Spring emergence has begun!

It took only a few days of moderately warmer weather to stir our sleeping rattlesnakes. I haven’t downloaded my temperature logger recently but it has been easy to notice that it’s in the 50s instead of the 30s the past few mornings, while daytime highs have been in the high 60s.

And today, we found some rattlesnakes stirring. Until now, the body temps of all of the hibernating rattlesnakes have been in the single digits Celsius (less than 50F). Earlier today, ten of twelve telemetered rattlesnakes were in double digits despite a full thick overcast. Male 37 – still inaccessible on the bluff – produced a calculated body temperature of 21C (70F). (The bluff is always warmer because it is steep and faces south, so solar energy is more concentrated per unit of surface area.) Male 37 is clearly no longer deep underground.

Next was Male 46 at 16C (61F) and, sure enough, he was peering out from under the log where he spent the winter.

Male 46 around midday today, 10 March 2017, peering out from under his log.

When we arrived at Female 41’s radio signal, we found a rattlesnake laying out in the grass and assumed it was her. The rattle was not clearly visible at the time but later examination of photographs disclosed white/green paint in the rattle. Female 41 is white/blue and the rattlesnake we observed turned out to be Male 49, marked and released without a transmitter exactly two years ago today, on 10 March 2015! Female 41 was very close but out of sight.

Close examination of photographs proved this snake to be Male 49 (white/green), not Female 41.
Male 49, as we first observed him; 10 March 2017.

We also found Male 40 laying out in the same spot as last week (see the blog post on 6 March), plus we found a new animal laying in the grass next to another large log where two telemetered adults have been napping since last fall. He (or she) was captured and, while too small for a transmitter, will be measured, marked, and will donate a blood sample before being released as CROR81.

More news to follow!

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.

The 2016 rattlesnake season is underway

After some limited basking by a couple of telemetered rattlesnakes and short movements by Female 41 and Male 49 two weeks ago, the return of cool cloudy weather sent these animals underground again. Then, despite several days of sunny weather last week, the rattlesnakes remained cool and out of sight – with the exception of Male 49. While Female 41 stayed underground and cold, he napped most afternoons in the sun just a couple feet away.

But yesterday, everything changed. Males 37 and 38 who spent the winter near the top of the bluff had moved down; one was out of sight under a log and the other was in an ambush coil in the grass under a small fig tree.

CROR38, first sighting of the year; 29 February 2016 Original RAW IMG_0195.CR2
My first look at Male 38 this year. He appeared to be hunting at the base of the bluff, just a few dozen yards from where he spent the winter on the hillside.

A rapidly pulsing transmitter told me before I arrived that my underweight geriatric Male 40 had survived another winter and was in the sun at his winter shelter.

CROR60 at RFG02, first 2016 sighting; 29 February 2016; Effie Yeaw Nature Center Original RAW IMG_0177.CR2
My old friend, Male 40, made it through another winter. Over two seasons, he has moved very little and I have never found him courting a female. This is my first look at him this year. He had a body temperature of 88F when this photo was taken. Although he may have had more surface area exposed to the sun before I arrived, it takes very little exposed skin to dramatically raise their body temperature on a sunny windless day.
Non-telemetered Male 49 (foreground) and telemetered Female 41 (background)
Male 49 (foreground, no transmitter) and telemetered Female 41 (background). Female 41 was underground with a body temperature of 52F on Sunday but had a body temp of 86F when this photo was taken yesterday (24 hours later).

Female 41 was in the sun with Male 49 laying partly on top of her, although I saw no active courtship during my brief visit.

Other telemetered snakes had moved short distances but were out of sight when I was there yesterday. But in my travels, I also sighted five unmarked rattlesnakes basking, including a beautiful little female sporting a food bolus about the size of a vole – so she has already fed successfully.

So for the next three months or so, females will be trying to eat as much as they can to nourish their next brood while males will be wandering all over the place (and hunting less) in search of receptive females. It is during this time that male rattlesnakes tend to turn up in yards and on trails, producing interactions with people.

Remember that rattlesnakes want nothing to do with something the size of a person. Leave them alone and they will be happy to avoid you, too!

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!


Pregnant females, injuries, and shedding

First a quick general update: Spring courtship seems to be over; I have not seen a courting pair since 16 May. Since the end of May, the pregnant females have taken up refuge in ideal shelters where they can thermoregulate optimally. Females 39 and 41 are now in the same shelters where they gave birth last year (but not together) and Female 47 is with 39. Female 54 is by herself and has not moved since we implanted a transmitter and released her on 23 May. Neither 47 nor 54 were telemetered last year so I have no history for them. These soon-to-be mothers are all maintaining body temperatures within a couple of degrees of 30C (86F). The males and Female 53 (not pregnant?) have been hunting, mostly hanging around California ground squirrel burrows for the past month as the squirrels produce the first pups of the season (more on hunting ground squirrels) and the body temperatures of these foraging snakes has varied widely compared to the pregnant females (more on body temps).

In my last post, I showed you a photo of an unidentified rattlesnake in the refuge with Female 41 – the same refuge where Females 41 and 43 had babies last year. (You may remember that Female 43 was found dead at the refuge last October; click here for that account) While I could only see the new snake’s nose and a small area of flank at the first encounter, I saw her twice more over the next eight days. She was shades of dark brown, while Female 41 is quite pretty with chocolate brown dorsal blotches on a gray background. During the subsequent two sightings, I could also see the new animal’s rattle, which was long and unbroken (i.e., she still had her birth button). Then a week ago, I found Female 41 and the new rattlesnake basking next to each other and was able to capture the new animal (CROR55).

The first thing I noticed was that she was pre-shed. That is, her eyes and new rattle segment were milky white (more about shedding below). The next important discovery was that she is, indeed, a female – and quite heavy…maybe pregnant. A photo of her snout (bottom photo, below), when compared to the nose in the photos of the unidentified rattlesnake on 3 June (top photo, below) confirms that she is the same animal.

unidentified Crotalus oreganus under log at Refuge 03 on 03 June 2015, Effie Yeaw Nature Center Origonal RAW IMG_7382.CR2

I have numbered some landmark scales in these photos that you can compare but also compare the size and arrangement of surrounding unnumbered scales. And while the fine pigmentation of the individual scales is obscured in the pre-shed photo, I have circled some larger pigmented areas that are visible. Keep in mind that the photos were taken from slightly different angles, making some scales that are visible in one hard or impossible to see in the other. The size, number, and arrangement of nose and crown scales on these rattlesnakes are a bit like fingerprints on primates: they are individually unique, so far as we know. Also note the whitish eyes and how the scales on her nose appear a bit swollen in the pre-shed photo.

As I examined her further, I made another interesting discovery: she has sustained a serious injury to her abdomen sometime in the past. Although well healed now, her skin is scarred on the dorsal midline 575 mm (23 in) from her nose (her body length, excluding tail [snout-vent length or SVL] is 720 mm [28 in]). Furthermore, her body is noticeably narrowed at the scar (photo below) and her abdomen is hard and dense to the touch for several inches on both sides of the scar.

Female CROR 55 Original RAW IMG_7555.CR2

Nonetheless, she looks and acts healthy and might, indeed, be pregnant. I could feel two masses in her anterior abdomen that were consistent with fetuses but could not differentiate anything posteriorly where her abdomen is apparently scarred internally. She would normally be a great transmitter candidate but I elected to release her without one because of the suspected internal scarring where the transmitter would be implanted, plus I did not want to damage her skin as she prepares to shed.

This brings up the point that life is not easy for these snakes. In addition to this healed injury to Female 55 and the death of Female 43 last year, you may remember that I processed and released a small male (CROR44) early last December that had recently sustained some significant trauma from a predator, including a deep penetrating abdominal wound that I suspected would prove fatal over the winter (more details). While processing Male 52 early last month, I removed a “foxtail” (a seed from one of the non-native Bromus grasses that blanket the preserve) from his cloaca (cloaca defined). This little floral harpoon had not yet caused much damage but I don’t know what would have prevented it from burrowing into his abdomen and causing a potentially fatal injury. My point is that these rattlesnakes, despite their formidable reputation, are susceptible to constant hazards.

Shedding (the technical term is ecdysis) is the sloughing or molting of the outer epidermal layer (the stratum corneum) in scaled reptiles. This corneal layer is a matrix of keratin (the same material as your hair and fingernails – and the rattlesnake’s rattle!) infused with lipid (fat) molecules that greatly slows the passage of water through the skin. Because this matrix is acellular (contains no cells), it cannot grow. Thus, as the snake grows, this layer must be replaced periodically. When the time comes, the snake’s body produces a new corneal layer under the old one. This creates the blue or whitish tint, most notable in the eyes. In rattlesnakes, a new segment is produced at the base of the rattle during each shed, which is also whitish at this stage. Once the new corneal layer is ready, the snake’s body secretes fluid between the old and new layers, separating them and softening the old one. When this fluid is secreted, the whitish color disappears (the eyes clear) and the snake is ready to shed. They then rub their face on any available surface and start to peel back the old layer from around the nose and mouth (photo below). They continue rubbing, eventually crawling out of the old “skin,” leaving it inside-out, usually in one piece.

A 10-day-old Northern Pacific Rattlesnake beginning his post-partum shed while being processed during my El Dorado Hills field study.
A 10-day-old Northern Pacific Rattlesnake beginning her post-partum shed while being processed during my El Dorado Hills field study. (Also note the “birth button” at the end of her tail)

I’ll leave it there until next time, when I’ll explain rattle growth and trying to estimate age from the rattle.


The effect of drought on rattlesnakes

Field studies of rattlesnakes indicate that they cease most movement when water stressed and remain in their established home ranges, rather than migrating into developed areas in search of water, despite frequent claims to the contrary.

In my last post, I mentioned witnessing Females 41 and 47 feeding, as well as finding new Female 53, who was very heavy and likely pregnant. Since then, I have come across Female 41 eating another vole, found another new female (#54) that is heavy and definitely pregnant, and come across a fat but unidentified rattlesnake in the refuge where Females 41 and 43 had babies last year. I could only see the face and a bit of a flank of the unidentified animal (photo below) so I couldn’t even determine sex.

unidentified Crotalus oreganus under log at Refuge 03 on 03 June 2015, Effie Yeaw Nature Center Origonal RAW IMG_7387.CR2

It could be a male that has just eaten a ground squirrel pup – but it is more likely another pregnant female. We now have five telemetered females (39, 41, 47, 53 and 54) and all are in great shape, with three either confirmed or likely pregnant and the others in good shape to reproduce although I have not yet had my hands on them this year to palpate for fetuses.

This brings up a timely point: This will obviously be a good year for rattlesnake reproduction in our area, despite being in the midst of an historic drought. Since the news media often quotes “experts” claiming drought “drives rattlesnakes out of the hills and into yards looking for water,” this is a great opportunity to set the record straight about how drought affects rattlesnake movement.

We live in a Mediterranean climate, historically characterized by warm dry summers and cool wet winters. Even during years with “normal” precipitation, vast tracks of mountains, foothills and many valley areas have no surface water between late spring and the return of winter rains in November or December – yet they support healthy populations of rattlesnakes. Herbivores (insects, rodents, etc.) get most of their water from the plants they eat and rattlesnakes get water from eating the herbivores. The bodies of terrestrial vertebrates are usually composed of 65–75% water, so eating a 100 gram (3.5 ounce) rodent is like drinking about 70 grams (2.5 ounces) of water for a rattlesnake (plus the nutrients and energy gained). Make no mistake, rattlesnakes suck droplets from various surfaces, including their own skin, deposited by rain and dew (photo, below) and they will certainly drink from standing water when it’s available. But especially during summer and fall, these other sources are not available and virtually all of the water a rattlesnake needs is obtained from its prey.

adult Crotalus s. scutulatus (Mohave Rattlesnake) drinking rain water near Apple Valley, San Bernardino County, California, USA [wild animal, in situ]
Mohave Rattlesnake drinking rain water from its own body. [Cardwell, M. D. 2006. Rain-harvesting in a wild population of Crotalus s. scutulatus (Serpentes: Viperidae). Herpetological Review 37:142-144.]

Rattlesnakes are models of low energy physiology. As ambush predators, they move comparatively little and rely largely on anaerobic metabolism. Their sedentary lifestyle combined with the corneal layer of their skin (full of water-blocking lipids) dramatically lowers the amount of water that passes into and out of their bodies – known as “water flux.” Nonetheless, multiple studies have shown that the most significant mechanism for water loss in terrestrial snakes is evaporation, with about 75% being lost through the skin and the remainder via exhaled breath.

During my four-year field study (2001–2004) of Mohave Rattlesnakes in southern California, I was able to compare behavior, including average daily movement and reproductive effort, between the severe drought year 2002 and 2003–2004, when rainfall returned to average or above average. I found that average daily movement during 2002 was less than one third of 2003–2004 averages. And while I encountered dozens of courting pairs during the two non-drought years, I observed a male courting a female on only one occasion in 2002. Yet these rattlesnakes continued to eat at a rate indistinguishable from the non-drought years, based on scats deposited in holding containers and later analyzed. These snakes were reducing exposed surface area (and, therefore, evaporative water loss) by remaining coiled and immobile, covering much of their skin within their coils. They even buried their coils partially in loose soil at times, covering additional skin area. Remaining stationary eliminated their ability to find and court mates but, as sit-and-wait ambush predators, it allowed them to continue to hunt – and obtain the body water of their herbivorous prey. They also positioned themselves behind vegetation and ground contours in 2002 to avoid wind and sun, both of which increase evaporation rates. You can find more details in my MS thesis.

We have seen similar behavior in Northern Pacific Rattlesnakes in recent years at my El Dorado Hills study site, where the rattlesnakes remained tightly coiled and stationary in deep chaparral on north-facing slopes during particularly hot dry summer weather. At Effie Yeaw, all of the rattlesnakes caught by staff around the ponds during the past year, as well as the telemetered rattlesnakes I have found there, have been males found during the courtship season. The females have remained in the woods, away from water sources. While the snakes will drink when they find the ponds (or other water sources), that’s not why the males are there… they’re wandering around looking for females! And, yet, the females are now fat and pregnant.

Drought probably does not affect rattlesnake movement until it becomes locally severe, as it did at my Mohave Rattlesnake study site in 2002. When the snakes start to become water stressed, they don’t set out into uncharted territory looking for surface water. Rather, they stop moving and hunker down where they can best reduce evaporative water loss while still striking any prey that wanders by. Currently, if the preserve at Effie Yeaw Nature Center is any indication, there is lots of annual plant growth and the vole and ground squirrel populations are thriving – and so are the rattlesnakes.

So when people find a rattlesnake in their yard during a drought, the most likely explanation is that it is a male looking for receptive females and the drought is not severe enough locally to stress the rattlesnakes. When they are truly water stressed, rattlesnakes move less – not more – than usual. Unlike most large mammals that have much higher metabolic and water flux rates and require standing water to drink, there is no evidence that rattlesnakes leave their established home ranges looking for water, despite the popular belief to the contrary. They do just the opposite.

More feeding, courting, and a new female

The first thing I encountered early in the afternoon of 13 May was a dead adult rattlesnake in the grass behind the Visitor Center. The carcass had completely putrefied and had been eviscerated by insects. It was an average-sized adult and had no paint in its rattle (i.e., it was not one of our study animals). I could not determine the sex. The head and rattle were intact, indicating it was unlikely a human had killed it. There was no obvious evidence of trauma elsewhere, either, but it was in such bad shape that it was difficult to tell. People often ask about the life expectancy of rattlesnakes and the answer is that, in captivity, they have been known to live more than 30 years. But in the wild, if they make it to adulthood (which few do), they are constantly threatened by raptors, coyotes, kingsnakes, people and their cars, temperature extremes, and other hazards. My guess is that few make it to ten years.

About 3 PM on the same day (13 May), I found the radio signal from Female 41 coming from dry grass on the hillside near the stairs on the trail behind the amphitheater. When I refined her location and parted the grass, I found her swallowing a small rodent – which she immediately spit out (this is common defensive behavior, as rattlesnakes are defenseless when swallowing prey). I had to remain completely still for five minutes or more before she decided it was safe to eat again. Because she was so deep in the grass and I had only a small opening through which to view her (photo below), I could not tell exactly what kind of mammal she was eating. It was uniformly gray with very fine fur, a gray belly, and was about mouse-sized. It was too large for a shrew and the lack of a light-colored belly ruled out most native mice. The dorsal fur looked too fine for a vole and I could not see the tail. What I could see looked like a house mouse, Mus musculus, but we will never know for sure as I did not want to bother her further and be the cause of her abandoning her kill.

adult female Crotalus oreganus (CROR41, in situ) swallowing an unidentified rodent (Mus or Microtis) at Effie Yeaw Nature Center on 13 May 2015 Original RAW ING_7074.CR2

When I next visited her two days later, she had moved only a few feet and was coiled next to a California Ground Squirrel burrow, which she retreated into when I arrived. This was the first time this season I have found a rattlesnake close to or in a ground squirrel burrow. I haven’t seen ground squirrel pups yet but I saw a pregnant female on 11 May, so I suspect there are pups in burrows by now and the rattlesnakes hunt the pups heavily in spring and early summer. (Click here and scroll to the bottom of the first page for more info on the fascinating interaction between Northern Pacific Rattlesnakes and California Ground Squirrels)

With all of our telemetered rattlesnakes alone and apparently hunting (and not having found a courting pair since 20 April), I was beginning to wonder if courtship might have concluded early this spring. But on 16 May, I found Male 38 on top of an unmarked female next to the large log in the meadow. She was heavy, healthy, and had no paint in her rattle – a beautiful rattlesnake, but she was also quick! As so often happens, the courting male was far less afraid of me (too much testosterone?!?!) than the female, who fled immediately and made it under the log before I could capture her.

I wish that people who fear rattlesnakes and think they are so malevolent could see how these animals really react to being approached by a person. If I had been able to catch all the unmarked rattlesnakes that have escaped from me this spring, our quota of seven males and seven females with transmitters would be full… but they are shy and very quick to flee into the grass, wanting nothing to do with something as big as a person. Remember, in their tiny primitive brains, rattlesnakes react to encounters based on three criteria: Can it eat me? Can I eat it? Can I mate with it? Clearly, we fall into the first category!

On 19 May, I found Female 47 in the meadow a little after 10 AM, crawling slowly through the grass, carefully tongue-flicking as she moved. I took a few photos and she crawled out of sight while I recorded my standard data. But when I started to depart, I came across her a couple of meters away with an alligator lizard, Elgaria multicarinata, in her mouth. She retreated a short distance to a small shrub with the lizard still in her mouth and, after I stood motionless once again for several minutes, she began to swallowed it (photo below).

Female Northern Pacific Rattlesnake (Crotalus oreganus; CROR47; in situ) eating Southern Alligator Lizard (Elgaria multicarinata) at Effie Yeaw Nature Center on 19 May 2015. Original RAW IMG_7254.CR2.

Two days later, while searching for Male 35 on 21 May, his signal led me to a large and very dense thicket of armpit-high Milk Thistle (Silybum marianum) in the meadow. I have avoided penetrating this thicket when various males have occasionally visited it this spring because the spines go right through all clothing and there is just no way to avoid them. But on this cool morning, when I peered over the thistle into a little clearing in the thicket, I saw a nice unmarked rattlesnake laying in the grass, probably hoping the clouds would clear and allow some sun to shine through (photo below).

CROR53 in situ at capture site. Original RAW IMG_7320.CR2

Hoping that she was a “she” and probably the reason that Male 35 was also in the thicket, I carefully retreated without spooking her and dropped all my gear in the grass except a cloth bag and snake hook. Stepping into the sea of spines, I slipped the snake hook under her and began to gently lift her before she reacted. I almost got her clear of the thistles before she wriggled off the hook but I was able to quickly catch her again before she completed her escape. Once clear of the thistles and in the dry yellow grass, she could no longer hide and I had her in the bag shortly thereafter.

Her sex was later confirmed and she became CROR53. (Click here for an explanation of CROR). She was very heavy for her length and full of shiny white abdominal fat when I implanted the transmitter. I could not be sure of her reproductive condition because of so much material in her bowel; she clearly had been feeding very successfully. Reproductive condition is determined by palpating her belly through her belly scales, feeling for yolk masses and, later in the season, for embryos. Because the transmitter incision is less than 3/4 of an inch long and made on the side, two scale rows up from the end of the belly scutes, it doesn’t help in determining reproductive condition. When she was released the morning after her surgery, she became our fourth telemetered female, along with four telemetered males (plus two additional males with failed transmitters I am still hoping to recapture). I am up to 413 recorded encounters with EYNC rattlesnakes this year… we are off to a great start!

Soon to come: an explanation of shedding and rattle growth.

Copulation & a malformed rattle

Just a quick entry regarding two very interesting recent observations:

First, just in case you were wondering what rattlesnakes do when they first warm up after a long winter’s nap… I came across this copulating pair early this afternoon. What you see in the photo (below) is almost all I could see. Most of their bodies were hidden in the deep grass. The elevated tail is the female’s and the male’s tail is wrapped under her cloaca. You’ll notice that neither rattle contains any paint; they were (and remain) unmarked snakes. I didn’t disturb them!Copulation 18Mar15

Also, the most recent animal to be processed and released at EYNC was a small (554 mm/22 inch) female with a deformed rattle (below). These are pretty rare. It looks like a congenital deformity rather than being the result of trauma. One additional segment clings to the terminal one and the snake can make a little buzz but I am sure she is incapable of accumulating a string of segments. The lesson here is that even in the rare event of a deformity or amputation, no rattlesnake has a long tapered tail like California’s harmless snakes.Rattle_CROR50 18Mar15


16 March: General emergence has occurred!

The day after I saw Male 37 in the flat woodland (7 March), down from his winter shelter on the hillside, Male 38 was found about 10 meters (33 ft) from his hibernaculum, where he remained coiled in the grass for several days while basking when possible. Although other telemetered rattlesnakes remained at their winter shelters for most of last week, they were often found basking in the sun, as were several unmarked rattlesnakes.

I caught and marked several of those new basking rattlers and, as it appeared that another cold snap was unlikely, I implanted transmitters in CROR46, captured on 6 March, and in a new female, CROR47, captured a few days later. I could not palpate any fetuses in Female 47 and I don’t think she is pregnant but it’s possible, as it is very early in the year.

As of today, Female 41, who produced kids last season and apparently hibernated by herself, was coiled in deep green grass about 30 yards from where she spent the winter (below), apparently hunting. CROR 41 16Mar2015AMale 35 was coiled in deep grass under a live oak tree he frequented last year. He’s the one who spent so much time in the vegetation near the bike rack, silently welcoming guests much of last summer. We’ll see where he goes next.

You may remember that Male 40’s transmitter was the most recent to fail prematurely. Well, I was able to recapture him today. I also recaptured Male 38, who’s transmitter is still working but is part of the batch that have been failing early. Both will be released with new transmitters in the next day or two. Males 36 and 37 remain on the loose with failed transmitters.

Finally, Male 46 and Female 47 have found each other and were laying in the sun together this afternoon (below). There was no active courtship when I saw them (they were very still) but I’m not buying that this is a platonic relationship this time of year!CROR46 & 47_16Mar15

As you can see from the photos, these rattlesnakes are almost impossible to see in the thick carpet of green grass that covers the park now. And when approached too closely, they disappear silently into the grass – as Female 47 did as soon as I tried to get closer after the photo above. Of course, the green grass makes it very easy to step on a rattlesnake!

As of today, Female 39 is the only telemetered animal that has not left her winter shelter, although her body temp has been warm (indicating she has been basking, although I haven’t seen her) and, several days ago, she moved to the other end of the log where the location of her radio signal was identical to that of Male 35 for a couple of days before he left. Hmmm…!

I also heard two different California ground squirrels incessantly chirping their alarm call this afternoon. When they are signaling a hawk or coyote, they usually chirp once or twice and dive for cover. When they continue to chirp over and over, it is often a snake (unlike a hawk or coyote, once they discover a snake, they can avoid it without going underground). Unfortunately, I didn’t have time to investigate today.

7 March 2015

There’s lots to report during the past 1.5 weeks…

On February 26, I came across another unidentified young adult rattlesnake at the refuge where so many others appear to have spent the winter. He or she was basking in the sun but escaped into the refuge, showing me in the process an unbroken rattle of about 7 segments with no paint. No time for photos, either. No other snakes were found basking that day.

I found Male 38 and Female 41 basking in the late afternoon on both 1 March and 3 March. Their body temperatures were 70F & 86F, respectively, on 3/1 and 84F & 90F on 3/3.

On the afternoon of 6 March, Female 41’s body temperature of 86F indicated she had been basking earlier but she was out of sight when I looked for her. By comparison, body temps for animals that have not basked recently have been around 10-14C (50-57F). While I did not find any of the marked snakes visible on 6 March, I did find a new male basking and captured him – CROR46. He has an unbroken rattle of 8 segments, making him relatively young but, at 264 g (9.3 oz), he is a good candidate for a transmitter. I will have to research the extended weather forecast for our area and if another cold snap looks unlikely, he will get a transmitter. I will also photograph his face and compare him to the unmarked snake photographed at this refuge on 14 February.

Just after 10 AM today (7 March) I found Female 41’s radio signal (her transmitter is not from the problem batch) rapidly increasing in pulse frequency, indicating she was cool but warming rapidly in the sun. Unlike some of the other basking rattlesnakes in the area, I have never found her basking in the open, out from under cover; she only exposes a small part of her surface area to direct sun while remaining sheltered. Take a look at the photo below and note how little of her was in the sun, yet her body temperature increased from 48F to 59F as I monitored it over just 20 minutes!

CROR41 basking Original IMG_5509.CR2

Finally, I spent some time around midday today checking some the favorite places for Males 36 and 37 – both are carrying dead transmitters. Surprisingly, I came across an adult rattlesnake at the base of the hill where both hung out last year. The snake was only partly exposed, with head and anterior body already in a hole and its tail hidden in the grass. Just as quickly as I saw it, it continued down the hole but not before I could clearly make out Male 37’s yellow/red rattle markings. Although I couldn’t capture him (without tearing up the environment, which I won’t do), he was 32 m (105 ft) from his winter refuge high on the hillside… so spring emergence is definitely underway! I have been told by several other people of recent rattlesnake sightings but this is the first of our study animals to be found away from his hibernaculum this year.