My life has been crazy busy: finishing up the field season, travelling to Vancouver, and moving to San Diego from Davis. Now that I am finally settling down, I found the time to travel to BORR last weekend to check on the snakes and collect venom (we are collaborating with the Gibbs lab to examine individual and seasonal variation in venom composition). However, after two days of searching, we found ZERO snakes. Zip, nada, nothing! It's not like we were looking for snakes randomly. I have 20 of them with implanted radio-transmitters--this means I can track their exact location. However, after hours of tracking and re-tracking and re-tracking, NONE were on the surface. What the *bleep* are they doing?!
Northern Pacific Rattlesnakes mate bimodally. This means that they have two mating seasons: the spring and the fall. I was hoping to see mating activity last weekend, but instead I saw nothing. However, I did track several females to the exact same burrow as males. I found many male-female pairings and I found one two male-one female cluster. Although I could not see the snakes, I suspect they could be mating in shelter.
I also noticed that most of my snakes were hidden within rocky outcrops. This is strange for my site because there are very few of these. In the summer, snakes mainly hide in abundant squirrel burrows, but I did find that they tended to overwinter in the outcrops. This makes me wonder if they are moving to their overwintering sites early. Normally overwintering ("hibernation") begins in November and lasts through March. Check out the nice outcrops the snakes were in:
One snake in here:
One male and one female shacked up here:
TWO males, one female here:
The weekend wasn't a total loss though. We saw a nice little spider crossing the road and found that one of our females gave birth:
Tarantula!
A little baby outside its den:
Who knows what the snakes were up to? Maybe it was just too hot of a weekend. So much for me collecting venom...
After seven weeks of grueling field work, we have completed this year's data collection on squirrel-snake interactions. This year was much different than last year--the lack of rain led to less overall vegetation cover and what appeared to be reduced snake activity. Last year we recorded several strikes on squirrel pups, but we only saw a few this year. In fact, by the time we left BORR, most of the snakes had lost body mass instead of gaining it, suggesting that they still had not successfully found a meal. Eating seems like such a simple task to us, but for snakes, capturing prey is harder than it looks. It may take weeks before a snake is able to eat--snakes must complete three steps to successfully consume a meal: (1) strike and hit the prey, (2) envenomate the prey, and (3) relocate the prey after envenomation.
Our video recordings have shown that snakes can falter at all three steps. We have seen many instances where a snake clearly strikes and hits a prey item, and yet it never searches for it. We suspect that the snake was unable to successfully envenomate the prey, so it was not worth its time to go look for it. We have also seen snakes strike and kill prey, but unable to find the prey afterward. This year we found a squirrel pup that had been envenomated; still alive, but clearly succumbing to the venom. Upon our arrival, the pup ran into the burrow where the snake that struck it was. The snake emerged an hour later looking for the pup. It moved in and out of a triangle of three burrows (NOT the burrow that the pup was actually in) for a total of 5 hours searching for the dead pup. It never found it. It is so interesting that a snake could wait for days just to strike a squirrel and yet, even when it does, it may not relocate it afterward.
Teetee, male northern Pacific rattlesnake, in ambush right outside a squirrel burrow. It took him 13 days to get a meal.
Although it is tough being a foraging snake, feeding events still occur. Our most exciting feeding event this year was accomplished by Greeata, a female northern Pacific rattlesnake. It only took Greeata 2 days to successfully consume a squirrel pup. Initially, she chose several ambush sites outside of pup burrows at the base of a tree. However, in the end, she managed to strike a pup while underground beneath a log. While radio-tracking her, we found a dead squirrel pup just outside her burrow. We set up a camera on it, and lo and behold two hours later she emerged to consume it. It was quite an exciting day. Below I have posted a video of her selecting her ambush sites, and some pics of her consuming her big meal. Enjoy!
Greeata pulling the dead pup into the shade of her log
She swallows the pup at the entrance of her log burrow
Sorry for the delay in posting...I can't believe we are already in our third week of the field season! This year has been a blast so far. I have seven awesome undergraduate interns who are dedicated and hard-working-- working 12 hours a day, 6 days a week; tracking snakes, trapping squirrels, filming interactions, and running behavioral experiments (whew!). Our lab is able to capture rarely seen rattlesnake behaviors because we put in crazy amounts of effort, something I think few researchers are willing or unable to do. Our hard work often leads to rewarding surprises when we catch glimpses of animal interactions or behaviors that are rarely seen (and sometimes NEVER seen before). The fact that we see behaviors that have never been described highlights the importance of observational and basic ecological studies. Most researchers believe that the best science comes from empirically testing hypotheses by manipulating variables--but if we still don't understand how an organism interacts with its environment and other animals, how can we form hypotheses about it? I find it unfortunate that observational studies are not as valued as empirical studies; just my two cents.
Anyway, I have posted some pics of the new Crotalus Crew hard at work, and some of the rewarding things we have seen in the field. Enjoy!
Trevor and Rey stake out next to a squirrel colony (I hope they capture awesome interactions!)
Erynn, using radio-telemetry to track one of our snakes:
Tara, checking the body temps of our study snakes:
Mark, taking a pic of the king snake he found:
Me, implanting a snake with a radio-transmitter:
We found out that two-year-old rattlers can eat squirrel pups. Check out that bulge!
A male Bullock's Oriole hovering to the left of its nest:
Our most rewarding surprise yet! Two California king snakes mating on the dirt road:
Spring is in the air. Spring is a special time for snake enthusiasts because it marks the start of the rattlesnake active season. Rattlesnakes spend the winter in "hibernation" where they den in burrows or rocky outcrops. Some species of rattlesnake (for instance, Timber Rattlesnakes) overwinter in large communal dens with dozens of individuals sharing the same space. It was recently discovered that den-mates are often kin, and that rattlesnakes may preferentially den with their relatives. The species I study, the Northern Pacific Rattlesnake, is not known to den communally although we did see at least 6 snakes over-winter in the same rocky outcrop this year.
Spring also marks the time when neonate rattlesnakes become young-of-the-years. Female rattlesnakes give birth (yes, livebirth) during the fall before they retreat to their winter dens. The babies they produce are called neonates and in order to survive the winter, the neonates must find a meal or they will starve to death. Neonates, which are about the size of a pencil, are too small to consume squirrels, but they will eat insects and lizards. After the neonates eat, they will over-winter together at the site where they were born. These babies then emerge in spring and disperse from their natal homes. During the first year of their lives, baby rattlesnakes are called "young-of-the-years." Their rattles will consist of one natal button at the very tip and a couple of segments below to signify their shedding events. Once these individuals reach two-years of age, they will be called juveniles.
I have been traversing the hills of BORR to capture adult snakes for our upcoming field season (we start next Wednesday!), and I can't help but notice the freshness of spring. Babies are out and about. This little guy (or gal?) we found coiled in the grass next to a large rock. Perhaps, this was its overwintering site?
..and it's not just rattlesnakes that are producing babies. Last week I found a nest with a baby Red-tailed Hawk. Hopefully, the mother refrains from eating any of our study snakes!
In October I found a burrow where neonates had recently been born. I check in on the babies every time I visit the field site. I saw a total of four neonates in the fall (but the mother could have given birth to more), but only one remained when I returned this spring. Either the others were hiding in the burrow or they did not make it through the winter. By now, that one neonate has dispersed...I hope it is doing well.
Here is a video of the neonates moving about their burrow after I first found them in October. The video shows how small the neonates are compared to adult rattlesnakes (the burrow is about the size of a tennis ball and the neonates are about the size of a pencil). Although the video is long, if you are patient you will see that one neonate spends more than 10 minutes exploring the area around its home burrow (it emerges at 1:05 on the video, and the video is sped up to 3-4x for the sake of time). It flicks its tongue in and out as it moves about, presumably picking up chemical cues from its environment. Will it use these cues later in life to navigate back to this burrow next winter?
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