Bandshell

Halfway between Tucson and Phoenix, a crumbling granite hillside gives way to a cactus-studded alluvial plain. Small, sandy washes break up this landscape and facilitate the growth of desert trees. Here, the western diamondbacked rattlesnake flourishes during times of plenty and, in leaner times, retreats to refuges to idle until conditions improve.

In February of 2010 we discovered a number of rocky refuges used by western diamondbacks to spend the winter. These sites are treasured by generations of snakes for the protection offered from freezing temperatures, an arrangement of safe basking locations, and, perhaps, a rock surface that funnels a sprinkle of rain into a drinkable collection.

In mid-February of 2011, we visited to this area again to find that snakes had returned to most of these sites. One spot, in particular, intrigued us. Whereas last year it was found to house but one snake, it now contained several, perhaps even five snakes. We call it Bandshell, and it’s a small eruption of rock from the hillside with a deep, nearly vertical crevice into an inverted rock face.

We mounted a timelapse camera near the face of Bandshell in hopes that we would see how many snakes used this den this winter and perhaps get a glimpse of some emergence (‘egress’) behavior. We were more successful than we could’ve imagined.

25 February – 2 March 2011

With the exception of a weak storm front moving through on the 27^th, the cameras record only a lack of activity by the snakes.

3 March 2011

Two young males, Scarecrow (S) and the Tin Woodsman (T) make their film debut.

These snakes engaged in combat, a ritualistic wrestling match whose outcome depends on which snake is better able to hold its opponent to the ground while intertwining. The victor may then be left to court a contested female.

Later that day, we return to swap data cards in the camera. About 5 m downslope of the den, we find T, stretched out amid brush and rocks. We are careful not to disturb him.

T enters the den at 1630, and S follows a quarter hour behind.

4 March 2011

A near repeat of yesterday. S slides out first with T following close behind.

This time, however, S appears reluctant to engage in combat.

T returns to the den at 12:48.

(Because of higher temporal resolution, the camera shuts off at 13:20 on 4 March)

6 March 2011

We arrive at 1000 and exchange memory cards. No snakes are evident outside the den.

T emerges and hangs around den.

S enters the den later that afternoon.

7 March 2011

Only T is active.

8 March 2011

T emerges, returns to the den, reemerges.

9 March 2011

No snake activity recorded.

10 March 2011

The warmest day so far this year brings some fresh characters.

The Cowardly Lion (C), a much larger male, emerges.

A female, Dorothy (D), emerges and coils at the entrance of the den.

T emerges and courts D. If you look carefully, courtship appears to continue just out of the frame in the upper left. At 1318, S emerges from the den, approaches the pair offscreen, and, apparently engages T in brief combat.

C crosses the frame.

T checks on the den.

C emerges from the den. S is not far behind.

T crosses the frame

A second female, Auntie Em (E), emerges.

We return to swap cards, but cannot do so without disturbing snakes around the den, so we postpone. E is still coiled at the entrance of the den.

S flanks the other side of the camera, about 2 m NE of the den entrance.

C returns to the frame to court E.

We return to find that S has vacated his post, and we take a chance on disturbing C and E, switching memory cards in the camera mostly hidden from their view. Although E is facing away, she appears to take a cue from C, who enters the den shortly after our departure.

About 20 m below the den, T sits in coil.

12 March 2011

The camera is now set to begin at 0800 rather than 0900, capturing the emergence of C.

E emerges and is soon joined by C.

At this point, the camera mysteriously shut off for 24 hours.

13 March 2011

E is visible coiled in the shade. C enters and courts her for 90 minutes, alternately chin rubbing and resting out of contact with her. Several times, as C rests, E moves her head slightly and appears to prompt him into another round of chin rubbing (e.g., at 14:58, 15:13, 15:28, 15:49).

14 March 2011

C is already out basking when the camera activates at 0800.

Later, T and one of the females emerge and interact. C returns, and the other snakes return to the den. C monitors then den, and at 09:53 E emerges, followed by T (10:05). E appears to be trying to re-enter the den as T vigorously courts her.

With E or T visible in the entrance to the den, C comes back and checks on the den several times., finally coiling in the shade to the left of the den entrance.

The next 90 minutes are obscured by the high contrast between areas in sun and shade, but at 12:24 the snakes are visible, with C out front, E (below) and T (above) in the den entrance.

15 March 2011

The only activity on this day is C posting up at the den entrance for a bit.

16 March 2011

Again, C is the only snake caught in the frame today as he checks on the den.

17 March 2011

A new snake, Oz (O) checks on the den. We think this snake overwintered at a different site.

18 March 2011

C checks on the den.

19 March 2011

Camera is taken down at 1000. Just a few meters downhill from the den, we discover E and C copulating.

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Alice

Memorial Day Weekend 2010. Alice is a big, beautiful, dark female Arizona black rattlesnake with mustard yellow scales outlining each dorsal blotch. We first encountered her ~20 meters from a known rattlesnake den. Several of our party walked right by before we discovered her, coiled at an opening beneath a boulder, without her rattling or stirring. This is actually pretty typical behavior for rattlesnakes. Their primary defense is to remain still, silent, and rely on camouflage.

Alice was healthy-looking, and we could tell by her distended posterior that she’d be expecting babies in a few months. She was marked with lavender paint on her rattle and we noted several pattern aberrancies (see below). For the next few days Alice remained quietly coiled by her boulder as we passed by to monitor other snakes.

The two basal (closest to the body) segments of the rattle are painted lavender - it is purposely difficult to see so that she is not too visible to potentials predators.

The neck blotch (dorsal blotch closest to the head) is one that varies much between snakes. Alice also has a relatively small blotch on her right and her left separated by one normal blotch (here pictured just below her head).

We returned on 27 July to find Alice coiled in nearly the same spot we left her two months prior. With the approach of birthing season (late August – early September), we repeated visits weekly, and Alice would reliably be found contently coiled in dappled sunlight. We respected her space, using binoculars and telephotography to verify her paint and markings, and she appeared unfazed by these activities. Despite our sporadic visits, it is unlikely that we missed a lot of Alice’s activity; pregnant rattlesnakes usually don’t feed or don’t make large movements.

A rattlesnake hunts by finding a promising spot to ambush prey, and then sits and waits with an ‘S’ curve in its neck, ready to spring when a lizard, bird or rodent happens across its strike zone. Critical to an ambush is unpredictability; a hunting rattlesnake might try several spots in a small area before moving off to a new hunting patch. We don’t know when Alice might have eaten last, or whether she would if a meal presented itself. But she was never seen in a hunting posture or with any evidence of recently ingested food item. So it is likely that Alice did not feed during her pregnancy, which is typical of most rattlesnakes.

Alice’s boulder complex has a footprint little bigger than a compact car. Despite its small size, we only observed her using a handful of spots during a couple of dozen observations, and she did so like clockwork. She would emerge in the morning at the mouth of a large opening, around 10am when the sun was angled above the pinetops. As the sun arced higher, she would retreat partially or completely into the deep shade of her boulder to keep from overheating. By afternoon, as the sun again filtered through trees to the west, Alice would emerge onto a west-facing rock ledge. Here she would stay until she had gained all the heat she could, and around 5pm she would retreat back under her boulder for the evening. On cool or cloudy days, she would be visible all day, ready to drink up any drops of rain that might collect on her or the granite walls of her home.

Alice’s home was a temple to the sun, and her daily ritual was an expression of her strong maternal instinct. Snakes are ectotherms; they depend on their environment to achieve and maintain a favorable body temperature. And maintaining a proper body temperature is especially important for a pregnant snake like Alice, whose babies’ development and timely delivery require as consistent warmth as mom can provide. Unfortunately, Alice lives in a cool, shady forest where staying warm is a challenge.

Despite apparently not feeding, Alice grew fatter and fatter over the next few weeks.

12 September 2010. Alice was coiled in her favorite spot at the opening beneath the boulder with seven neonate (newborn) rattlesnakes!

Rattlesnakes are viviparous: they give birth to live young instead of laying eggs (oviparous). Although venomous at birth, neonate rattlesnakes are not immediately on their own and are highly vulnerable to predators. At this stage, neonates seem rather helpless. A couple days after birth their eyes cloud up in preparation for shed, which impairs their vision. They do not appear to be wary of predators. Neonates fearlessly explore their environment until the adult female decides they have strayed too far from the safe spot she has chosen as the nursery and gently herds them back or takes on a strident posture to alert them to possible hazard.

Two weeks later, Alice was gone, not to return to her favorite spot again this year. One of her daughters was coiled a few meters away, in a hunting posture in leaf litter.

Indeed the lucky girl had already acquired her first meal, likely one of the many newly hatched lizards. A week or two before the rattlesnakes were born three different species of lizards (Greater short-horned lizard, Phrynosoma hernandesi; Plateau fence lizard, Sceloporus tristichus; Plateau striped whiptail, Aspidoscelis velox) hatched and this area was literally crawling with lizards. Could this abundance of food, perfectly sized for neonate rattlesnakes, be the reason Alice chose this place to have her family? Will this little girl return to birth her young here in a few years?

Are aggregations of Arizona black rattlesnakes stable and complex social groups?

In 2010, we initiated a study of social behavior in Arizona black rattlesnakes (Crotalus cerberus) at sites where they aggregate. Here is a preview of our videos.

Surveillance and timelapse videos taken at Arizona black rattlesnake hibernacula. Timelapse videos created with the PlantCam by Wingscapes and Adobe® After Effects® CS4 software.

This first short video was taken at a winter hibernaculum (den) shared by Arizona black rattlesnakes and striped whipsnakes (Coluber taeniatus). A rattlesnake quickly exits out of the dark opening on the left and a whipsnake is visible on the right.

This is another den shared by rattlesnakes and striped whipsnakes. At ~15s, a whipsnake appears to fly out of the left side of the crack; another whipsnake peeks out at the bottom right.

In the beginning of this video a male rattlesnake is coiled just outside the den entrance. A female slowly crawls out of the den to join him.

In this video a male rattlesnake is coiled outside the den during a light rain. He moves his head around to drink rain off his coils and the nearby rock before crawling inside.