The first of our four pregnant rattlesnakes has given birth since last Thursday (between September 8 and 12).
The animated GIF file above shows Female 54 in the foreground inside a hollow log and still pregnant (note the scales pulled apart on her abdomen) but with babies crawling over her on both sides. Female 39 is in the background and no longer pregnant. Since these are the only two females I have seen gestating in this hollow log this year, I believe the kids belong to Female 39. The video was recorded with our BurrowCam, actually a Ridgid Tools inspection camera that can be inserted up to three feet into burrows, logs and other narrow chambers.
As you know if you have been reading this blog for very long, mom and babies stay together for a week or a little longer, until the kids shed the corneal layer of their skin for the first time. After that, they go their separate ways to forage for food before hibernation. Thus, if my telemetered females are in sync with the larger population, baby rattlesnakes should begin appearing on the trails around the fourth week in September.
This is Female 39’s third brood in four years. Each time she has reproduced since I have been monitoring her, she has made a beeline to the same spot in the blackberry thicket on the other side of San Lorenzo Way as soon as the kids leave home. Apparently fall rodent hunting is very good there! We’ll see if she stays true to form this season.
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.
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.
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:
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 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.
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 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 on top of her on 29 August 2016. Note his tail wrapped around and under hers.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.
Well, we are entering that time of the season when we can expect to find baby rattlesnakes any day now. Of course, the youngsters will not be roaming around where they might encounter people for about 10-14 days after birth…so we usually don’t encounter them on trails and in yards until early September.
But our six telemetered females are displaying a variety of behaviors indicating that all may not be about to produce babies. Six weeks ago I reported that Females 39, 41, and 53 were all pregnant and in the gestation shelters they have used repeatedly to thermoregulate before giving birth in previous years. Furthermore, I could feel six fetuses in Female 80’s belly when I implanted her transmitter in June.
Since that mid-July report, Females 39 and 53 have behaved predictably for expecting moms, remaining in their gestation shelter, and both appear to be about to produce kids. In the photos below, note the abdominal girth of these females, with scales pulled widely apart.
Female 39 in her gestation shelter on 20 August 2016 – the same shelter she has used to incubate her kids for three years in a row. Her body temperature at the time of the photo was 32C (90F).Female 53 in a different part of the same hollow log as Female 39 on 20 August. Female 53’s body temp was 30C (86F).
This will be the third consecutive year that Female 39 has produced offspring and the second for Female 53, so far as we know. We were not monitoring them previously. Between the first of July and yesterday, 23 August, the average body temps for Females 39 and 53 have been 28C (82F) and 29C (84F), respectively.
Six weeks ago, Female 41 had just returned to the gestation shelter she used the previous two years, which led me to believe she was likely pregnant again. However, after staying only three weeks, she left and has been spending her days mostly out of sight in various ground squirrel burrows during August. I have not been able to get a good look at her in recent weeks but her behavior and average body temperature of 26C (79F) suggest that she may not reproduce this year. Although Female 41 produced kids in both 2014 and 2015, I want to remind readers that skipping a year or two between broods is far more common than annual reproduction for temperate-latitude pitvipers.
Our remaining three telemetered females are new to the study this year, so I have no data from previous years. Female 66 has behaved quite normally for a non-reproductive year: hunting continuously throughout the spring and summer. Her July-August average body temp has been 22C (72F).
Female 66 in a typical ambush coil in late May. She continues to move around and hunt during July and August.
Female 75, however, appears ready to produce babies, although she has been moving back and forth frequently between two ground squirrel burrows 17 meters (56 feet) apart. Her average body temperature during July and August has been 27C (81F).
Female 75 on 23 August, illuminated by sunlight reflected from a mirror. She is a few inches inside one of the two ground squirrel burrows she has been occupying in recent weeks. Again, note the distended abdomen with scales pulled apart. Body temp was 27C (81F) at the time of the photo.
Finally, there is Female 80. When I captured her and implanted her transmitter in June, I could clearly feel six fetuses lined up in her abdomen. Shortly after I released her at her capture site near the base of the bluff, she climbed up the hillside and has remained near the top ever since. On three occasions, I have climbed that steep, loose, and treacherous slope but have failed to locate her. Her radio signal seems to emanate from thick ornamental ivy growing down from a residential backyard under fig and valley oak trees. She is also just above an underground wasp nest. Just to be clear, I am far more comfortable with rattlesnakes than a nest of wasps – especially where I cannot easily run away! Since I have no previous data from her, she could be in her usual gestation shelter. However, her July-August body temperatures are not consistent with a gestating female, with an average of 23C (73F). I’m not sure how this is going to play out…
Just for comparison, the seven telemetered males have been moving around a lot, hunting and occasionally hanging out with the pregnant girls for a day or two at a time. Their average July-August body temps range from 17C (63F) to 26C (79F), with the average between the boys of 23C (73F). Note how closely these data match non-reproductive Female 66’s average body temp of 22C (72F) during the same period.
A big impressive rattlesnake at over 38 inches and about 1.5 pounds (last October), Male 37 ignored us yesterday as he crossed the trail in front of me and an EYNC visitor with whom I was chatting. The visitor was quite impressed and I never tire of watching these amazing and interesting animals with such an undeserved reputation for aggressiveness!
That’s it for now. Next post will almost certainly be (cute!?!?) baby pics!
