with lots of  food produce wider thicker segments. In the case of adult females like 05 above, it likely reflects the shift in resource allocation (more below) when she became sexually mature. It is worth mentioning that this snake had reproduced three years in a row when this photo was made (and she produced the four recent thin rattle segments) and her body condition was very poor after three consecutive litters.

In almost all rattlesnake species, adult males are larger than adult females. Yet the growth rate of baby males and females is indistinguishable until they reach sexual maturity. Once they start reproducing, however, female growth slows. We believe this happens because females start diverting most nutritional resources to the production of offspring, leaving much less available for their own growth. Males, on the other hand, are free to continue devoting their resources to increased body size – which is advantageous for fending off predators while searching for females and for battling other males for access to receptive females (click here for video of males fighting).

Finally, can we tell a snake’s age from the rattle? The one sure thing is that each rattle segment does not represent one year. The addition of rattle segments is well correlated with growth rate which, in turn, depends on age and food intake. We can make a pretty good estimate of age from a complete unbroken rattle and even when a few segments are missing, so long as some significant taper remains at the end. But for older snakes with broken rattles having no taper, there is just no way to know how many segments are missing.

So how long can rattlesnakes live? Decades! I have personally kept some southern California species in captivity over twenty years. The Splash Education Center at Mather Field has a healthy Northern Pacific Rattlesnake that has been in captivity for a well-documented 32 years! But how long they survive in the wild is a much different question. Captive snakes do not have to contend with coyotes, hawks, owls, king snakes, temperature extremes, and all the other hazards of a natural existence – not to mention humans and their cars. While references like Robert Stebbins’ Field Guide to Western Reptiles and Amphibians (2003; Houghton Mifflin Co.) list the maximum size of our northern California species as over five feet, the fact is that three-footers are now uncommon. Large rattlesnakes have become very rare all over the United States, with individuals approaching old record lengths almost never found. Of course, in some remote wilderness where people rarely visit (if there is such a place today!), maybe there are still a few very large wild rattlesnakes…