What a confusing spring!

March weather had the rattlesnakes along the American River Parkway confused! As I have mentioned before, the rattlesnakes usually emerge and begin to bask when the average temperature at ground level remains at or above about 50F. They are usually deep enough underground during the winter to escape daily high and low fluctuations, so it is the average that eventually penetrates to them and signals that winter is likely over. But not this year.

Most telemetered rattlesnakes emerged in March but remained at their hibernation sites, basking on sunny days as they usually do before leaving their winter shelters. But rather than getting drier and warmer, the weather throughout April was a constant mixture of rain and cloudy cool days and nights. Of the few rattlesnakes that left their winter hibernacula, two returned while others became inactive at other sites. The rattlesnakes do just fine in the rain. In fact, they drink rain and dew when it’s available. And cloudy weather is not a deterrent to activity if it is accompanied by warm temperatures. But nighttime air temperatures below 50F followed by overcast cool days are not good for activity in animals like reptiles that depend on the environment for their body heat.

So, in late March and throughout April, the few stretches of several sunny days with relatively warm nights in between produced some sporadic rattlesnake activity. But it was not until the end of April that more consistent sun and heat produced vigorous widespread rattlesnake activity.

A courting pair of rattlesnakes on 28 March, next to the log under which they spent the winter. The male is on top of and mostly obscuring the female, which is paying no attention to him.

As expected, when we had activity, we observed lots of courtship. This is, after all, the peak of courtship activity, followed by almost no reproductive activity from June to mid-August before an untick in courtship again in the fall.

But by far the most interesting discovery this spring was by one of my UC California Naturalist students who found a small male rattlesnake with no rattle! (See photos below) Now I hesitate to mention this, for fear of starting a panic about rattleless rattlesnakes. Please remember several things:

  1. Rattlesnakes missing their entire rattle are extraordinarily rare. So rare, in fact, that they usually rate a note in a biological journal. This one will!
  2. No rattlesnake has a long pointed tail like our many harmless snakes.
  3. Rattles can be missing due to either injury or genetic mutation.
  4. This little snake appeared to be recently missing the end of his tail and had other serious but healing injuries. Apparently a close call with a predator!
  5. Identify rattlesnakes by looking at the tail! Yes, rattlesnakes have elliptical pupils and heat-sensitive facial pits but some harmless snakes have elliptical pupils and both these characters are too small to be clearly seen from a safe distance (two-times the length of the snake). Some harmless snakes also have rather triangular heads, especially when they have been frightened and are behaving defensively. But no rattlesnake has a long pointed tail like our harmless snakes and all of California’s dangerous snakes are rattlesnakes.

Check out the following images…

Our rattleless Male 87, on the day of his capture, 09 April 2017. He is only about two feet long. Note that his appearance is “rattlesnake” in every way except for the stump of a tail without a rattle.
Close-up of Male 87’s tail.
Dorsal x-rays of Male 87’s tail (right), compared to a normal rattlesnake’s tail (left). The large opaque “club” in the normal tail is the calcified stylus inside the tail to which the shaker muscles attach (the hollow keratinized rattle on the normal tail is present but invisible to the x-rays). Many thanks to Hazel Ridge Veterinary Clinic for the radiograph.
One of several other healing injuries on Male 87. (The scale is centimeters; 2.54 cm = 1 in)
This is a harmless but badly frightened gopher snake that has just been stepped on by a hiker. Note how it has flattened its head into a triangle. It was also vibrating its tail in the grass, producing a good imitation of a rattlesnake. But a look at its tail reveals that it is not a rattlesnake (see next photo) and, therefore, a harmless California snake.
No rattlesnake has a long pointed tail like this gopher snake.

To be sure, there are dangerous snakes in other parts of the United States that have long tails without rattles (cottonmouths, copperheads and coral snakes, in southern and eastern states). But in California and other northwestern states, the only dangerous snakes are rattlesnakes.

Look at the tail to identify rattlesnakes!

 

 

And, yes, Male 87 was processed and released, just like all the others. While he has no paint in his rattle, he won’t be hard to recognize!

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!

Where are the rattlesnakes?

Well, it’s March and many recent days have been sunny and quite warm. Even though daytime highs have been listed in the 50s, that’s measured in shade and the temperature in the sun near the ground is always considerably warmer. So why were rattlesnakes basking in good numbers by late February last year but not yet this year?

There are two parts to the answer. First, most of the snakes spend the winter deep enough underground that they are insulated from daily temperature fluctuations. In other words, they do not feel daytime highs or nightime lows. Deep in their winter shelters, the temperature creeps up or down gradually in response to the mean (average) outside temperature. The second part of the answer is that natural selection tends to remove animals from the gene pool that don’t spend the winter deep enough and/or that venture out too early and get caught in freezing weather. The animals that select optimal winter shelters tend to live longer, and thus produce more offspring carrying the genes for those successful behaviors. (For those of you interested in the evidence for genetic influence on behavior, Time Love and Memory (2000) by Pulitzer Prize winning author Jonathan Weiner is an entertaining and astonishing summary, written in easy-to-understand language but with references to the scholarly research.)

So how do we know the temperature in the underground shelters?

Besides having recorded hourly temperatures for nearly four years with a data logger in a burrow 1 meter (39″) below ground in the Mohave Desert during a previous study, we can routinely calculate body temperatures of the hibernating snakes from the pulse interval of their transmitters during the winter.

The transmitters come from the manufacturer (Holohil Systems Ltd.; www.holohil.com) with a calibration graph showing the correlation between pulse rate and temperature for each transmitter (they vary slightly).

A standard conversion graph supplied by the transmitter manufacturer, Holohil Systems. Put simply, the transmitters beep faster when warm and slower when cool and at a predictable rate.

I routinely check the pulse rate in a water bath at room temperature before implanting a transmitter and adjust the mathematical conversion, if it differs slightly from the factory data. Then it is a simple matter in the field to time the pulse interval with a stopwatch and convert that measurement to temperature later. And since the transmitter is implanted inside the snake’s abdominal cavity, transmitter temperature equals core body temperature.

I also record hourly shade air temperatures with a data logger in the nature preserve at Effie Yeaw Nature Center. This gives me a standard local reference against which to compare rattlesnake behavior and look for correlations with weather conditions.

My data logger is located on the north side of a large cottonwood tree near the center of the EYNC nature preserve where it is never exposed to direct sunlight.

I can then compare rattlesnake behavior, body temperatures and air temperatures. This is especially interesting when one year is compared to another.

Some early temperature data for 2017. Note that the daily mean air temperatures vary greatly, depending on weather conditions, while the mean rattlesnake body temperatures tend to be nestled within the fluctuating air temps. These snakes were still underground and not affected by daily high and low temperatures outside.

You can see about six weeks’ data from this year in the chart above. The fluctuations in mean (average) air temperature (open circles) reflect the daily changes based on cloudy verses sunny days and cold air masses moving through verses warmer southern air (the same factors discussed every day by meteorologists).  The five filled circles are the mean body temperatures of the twelve telemetered rattlesnakes on the days that I recorded their data. There are more air temperature records because the data logger records automatically around the clock while rattlesnake body temperatures are only recorded when I visit the study site (which I do less frequently when the animals are inactive).

Now take a look at the corresponding data from last year:

Early temperature data for 2016. In these data, you will see that mean body temperatures are not buried among the mean daily temperatures. Rather, especially by the middle of February, the mean body temperatures greatly exceed the mean air temperatures. That’s because the animals were out of their shelters and basking in the sun.

Checking my behavioral observations from last year, I find a few rattlesnakes were starting to bask occasionally by the end of January and most were basking regularly on sunny days by the end of February. Regular basking continued through mid-March. Then, suddenly, between 17 and 19 March, most of the rattlesnakes left their hibernation shelters, as if someone had given them the “all clear” signal. This was multiple rattlesnakes leaving multiple shelters at the same time – pretty amazing! By the way, you may also notice that I visited and recorded data more frequently in February last year. That’s because there were rattlesnakes to see and behavior to record (besides the science; it’s just more fun when there are rattlesnakes to see!).

If I combine the raw data from 2016 and 2017 for comparison, the chart gets pretty messy and trends are hard to make out. But we can create mathematical models for those same data that present a much clearer picture.

These are mathematical models derived from the data in the two charts above. Note the difference between the temperatures of the basking rattlesnakes in 2016, compared to 2017 where the snakes were still underground and their body temperatures were “chasing” the changing environmental temperature, first rising in late January, then leveling off as the weather started to cool, and finally declining as the weather turned cold again in late February.

You can see that mean February air temperatures started out much lower this year compared to 2016.  And, in 2016, with mean air temperatures exceeding 50F by early February and staying there, the rattlesnakes began to bask and their body temps took off as a result. This year, air temps started nearly ten degrees lower, rose briefly, but then took a nosedive in late February, keeping the rattlesnakes cool and underground so far.

Of course, some individuals do not behave in the same manner as most others. I have heard some reports of a few rattlesnakes being sighted in the past few weeks and one dog reportedly bitten already. While none of the telemetered rattlesnakes at Effie Yeaw have emerged from hibernation yet, one rattlesnake without a radio has been basking early – just as he has done each of the past two years. My old skinny Male 40 has been frequently laying in the sun at the entrance to his winter shelter for more than a week.

Male 40 basking in the late morning of 2 March 2017. Rattlesnakes, like other animals, have individual idiosyncrasies, and this animal has been the first to emerge and bask three years in a row. Interestingly, he is typically the last to leave the winter shelter and the first to return in the fall.

As you may recall, Male 40 was implanted with a transmitter in 2014 but I removed his second radio last spring and released him without one because he was not producing useful behavioral data. It was not that he was just behaving differently than the others (after all, unusual behavior is interesting and valuable to record), he has been chronically and significantly underweight, appears to be quite old, moves very little during the summer, and has never been found courting a female. Given his poor body condition, I was afraid that he would die during hibernation and his transmitter would not be retrievable. But, even without a radio, he continues to be sighted regularly and has now made it through another winter.

But most others seem to be waiting for some sustained warmer weather before venturing out.

Love is in the air

Rattlesnake love, that is!

I’ve been getting lots of questions after last night’s (17 April) KCRA News interview with a local “rattlesnake hunter” who makes his living keeping us all safe from rattlers. If you have been reading my blog, you know there is nothing new to be alarmed about. The last few hot days have not brought out the rattlesnakes. Indeed, general emergence from their winter dens occurred more than a month ago. Male rattlesnakes continue to be busy looking for and trying to mate with as many females as they can while the females hunt for mice, rats, and other prey. As sit-and-wait ambush predators, the females don’t move much and thus are seldom encountered by people. But the males have been and will continue to constantly search for females until late May or June, in the process turning up in yards and on trails and other places where they encounter people.

Once again, most bites can be avoided by watching where you put your unprotected hands and feet and leaving rattlesnakes alone when you encounter them.

We have been encountering numerous pairs of rattlesnakes in the Effie Yeaw Nature Preserve over the last few weeks. Here are brief video clips of a couple of examples: First, our telemetered Male 62 (blue/white paint in rattle), entwined with an unmarked female. These snakes were not moving during my brief visit but the males often accompany the females for many days but cannot keep courting them continuously (click here for video). You can see why in the video of Male 37 actively courting Female 41… it takes a lot of energy! (click here).

On 1 April, several hours after I videoed Male 37 courting Female 41, I returned and just missed a fight between two males over Female 41. As I approached, I briefly saw both males, with heads and necks high off the ground, twisted around one another. But one quickly fled, either from me or he had had enough of Male 37…who is a big healthy male rattlesnake! In any event, Male 37 was all excited and remained raised off the ground for a minute or more, guarding his girl (see photo below).

Male 37 still ready to fight shortly after another male retreated. Female 41 is coiled in the shade just below the male. I had videoed Male 37 courting Female 41 just a few hours before this scene.
Male 37 still ready to fight shortly after another male retreated. Female 41 is coiled in the shade just below the male. I had videoed Male 37 courting Female 41 at this spot just a few hours before this scene.

A video made a few years ago of two males fighting on the concrete in front of the Effie Yeaw Visitor Center doors is on the Nature Center website (or click here to see it).

 

General emergence appears to be underway (after a couple of false starts)

After a couple of false starts during warm periods in mid and late February, a new series of cool storms kept the Effie Yeaw Nature Center rattlesnakes immobile through the first half of March. On days with a little sunshine, both telemetered and other rattlesnakes were frequently found basking at the entrance to their shelters but they did not venture away from them. Natural selection tends to remove animals from the gene pool that wander too early and get caught in a late-season freeze. As if to demonstrate that it was cool temperature and not the rain that was keeping them inactive, several rattlesnakes were found lying out in the rain on days when the temperature was in the high 60s, despite the clouds.

Male 49 lying in the rain on 4 March 2016. Rattlesnakes are very adept at harvesting rain and dew, being very capable of sucking individual droplets off of vegetation or their own bodies. While that will drink from standing water when available, they don't seem to need such water sources and we have not detected tham traveling to either the ponds near the Nature Center or to the river.
Male 49 lying in the rain on 4 March 2016. Rattlesnakes are very adept at harvesting rain and dew, being able to suck individual droplets off of vegetation and their own bodies. While they will drink from standing water when available, they don’t seem to need such water sources and we have not detected them traveling to either the ponds near the Visitor Center or to the river. The only rattlesnakes discovered over the past two seasons around the Visitor Center (and its water sources) have been males during the breeding season – presumably looking for females, not water.

While the rattlesnakes continued to bask on sunny days, none of the telemetered animals moved between 29 February and 17 March. Then today, I discovered that 7 of the 9 telemetered rattlesnakes had left their shelters and moved significant distances in the past two days.CROR66 on 17 March 2016

I haven’t seen courtship yet. Female 41 and Male 49 hung out together for a month (16 February through 15 March) but they were only rarely touching one another and were usually coiled a couple of feet apart with no courtship observed. She is now hunting several dozen yards away and Male 49, without a transmitter, has disappeared.

The important message, however, is that rattlesnakes are on the move and encounters between people and rattlesnakes will increase immediately. Unfortunately, I have already seen photos of a rattlesnake bite from a few days ago in the foothills. Watching carefully where you put your hands and unprotected feet and leaving snakes alone when you encounter them would prevent almost all bites. If you must walk in vegetation or rocks where you cannot be sure what you’re stepping on, wear high-top shoes or boots that cover your feet and ankles. Of course, boots that cover some of your calf are better but most accidental snakebites (where the person is not intentionally interacting with the snake) are to the ankle and below.

Remember, you can’t save all the cute animals, eat all the tasty ones, kill all the ones that scare you, and have a functional ecosystem, too!

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!

Early emergence has begun!

As sunny 70+ degree days have been warming the ground recently, body temperatures of the telemetered rattlesnakes have been creeping up… but only from the 50-60F range into the higher 60s. Then, yesterday, I found Female 41 laying in the grass next to the log where she has spent the past two winters. But just being visible doesn’t constitute emergence.

I returned late this morning and found Female 39 visible for the first time, basking in dappled sun under the end of the log where she has spent the past two winters.

IMG_0091; 16 February 2016
This was all that was visible of Female 39 this morning but it takes only a small surface area in the sun to act as a radiator and warm the entire snake.

Then, not only did I find that Female 41 had moved about 20 feet from her winter shelter to a smaller nearby log, but I watched as Male 49, a large non-telemetered animal with white/green paint in his rattle, arrived at the same log and joined her. Although they coiled next to each other, I saw no actual courtship behavior during the 45 minutes I watched.

IMG_0117.CR2; 16 Feb 2016
Male 49, just a few feet from joining Female 41 this morning. Without a transmitter, I have no way of determining his body temperature or knowing where he spent the winter. An encounter with him is purely chance but white/green paint in his rattle makes him easily recognizable.

Body temperatures of Males 37 and 38, both of which spent the winter high on the bluff north of the preserve, were around 90F at midday today. Because their winter locations are almost inaccessible, I don’t know if they have actually left their hibernacula but they were both definitely in the sun today. Remember that ground temperature is much higher in the sun than the air temperature, particularly on south-facing slopes.

As of today, the other five telemetered rattlesnakes remain relatively cool and out of sight and the weather forecast looks like cloudy skies, cooler temps, and more rain over the next few days.

The study animals did not begin to leave their winter shelters until the end of the first week in March last year. Although this is three weeks earlier than last year, it is certainly a limited emergence with many snakes remaining underground and inactive. But the fact remains that some rattlesnakes have left their winter shelters, so “rattlesnake season” is definitely underway.

Remember that being careful where you place your unprotected hands and feet and leaving snakes alone when you find them would prevent almost all rattlesnake bites!

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.