Category: Winter 2015/16

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!

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