Year end wrap-up

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

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

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

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

 

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

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

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

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

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

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

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

The study comes to an end

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

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

So stay tuned!

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

Interesting rattlesnake news

How well do rattlesnakes tolerate surgically-implanted transmitters?

As I have discussed before, there is a long (20+ years) history of telemetry studies of rattlesnakes in which individual animals tolerate the transmitters for years, enduring periodic surgeries to replace the radios. The animals thrive, repeatedly producing offspring and growing at the same rate as rattlesnakes without transmitters.

I bring this up because of a phone call last weekend from the landowner where I conducted my El Dorado County field study. He had just encountered the first Northern Pacific Rattlesnake I ever marked and telemetered, still identifiable by the yellow-over-yellow paint remaining in his rattle. He is now an exceptionally large male with twelve rattle segments – but in 2009, he was a young animal with a tapered unbroken rattle. He eventually endured four annual surgeries to implant and replace transmitters, followed by a fifth surgery in 2013 to remove his last radio.

Here is a PowerPoint slide of Male 01
Here is a PowerPoint slide I use to illustrate how marking the rattles helps to judge growth and shedding frequency. The photos are of my Male #1. It also demonstrates how the rattle breaks over time. According to my friend, the 2011 paint is now just two segments from being lost but the snake is big,  healthy, and thriving. You can see that, once the early tapered segments are gone, the rattle offers little insight into the age of the snake.

Male 01 being sighted alive and healthy is just more evidence that the surgical protocol and other study methods used by me and many of my rattlesnake-researcher colleagues is well tolerated by the animals we seek to learn more about.

Rattlesnake intelligence?

Despite my frequent admonition that we often tend to give rattlesnakes and similar animals too much credit for cognitive thought, friends at San Diego State University recently published some compelling evidence that rattlesnakes may learn from experience and apply those lessons to anticipate and mitigate problems during future similar circumstances. Bree Putman and Rulon Clark have spent years studying rattlesnake predation tactics by setting up video cameras on hunting rattlesnakes and recording their predatory encounters with small mammals. (This works because rattlesnakes are ambush hunters that sit still for long periods of time, waiting for prey to wander by.)

While reviewing 2000 hours of video, Bree and Rulon discovered two examples of rattlesnakes using their heads and necks to move foliage out of the way that might otherwise interfere with a strike when prey wanders close (click here for video). The animals involved were Northern Pacific Rattlesnakes – the same species as we have in the Sacramento area. Similar behavior has been reported a couple of times in the past, once involving a Prairie Rattlesnake (Crotalus viridis) and once involving an Arizona Blacktail Rattlesnake (Crotalus molossus); both these incidents were witnessed by observers but not recorded.

Thus, evidence continues to accumulate that rattlesnakes are likely more social and maybe more intelligent than previously thought – although many habits are undoubtedly genetically programmed by natural selection. The new report by Putman and Clark is contained in the current issue of The Southwestern Naturalist (volume 60, number 4; December 2015).

For more interesting videos of natural predatory behavior by rattlesnakes, go to Rulon’s YouTube page.

2015 Wrap-up

At the conclusion of my last post (29 October), I mentioned that it appeared that all of the rattlesnakes had settled into their winter shelters and, indeed, two days later, they had done so. Of the six telemetered rattlesnakes for which I have refuge locations from last winter, five of them returned to the same refuge this winter. The exception is Male 38, who spent last winter under a log in the flat floodplain but this winter is high on the hillside near the northern preserve boundary. On 31 October, I climbed the bluff and found Male 38’s location just a few meters away from Male 37, who had returned to his 2014/2015 location. Both animals’ radio signals were originating from under thick vegetation covered by wild grape vines high on the steep hillside. Both are undoubtedly underground, likely in ground squirrel burrows.

Of the eight telemetered rattlesnakes this winter, three are hibernating together in one refuge, two are together in another, and three are hibernating alone in different locations (including Males 37 and 38). Of course, there may be non-telemetered rattlesnakes with any or all of them but that’s hard to determine at this stage. I will do some burrow camera work soon but that is often inconclusive, as their shelters are often too deep or have too many sharp turns for the camera. Even if I reach them, I cannot visually identify the snakes without looking for paint in their rattles, which are usually covered by their coils. In warm weather I often poke them with the camera to get them to expose their rattles but I don’t want to disturb them when they are cold.

So how cold are they? The table below shows the ground surface temperature in sun and shade, as well as the coldest, warmest, and average body temperatures of the telemetered rattlesnakes over the last five weeks of 2015. I will continue to occasionally collect temperature data until spring emergence. That will be foretold by the snakes beginning to bask in the morning sun, probably sometime in March. Even if I don’t catch them basking, they won’t be able to hide their elevated body temperatures; then we’ll know they’re about to begin their 2016 season.

Brumation temp tbl 2015
Brumation vs. hibernation

Several people have asked me about the term “brumation” and the difference between brumation and hibernation. According to Harvey Lillywhite’s Dictionary of Herpetology (2008, Krieger Publishing, Malabar, FL), brumation is:

“A condition of torpor during extended periods of low temperature (winter dormancy), intended to distinguish such states of inactivity of amphibians and reptiles from the term ‘hibernation’ that is used commonly in reference to birds and mammals. Term coined by W. Mayhew (Comp. Biochem. Physiol. 16:103–119, 1965)”

When used regarding endotherms (animals that regulate their body temperature internally, like birds and mammals), “hibernation” generally describes a state of deep sleep in which an animal lowers its body temperature and metabolism to conserve stored nutrients during harsh winters, such as many bears and bats. In reality, ectotherms like rattlesnakes do essentially the same thing with two exceptions: they remain responsive and do not “sleep” although they become very sluggish as they get cold and, after all, it is not a big physiological change for ectotherms because their body temperature varies with the environment year-round. As a result, many herpetologists ignore brumation and use hibernation to describe winter inactivity in reptiles and amphibians, too (e.g., F. Harvey Pough, et al. 2016. Herpetology, 4th ed., Sinauer Associates, Sunderland, MA).

Best wishes for a safe and Happy New Year!

Mike

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.

24 February 2015

Little has changed over the past ten days; fence lizards basking midday when it’s sunny but no rattlesnakes out when I have checked. The only interesting development was on 19 February, when I found that Female 41 had moved again, this time about 7 m (23 ft) to another smaller log where she was out of sight.

Today, I started collecting data on my Droid smartphone, rather than taking paper notes. Using a program called iFormBuilder, I have been able to create a menu that allows me to record twenty-nine observations of things like where a snake is, what it’s doing, temperatures, other environmental data, nearby flora, etc., mostly by making choices on drop-down menus. When I’m done, it automatically up-links to my computer at home where the data is waiting to be saved in an Excel spreadsheet. This not only helps standardize the data I collect but it saves an unbelievable amount of time by eliminating the need to manually enter data from paper notes. I used a similar system during my 40-month field study of Mohave rattlesnakes (2001-2004) and recorded something like 150,000 data points during more than 3700 encounters with the snakes; if that had been done on paper, I would still be working on data entry!

At 12:17 PM, I found a small unmarked male rattlesnake laying in the sun at the same refuge shared by CRORs 35, 38, 39, 40 and several others. He was captured (CROR45) and processed. At 242 grams (9 oz), he is large enough for a transmitter (the rule is the transmitter should not exceed 5% of the snake’s body mass, so my 9 g transmitters require a snake of 180 g (6 oz) or larger), however, releasing him with a fresh surgery when the weather is likely to be cold for weeks to come is not good. Physiological processes in ectotherms (animals that rely on the environment for body heat rather than making their own) slow way down when they get cool, which includes their immune systems and their ability to heal wounds. So Male #45 will be processed (measured, marked, etc.) and released where he was captured without a transmitter.

Before releasing him, however, I wanted to see if he was the same snake I saw on 14 February, since his body size and rattle looked very similar. But after comparing a photo of his face with my photo of the unidentified snake from 14 Feb, I found that they are not the same animal. In the photos below, note the difference in shape of the margin of the postnasal scale at (1), the speckling pattern of the preocular scale at (2), and the shape just under the eye of the margin of the dark postocular stripe at (3). Of course, there are many other dissimilarities in the photos… bottom line, it’s not the same animal.Compare 45 with UNID

The last development to report from 24 February is that I could not get a radio signal from Male #40. Thinking that he might have left the refuge with all the warm sunny days, I walked around for awhile without detecting his signal, so I returned to the refuge and used the burrow camera to look forCROR40 24Feb15 him. Sure enough, there he was (yellow/blue paint in his rattle). This is the third transmitter to fail prematurely and all are from the same batch of refurbished units (they last a year and, after removal from the snake, are returned to the manufacturer to be rebuilt with new batteries). As I have mentioned previously, the manufacturer very rarely gets a bad lot of batteries which then affects an entire series of their transmitters. The good news is that I have no more of that batch of transmitters. The bad news: CRORs 35, 38, and 39 all have those transmitters in them. Transmitters have already failed in 36, 37, and now 40. Hopefully, I can catch Male #40 basking and catch him before he leaves the refuge – which could be any time, given the unseasonably warm days. I am reminded that one of those transmitters functioned for over a year in the last telemetered rattlesnake at my El Dorado Hills study site, so maybe all of them don’t contain bad batteries. Nonetheless, I will replace the transmitters in 35, 38, and 39 as soon as they leave their winter refuge, rather than waiting for their normal 12-month replacement.