Rattlesnakes without the rattle?

My crappy cell phone photo of Crotolus molossus in the Rincon Mountains a few weeks ago.
My crappy cell phone photo of Crotolus molossus in the Rincon Mountains a few weeks ago.

I dream relatively often of being bit by a snake. Probably because 3-5 days a week, I am tromping off trail through Saguaro National Park to my research sites, and I try to stay hyper alert to the threat of venomous booby traps. I have been buzzed off my intended path by rattlesnakes several times a summer, both last year and this year. A few encounters, however, have involved a snake lying stretched out on a road or wash that peacefully watched me approach, notice it, and move around. Then there was the one my boyfriend stepped on as he jumped down a pile of volcanic rocks in the dark, which rattled angrily after the encounter, but was fortunately too busy falling off the opposite side of the rock as him to strike.

Have you heard the rumor that rattlesnakes are less and less likely to rattle? The hypothesis goes that because humans (or in some versions, human introduced livestock) are likely to kill rattlesnakes they discover, those that avoid rattling have a survival advantage. Whether the decreased propensity to rattle is a genetic defect in the tail muscles or a behavioral predisposition to silence, selection favoring that morph is increasing its frequency.

I had asked herpetologists at the Arizona-Sonora Desert Museum last summer about this hypothesis, and been told there was little or no evidence for it. I received a similar answer from herpetology students at University of Arizona.

So imagine my surprise to hear NPR feature herpetologists discussing anecdotal evidence (personal observations in an unstructured setup) supporting this hypothesis in South Dakota this week. A quick search on Google Scholar and Web of Science turned up no papers by them or anyone else providing solid evidence of such a trend. A broader web search only yielded a site categorizing that as a disputed urban legend.

When you think about this, it is a difficult hypothesis to test. Quantifying the strength of selection for rattling ability and behavior across a landscape would be difficult, at best. A herpetologist could perhaps find as many rattlesnakes as possible, and quantify the proportion inclined to rattle. But beyond the question of whether they could conduct a search that is unbiased by rattling propensity (which would make those snakes easier to detect), we have no reliable long term datasets against which to compare this metric to tell if the proportion of rattling rattlers has changed over time. A massive survey of land managers regarding the number of snakes they kill every year, and how those snakes were found, could provide a metric of risk to the snakes in those areas related to rattling. But quantifying the presumed benefits of rattling with regard to the rest of the world besides humans would be an important metric to include in determining whether rattling has a net benefit or cost to survival, and that would be harder to measure.

Based on my small encounter rate, last summer, only 1 of 4 snakes rattled at me. This summer, however, 4 of the 6 snakes encountered have sounded a warning (excluding the one my boyfriend stepped on, which  I’m not sure whether or not to count or not). So in my limited experience, snakes are rattling MORE frequently.

Herpetologists, do you know anyone who is testing this? Or have better ideas of how to test it? Also, feel free to tell me why it is not even a useful question for moving the field forward, and not particularly worthwhile to investigate.

Tortoise attack

The victor standing over his vanquished foe.
The victor standing over his vanquished foe (Gopherus agassizii). Apologies for poor cell phone camera quality of the photo.

I was walking down a wash in Chaos Canyon, west of Tucson, this morning, when I came across two tortoises evidently in the throes of a pitched battle.

One was already on his back. (That means he was losing.) He waved his legs, and struggled to roll. His breathing was audible and labored, liquid oozed from his backside, and occasionally squelchy farting sounds did as well. Losing precious moisture through urination even can be damning to these slow-metabolizing and slow-moving desert dwellers. I mentioned they were in a wash, but it has only rained twice there all summer (I have a rain gauge up the canyon). Being on one’s back for any length of time when you generally rely on gravity pulling your lungs open away from your shell is also a problem.

The other tortoise loomed over him, regularly bobbing his head aggressively, biting the downed animal’s feet, and lying on him to hold him down whenever he gained any momentum to rock back up.

I wondered if I should intervene. I don’t like to see animals suffering, and obviously the guy on his back was in a bad way, breathing and hydration wise. But this was an ongoing conflict the other tortoise seemed determined to end. (A very slow conflict, mind you. It was like watching baseball.) For all I knew, the guy on the ground deserved it. So I walked away with only video, leaving the tortoises to duke it out.

Further apologies for quality of crappy cell phone camera quality of the encounter. I recommend turning up the volume.

If you would like to to learn more about Gopherus agassizii, check out the Desert Museum or ask Taylor Edwards.

Mouse attack

I’m analyzing videos of mice eating. It’s often as boring as it sounds, leading my office mates to give me weird looks as I giggle madly, because I’m listening to Dane Cook or Read It and Weep while I go through hours of footage from infrared game cameras placed in the foothills, trained on small trays of seeds (sterilized millet, thanks for asking).

There are a lot of videos of wind blowing the grass around. Some of foxes (see last post).

A lot of videos provide useful data, but are kind of crappy images like this one:

Then, out of the blue, I spy something unusual, and sit up straight in my chair. Mid-giggle. I take  my feet off my desk. I know I can’t tell these sly little pocket mice apart, because they lack distinguishing markings.

(By the way, my research group spent substantial time and effort earlier this summer trying to build a bait station that dotted mice with sharpie or hair dye or something when they ate the seeds. We wanted a herd of itty bitty jaguars to keep track of. Nothing has worked well yet. If you have any ideas, please let me know!!!!)

Back to the unusual bit. Because I can’t tell these mice apart, I can’t tell how many eat from my bait station over the course of a night. It could be one mouse that defends its territory. Or many with overlapping home ranges.

Here, in this unusual video, was a clue!

Another Chaetodipus spp. lurks in the background while the normally alert diner nibbles on delicious millet.

I write something dramatic in my spreadsheet, probably in all caps under the “Notes” column for this video. I write something along the lines of “OMG ANOTHER MOUSE LURKING.” It’s a technical scientific term, lurking.

I lean forward in my chair and click on the next video.

Nothing. It’s just wind in the grass. I’m not going to waste your ten seconds with that video, not when mine are already spent.

But I keep watching. And seven minutes later (in 10 second increments every few minutes, mind you)……


Detours, including gila monsters

My academic adviser reminded me of something today that I have frequently noticed. A side project or half-baked pilot project can really take over and become a successful program.

In that spirit, although I have rarely had the energy to post on this blog with my field season in full swing, 4:30am mornings and all, I have taken some neat detours this summer. I’ll share a few side sightings here.

Although my daily hike is usually in search of seedlings, I manage to see owls and foxes, deer and tortoises. Sometimes these encounters are painful, like the bite from a Pogonomyrmex (harvester) ant that made my whole body flush red and hot for an hour (and scared the heck out of me, miles from the car or nearest medical treatment) or the bees that have twice climbed into my shirt to sting my stomach as I try to extricate them. Others were more gratifying, such as watching a beautifully tri-colored four foot snake cruising around near my feet, posting a photo to Facebook on the spot, and having an ID within minutes. (Thanks, Shea!)

Just this morning, my fellow field adventurers and I saw a gila monster and a rattlesnake within about ten minutes of each other in the Rincon Mountains. Just a few days ago I started analyzing our video study from the Tucson Mountains, and came across some fox footage. Enjoy!

Update Aug. 21: Here’s that fox video that was missing yesterday due to technical difficulties:

I set off this rattlesnake when I walked too close to the shrub.
This Sonoran whip snake (Masticophis bislineatus) was just snaking around near us.
Gila monster!