Monday, December 9, 2013

Snakes and the Ecology of Fear

Fear is a common word and feeling associated with snakes. Ophidiophobia is one of the most shared fears of people worldwide. Although this post will not discuss the many proposed hypotheses for people’s fear of snakes, it will cover how fear can influence ecosystem processes. This post will mainly focus on rattlesnakes as predators – all statistics/facts I report are based on studies of North American rattlesnake populations.

Most people are afraid of snakes because of their nasty reputation which is propagated by the popular media. Snakes are deemed aggressive killers, and although many studies have demonstrated the docility of snake temperament, they are in fact killers. However, snakes are not killers of humans (less than 0.001% of all snake bites in the U.S. result in death), but killers of their small mammal prey. This makes our fear of snakes irrational, but small mammals have much to fear. This fear dictates how small mammals live their lives, often impacting whole ecosystems.

When predators chase and kill their prey they exert consumptive effects on the prey population

When people think of predators, they usually think of a predator chasing down and eating its prey. Direct killing events are important in maintaining prey population numbers, but a predator’s consumptive effects (those due to the direct killing and consumption of prey) on the ecosystem are usually nothing compared to its non-consumptive effects (those that do not result in the direct death of prey). For instance, a lioness can chase and take down one wildebeest, but the stampede of the wildebeest herd created by this chase may kill other wildebeest and other species (remember the Lion King stampede?), destroy vegetation, and induce a stress response in all animals involved that will persist long after the initial predation event.  

Involvement in a life-threatening predatory attack has been shown to enable rapid and enduring learning in prey species, to induce physiological stress significant enough to impair the day-to-day activities of prey, and to drastically affect the functioning of food chains in the ecosystem. Such non-consumptive predatory effects are collectively called the Ecology of Fear. Here, I will discuss how the stress responses of prey to their predators affect many aspects of their lives, and how rattlesnakes can be used as model predators to study stress in wild small mammal populations. 

First, let’s define what a stressor is. A stressor is any stimulus that either directly threatens an animal’s survival or is perceived to do so. Fear-induced stress is psychological and occurs when a stimulus is perceived by an animal as threatening through evaluation by the cognitive regions of the brain. Cues that indicate predator presence can invoke fear-induced stress.

The stress response pathway starts in the brain at the hypothalamus which releases CRH (corticotropin-releasing hormone) into the pituitary. This stimulates the pituitary to release ACTH (adrenocorticotropic hormone) into the blood stream. ACTH stimulates the adrenal glands to produce stress hormones (corticosteroids). Corticosteroids create the physiological responses we feel to stress and influence our behaviors. The is normally called the HPA-axis. 

We also must keep in mind that not all stress is bad. In fact, the stress response pathway evolved to help animals cope with fluctuations in their environment. Most people believe that stress starts to have negative health effects only when it persists for too long. However, whether prolonged exposure to predators causes long-term negative impacts on prey populations is still debatable. It is proposed that although the stress response of prey to predators alters the prey’s immediate health, the long-term response is adaptive.   

When exposed to predators, prey alter their day-to-day activities. For example, they may forgo feeding in food patches where they usually consume high energy food, and instead feed in low energy food patches. Predator presence not only limits where prey can feed, but can also cause fear-induced stress that increases prey metabolic rate (breathing rate) which accelerates the rate at which prey use energy. So prey burn a lot of energy, but cannot access the food to replace this lost energy because they are afraid of predators. If this cycle persists long enough, prey body condition can drastically decrease and could result in death by starvation.   

Prey may also forgo mating or have lower reproductive success when predators are perceived to be present. Several studies have shown that females of different species of animals exhibit lower birth rates or litter sizes when in a state of fear-induced stress. Forgoing mating is considered adaptive if it is better for prey to wait to have babies after the amount of predators in the area has declined. This is called predator-induced breeding suppression.

Older yellow-belled marmot mothers that exhibit high levels of stress hormones produce significantly smaller litters than mothers with low levels of stress hormones (as seen by the graph). Taken from Monclus et al. (2011).

I have just mentioned only two of a myriad of ways that predators affect prey other than direct consumption. The non-lethal effects of predators make up a major field of research right now, and studies on these effects have been influential in understanding stress-related diseases in humans, like PTSD (post traumatic stress disorder). However, there are several problems with many of these predator-prey studies. First, most studies are conducted in a controlled laboratory environment and as several papers have pointed out, results found in the lab don’t always translate well to wild animal populations. Second, the few studies on wild animal populations that do exist do not actually know the exact locations of their predators, or how predators behave in response to their prey. An index of predator density is usually estimated through monitoring surveys (traps and wildlife cameras), and this index is correlated to the stress levels of wild prey populations. Wild prey responses to actual predators are almost never examined. Studies that use rattlesnakes as model predators may provide answers on whether prey exhibit fear-induced stress when actively confronting a real predator.   

Why are rattlesnakes model predators for predator-prey studies? Let me tell you.
  1. These snakes are large-bodied and amenable to implantation of radio transmitters. Radio transmitters emit a radio wave that can be picked up by a receiver, allowing researchers to track the exact location of individual snakes. Thus, we can know where snakes implanted with transmitters are at all times.
  2. Rattlesnakes are sit-and-wait ambush hunters that remain at a hunting site for hours to days waiting for unsuspecting prey to pass them by. This is great because once we know where a snake is, we know it’s going to be there for a while. We can monitor a snake’s location and see how prey respond to it. Since rattlesnakes have low endurance and do not chase their prey, their prey are also more willing to inspect them.
  3. Rattlesnakes are not easily disturbed by human observers, usually relying on camouflage to blend into their surroundings. Thus, researchers including myself have figured out that one can easily set up fixed video cameras overlooking snakes to record when they interact with prey.
  4. Researchers can easily restrain rattlesnakes in the field when they want to present a live predator to specific individuals of wild prey. Most studies are only able to use predator cues such a scent, or models/replicas of predators to elicit prey responses.


Photos of the typical ambush posture of hunting rattlesnakes (which consists of a tightly coiled body), and the wireless network security cameras we use to record natural rattlesnake behaviors.

Because of the abovementioned qualities of rattlesnakes, we can use them to more easily study fear-induced stress in wild prey. For instance, we can present a restrained rattlesnake to focal prey individuals, and examine how long each individual's stress response persists after discovering the snake. If prey experience prolonged stress after encountering a snake, they may reduce time spent on other important activities such as feeding or mating, as mentioned previously. This could have ecosystem level consequences. For example, ground squirrels create burrow systems that are widely used by many different animals in their ecosystem. If squirrels are greatly concerned with avoiding snake predators, they may reduce time spent on burrow construction, limiting the amount of available burrows to others in the area. We are currently conducting these types of studies on wild ground squirrel populations in California. 

As in previous studies, we can examine how the density of rattlesnakes in an area affects their prey’s stress response. Most studies have examined how mammalian or avian predators affect prey populations. An important distinction between these two predators and rattlesnakes is that rattlesnakes are ectothermic, or ‘cold-blooded’, while mammals and birds are endothermic, or ‘warm-blooded’. Cold-blooded animals are often found at much higher densities in an ecosystem than warm-blooded animals. Because rattlesnakes occur at higher densities than large mammalian carnivores, their effects on shared prey are likely different. For instance, theory suggests that prey should not mount strong defensive responses to predators when they encounter predators too often. Thus, prey may not respond to rattlesnake populations as strongly as mammalian carnivore populations. 

Finally, rattlesnakes also exhibit distinct activity seasons as a consequence of being ‘cold-blooded’. When the climate becomes either too hot or too cold they ‘hunker down’ in a refuge, patiently waiting for the bad weather to pass. Their prey may acknowledge times when snakes are inactive and exhibit changes in their activities and stress response pathway. For instance, prey may take advantage of cold days (when snakes are incapable of a lot of activity) by feeding/mating more. An increase in prey behaviors may be correlated with changes in stress hormone levels.      

The Ecology of Fear is an exciting field of research from which we can not only learn a lot about wild animal responses to predators, but also our own responses to traumatic events. Few studies have examined the fear-induced effects of snake predation even though rattlesnakes are model predators for such studies. I hope that my research along with research from others will advance our knowledge on this topic. 

This post was inspired by a special feature on the ecology of stress in the journal, Functional Ecology, published this year. I took several of my examples from two particular papers in this special feature and am grateful for these authors' review of the literature:

Other resources used in this post:

This post is also a part of the first herpetology blog carnival organized by a network of students, naturalists, and professionals whose goal is to use social media to communicate information about amphibian and reptile natural history, science, and conservation. Our inaugural event is inspired by the Year of the Snake, and so we are writing blog posts about the diversity of ecosystem services provided by snakes. We encourage everyone to follow us on Twitter using #SnakesAtYourService. We hope this social media event will be the first of many that touch on different themes related to the importance of amphibians and reptiles.

'Snakes At Your Service'  participating blogs and authors:

Monday, December 2, 2013

#SnakesAtYourService Blogging Carnival - 9th December!

In one week, a social media network that I am a part of will launch a blog carnival to advance amphibian and reptile outreach and conservation. Social media has recently emerged as an important tool in conducting effective science education and outreach. A group of animals that has much to gain from this outreach include the amphibians and reptiles. Many reptiles and amphibians occur in large numbers in the ecosystems they inhabit, are top predators, and provide important services to their habitats. However, these animals are often cryptic, and the general public seems to overlook their presence and great importance. As a result, we have decided to bring attention to a network of students, naturalists, and professionals that use social media to communicate information about amphibian and reptile natural history, science, and conservation.

Our inaugural event is inspired by Partner in Amphibian and Reptile Conservation’s (PARC) Year of the Snake. On December 9th we will be publishing blog posts about the diversity of ecosystem services provided by snakes. Snakes are generally vilified in the popular media. Our goal is to create new media that accurately portrays snakes’ importance in the hopes of decreasing the negative perception many people hold against them. Leading up to this day, we will be tweeting about snake ecosystem services using the hashtag #SnakesatyourService. We encourage everyone to follow us on Twitter, visit our blogs on December 9th and help spread the word about our outreach event. We hope this to be the first of many social media events portraying different themes related to the importance of amphibians and reptiles.


December 9th 2013 Participating Blogs and Authors:

Life is Short But Snakes are Long: Ecology of Snake Sheds by Andrew Durso @am_durso

Living Alongside Wildlife: Kingsnakes Keep Copperheads in Check by David Steen @AlongsideWild

Nature Afield: Pythons as Model Organisms by Heidi Smith @HeidiKayDeidl

Ophidiophilia: Converting Ophidiophobes to Ophidiophiles, One Kid at a Time by Emily Taylor @snakeymama

The Traveling Taxonomist: Snakes of Madagascar: Cultural and Ecological Roles by Mark Scherz @MarkScherz

Social Snakes: Good Neighbors Make a Greater Impact: How Viper Behavior Increases Their Effect on Prey Populations by Melissa Amarello @SocialSnakes

Strike, Rattle, and Roll: Snakes and the Ecology of Fear by Bree Putman @breeput

Australian Museum: When the Frogs Go, the Snakes Follow by Jodi Rowley @jodirowley


Contact Information: David Steen, Ph.D. (

Tuesday, November 12, 2013

Snakes Are Clumsy, Just Like Us!

Like all animals, snakes are not perfect. They make mistakes and sometimes misjudge their abilities. Even though you would assume snakes would be clumsy all the time because they are limbless, they normally are quite graceful. They have extremely well-developed musculature and scales that allow them to move in various ways. In fact, they can do almost anything a four-limbed animal can do, using only their tube-shaped body. 

For instance, they can climb trees

 hold their food in place while eating,

and even soar through the air.

However, every once in a while, they mess up. After many years of watching snakes in the wild, I've seen some pretty funny snake mistakes. Here are a few of my stories from the field:

1) If you've ever hiked the California foothills in late summer, you may have accidentally fallen down a steep hill from trying to walk on extremely slippery dried out grass. Well, I've also seen a snake make this same mistake - accidentally sliding all the way down a dry grassy hill it was trying to traverse. Poor little girl was dazed and confused after her clumsy fall.

2) Snakes eat pretty big meals which sometimes make it hard for them to move. This past summer we recorded a snake trying to relocate sites after having consumed an adult ground squirrel. This squirrel was roughly half the total body mass of the snake - that's one BIG meal. After consuming the squirrel, the snake attempted to exit a log, but got stuck in the exit hole by his huge food bulge. After a couple seconds of trying to squeeze through, he finally realized that he needed a new exit strategy. Check out the video of his snake mistake below!

3) A couple years back, we captured footage of a snake making a huge mistake while attempting to strike a ground squirrel pup. This snake lunged forward during the attack, but missed the pup, and instead fell down a hill. Needless to say, we felt bad for the poor guy. He lost a tasty meal and got injured in the process. Check out the video on our lab channel below!

This post just goes to show you that we are all subject to error, and that we should take our mistakes with stride! What are some animal mistakes you've seen? 

BTW, Dan Deacon is a great artist who encourages audience participation at his shows and he also has a song called Snake Mistakes. Check it out here.

Happy early Thanksgiving to you all!

Wednesday, October 9, 2013

Disguised as the Enemy: Squirrels Use Snake Sheds to Mask their Scent

I passed my Ph.D. qualifying exam last Friday and I'm so glad that it's over! Please enjoy this fun little blog post I wrote to celebrate my advancement to candidacy. 

Several studies have shown that ground squirrels lick their fur after chewing shed rattlesnake skin. Many other animals have been shown to exhibit similar scent application behaviors (Table 1, Clucas et al. 2008b). Such behaviors are thought to transfer odiferous chemicals that repel potential parasites or predators onto the fur of the animal. Smelly fur may also affect the behavior of individuals of the same species (in social situations).  

The ground squirrels’ behavior of chewing snake sheds most likely masks their squirrelly odor from snake predators. Rattlesnakes have been shown to be more attracted the ground squirrel scent alone compared to ground squirrel scent mixed with rattlesnake scent (Clucas et al. 2008a). This supports the hypothesis that squirrels apply snake scent onto themselves to reduce the risk of rattlesnake predation. It’s a cool behavior that is often talked about, but rarely seen.

When shedding, snakes usually remain protected in their burrows. This is because the skin layer thickens over their eyes decreasing their ability to see and making them vulnerable to predation. Can you see how cloudy this snake's eyes are? He is just about to shed!

One morning this past summer, we came across a beautiful rattlesnake shed skin while radio-tracking Quirky Quinton (male northern Pacific rattlesnake). Quinton had literally just emerged from this shed; his body shape was beautifully preserved in it, and his scales were shiny and new. We took his shed with us to our field station camp and laid it out in the dirt. In no time, a squirrel pup emerged and starting performing the snake scent application behavior! This was very exciting for us because this behavior is rarely seen. We suspect that this is because squirrels prefer fresh sheds over old ones. Luckily our fresh shed induced this behavior and we recorded footage of it. Please enjoy watching the video of this rarely seen unique antipredator behavior.

Clucas, B., D. H. Owings, and M. P. Rowe. 2008a. Donning your enemy’s cloak: ground squirrels exploit rattlesnake scent to reduce predation risk. Proceedings: Biological Sciences 275:847–52.

Clucas, B., M. P. Rowe, D. H. Owings, and P. C. Arrowood. 2008b. Snake scent application in ground squirrels, Spermophilus spp.: a novel form of antipredator behaviour? Animal Behaviour 75:299–307.

Tuesday, September 17, 2013

Do Snakes Stress Out Squirrels?: Guest Post by Lauren Kong

Lauren is a graduate of Mills College where she was a Barrett Scholar last year. Her scholarship through the Barrett Research Program funded her stay with us at the Blue Oak Ranch Reserve. Her adviser at Mills, Dr. Jennifer Smith, is collaborating with me on a project examining the sub-lethal effects of snakes on ground squirrels. Lauren was in charge of data collection and organization for this project. She describes her research below: 

My research question focused on whether California ground squirrels (Otospermophilus beecheyi) were becoming stressed out after interacting with predatory snakes- the northern Pacific rattlesnake (Crotalus oreganus) and the Pacific gopher snake (Pituophis catenifer). To test our hypothesis we staged interactions between snakes and squirrels. We baited focal squirrels near snakes using sunflower seeds (their favorite food). After baiting the area, we waited until our desired ground squirrel approached and interacted with the snake. After the interaction, we trapped the squirrel using humane traps and collected their feces for the rest of the day. As a control treatment, we trapped the squirrel without having it interact with a snake and collected its feces to see if being in a trap affected their stress levels. To analyze the stress levels of squirrels that have and have not interacted with snakes, we will extract stress hormones (glucocorticoids) from their fecal material.

Ground Squirrel Perches on a Rock

It takes approximately 4-6 hours for the glucocorticoids to pass through the digestive system of the squirrel so it’s important to hold the squirrels long enough to get a complete sample. We placed the fecal deposits in tubes on ice or in liquid nitrogen. It’s important to collect the feces as soon as it is expelled because glucocorticoids are subject to degradation once they leave the body. Now that my internship is over, the fecal samples will be transported to the Smith Lab at Mills College for further analysis. We hope to see if venomous, and presumably more dangerous, rattlesnakes induce a greater stress response in squirrels than non-venomous, less dangerous gopher snakes.


We placed the squirrels onto plastic trays to collect their feces. Look at how many squirrels we did trials on in one day!

Although behavioral ecology can be taxing, this experience has opened my eyes to field biology. This research would not have been possible without the help of my fellow internists and Bree. Together we are a group of animal loving, enthusiastic, and intelligent people striving to elucidate the mysteries of animal life. This was a truly amazing experience. 

Looking over the edge of the Arroyo. Our study site is truly beautiful!

Wednesday, August 14, 2013

A Tale of Tails

After completing my summer field season on July 20th, I presented data from an experiment at the Animal Behavior Society meeting in Boulder, Colorado. I rushed to analyze the data (which was collected during the 2012 and 2013 field seasons) and create a PowerPoint presentation in less than one week! My goal was to present our "snake cannon" experiment which was designed to test how squirrels respond to simulated snake strikes. We hypothesized that tail-flagging squirrels would respond faster than non-tail-flagging squirrels if tail-flagging truly signals their readiness for a snake strike. Well, I successfully pulled together a beautiful presentation which was a huge hit at the meeting. It was such a success that National Geographic decided to write an article about it on their website. Please read the well-written article, A Tale of Tails, here

Sunday, July 7, 2013

Squirrels May Smell Out Snakes - guest post by Jenny Schefski

Jenny is one of my interns this summer, but she has been working with me since fall semester last year. She started reviewing video data from the 2012 field season, and now she is conducting her own independent project. She has graciously written a guest blog post describing her exciting research. See below:

This summer, I am studying the ability of California ground squirrels (Otospermophilus beecheyi) to detect and discriminate between two snake predators using olfactory cues. Thanks to the previous research of behavioral ecologists, it has been well established that California ground squirrels can visually recognize snakes along with snake-like patterns and objects.  Additionally, California ground squirrels have been shown to display distinct sets of behaviors towards the venomous northern Pacific rattlesnake (Crotalus oreganus) and the nonvenomous Pacific gopher snake (Pituophis catenifer).  However, little is known about their olfactory capabilities and what role olfaction might play in their detection and avoidance of snake predators.  Because gopher snakes and rattlesnakes are cryptic and often dwell in dark burrows, ground squirrels cannot always rely upon vision to detect them.  Therefore, it would likely benefit ground squirrels to have some sort of olfactory perception of snakes.   

I have strategically placed a rattlesnake model next to a squirrel burrow (top) 
and use snake tongs to handle a gopher snake model (bottom). 
Do you think they will fool the squirrels? 

To gain more insight into this fascinating predator-prey dynamic, I am filming ground squirrel interactions with visual and olfactory snake cues.  I create such cues by using rattlesnake and gopher snake models that are left unscented or scented with their respective odors. I place these snake models next to squirrel burrows and hope that squirrels interact with them.  I use security cameras to record squirrel interactions so that I can later quantify behaviors to see if visual detection of snakes is aided by olfactory and/or visual cues.  Additionally, I am scenting dirt with snake odors to see if grounds squirrels can detect snakes using olfaction alone.  Finally, I look forward to later quantifying the squirrels’ interactions with my treatments to see if they display different behaviors towards gopher snake cues versus rattlesnake cues.  

I position one of my security cameras over a squirrel burrow. I will leave it running 
all day to opportunistically record squirrels interacting with the rattlesnake model

I measure the distance of the model from the burrow

The snake model is set up (bottom right corner) and the security camera 
is set up to record squirrel encounters

The video footage I have reviewed so far is intriguing and looks promising.  I am excited to squeeze in as many trials as I can in my last two weeks here at BORR, and I look forward to reviewing all of my footage thereafter! 

Monday, July 1, 2013

Rattlesnake Researchers Knee-deep in Ponds?

Rattlesnakes are awesomely beautiful creatures that I greatly enjoy working with. However, every once in a while it’s nice to marvel at other animals for a change. Fortunately, we have many opportunities to learn about different animals in the area from the other researchers that utilize the Blue Oak Ranch Reserve. One such researcher is Rachel Anderson, a Ph.D. student in the Lawler Lab at UC Davis. I have known Rachel for over a year now; we first met on the UC Davis Odyssey (a GREAT grad student orientation trip that occurs every year). She just started her research examining the relationship between invasive bullfrogs and native California red-legged frogs. She came to BORR a couple of days ago and graciously let us tag along while she collected samples from a few of the ponds.  

 Rachel demonstrates how she catches bullfrogs

What a change it was for us! Rachel collects all of her data at night when it is easiest to catch frogs. In contrast, we work during the day, roughly from 7 am to 5 pm. I’m not going to lie; working at night is hard when you are accustomed to going to bed at 9 pm.  However, working in the cool night air was much better than the blazing hot sun. The most extreme change for us was actually getting wet! Many of us (including myself) had never waded in murky, muddy ponds so it was definitely a new experience. Rachel let us borrow waders, overall-like pants that prevent water from getting your clothes wet (that is, if you don’t go too deep). We dove right in (not literally) to help her spot frogs. One pond was so full of bullfrogs you almost could not avoid stepping on them. Rachel caught a few red-legged frogs and showed us their beautiful coloration. To my surprise, these frogs make one of the cutest sounds when they are captured, as if they are pleading with you to let them go. We also found a beautiful garter snake, and our most unexpected surprise was a rattlesnake! Joey, one of my interns, spotted a rattlesnake right next to the water. They are known to swim, but was this snake attempting to ambush frogs? It was indeed a strange encounter. 

Kissing prince charming

Lauren got a two-for-one

Pretty little garter snake

We did not return back to the field station until around midnight – awfully past our bedtime! We immediately passed out in our tents, exhausted from so much froggy excitement, and arose the next morning bright and early ready for another day of snakes and squirrels. 

Thursday, June 27, 2013

Guest Blog Post by Mike Hogan

The following is written by one of my field interns, Mike Hogan:

Ever since I can remember, snakes have captivated my interest and directed my academic focus in Biology and Herpetology. As a recent graduate of the University of Massachusetts Amherst, I jumped at the opportunity to work with the infamous North Pacific Rattlesnake as a summer field assistant. And after a month out in this beautiful reserve with great people and remarkable animals – life is good.

I find it amazing how much knowledge one can take away from studying a species. Just by looking at our research species, Crotalus o. oreganus, one could study behavior and discover evolutionary selective forces leading to such behaviors, or one could look at the venom and determine how regional distribution relates to toxicity and prey resistances, or one could sequence DNA from a number of specimens revealing gene flow, or record regional densities to establish the quality of various habitats… the list goes on. I think you can learn a lot by looking at one or two organisms and how they managed to combat selective pressures on our ever-changing planet.

Out of all the subfields of biology, behavior is definitely my favorite. I hope to someday incorporate snake behavior research into the venom industry, and observing free ranging predator prey interactions between ground squirrels and rattlesnakes is definitely an exciting step towards this goal.

Me, holding a tubed rattlesnake

But at the end of the day, the success of any research depends on the quality of the people involved with it. Each day I am surrounded by a group of hard working, compassionate field assistants with Bree as our fearless leader. A positive environment expedites the research, and I am glad to call myself part of such a great family here at BORR!

All the interns at the Oakland Zoo (on the day off of course)

Below is a quick video I put together using some footage I collected while in the field. Enjoy! 

Sunday, June 23, 2013

Meet the 2013 Interns!

From left to right: Mike (with one of our snake buckets and tongs), Jenny (with a boar's jaw), Lauren (with a gopher snake), Susan (with a kingsnake), and Joey (with a ring-necked snake)

Every year I take on several undergraduate field interns to help me with my research. This year I have 5 assistants from all over the United States. By working with me, they are hoping to gain valuable field experience that will prepare them for graduate school. In my opinion, they will learn more field techniques and research skills in their 8 weeks here than any college course can offer. 

Lauren shows
that snake bag 
can double as a
hat when needed

They work more than 12 hour days, 6 days a week. Every day, they perform several research tasks: radio-track the 20 tagged rattlesnakes, trap and mark squirrels, conduct behavioral observations and experiments on squirrels, collect measurements of squirrel temperament, help with presenting Robosquirrel to hunting rattlesnakes, just to name a few. They learn the difficulties that come with working in the field, the amount of effort it takes to collect behavioral data (for example only getting 1-2 samples per day), both of which lead to the surprising realization that research sounds so much simpler on paper than when being tested in person.  

I am very proud of them and I have asked each of them to write guest posts for my blog. Stay tuned for their thoughts on squirrel-snake interactions and how they find the field experience. I appreciate their hard work; after all, my research could not be done without them!

Joey transports a snake from a 
bucket to its glass terrarium 

Saturday, June 15, 2013

Good Friends and Snake Venom

My good friends, Matt Holding and Sloan Henningsen, paid a visit to our field site last week. Matt and I know each other from working in Dr. Emily Taylor’s lab at Cal Poly. Sloan is his awesome significant other and they make quite a terrific field team. Matt is now a Ph.D. student in the Gibbs Lab at The Ohio State University and we are collaborating on a project examining squirrel venom resistance and rattlesnake venom toxicity.

Many people do not know that ground squirrel blood contains proteins that neutralize rattlesnake venom. This means they can fight off the effects of envenomation, but are not immune (like how your body can fight off a cold). The level of resistance in squirrels correlates with blood volume – therefore pups are more susceptible to death by envenomation than adults. It was long thought that adults were essentially free from rattlesnake predation because of their resistance, but our research has shown that adults are commonly preyed upon by snakes.

Images of rattlesnake bite wounds from two different populations of ground squirrels. The top image shows the wound (circled in white) of a California ground squirrel with venom resistance. The bottom image show a wound caused by the same amount of venom in a squirrel without venom resistance.** 

For his dissertation, Matt is examining venom resistance in several populations of California ground squirrels.  My field site at BORR is one of the populations he is sampling from.  We are excited to see the composition of rattlesnake venom in relation to squirrel blood resistance especially since adult squirrels are eaten by snakes at our site. We are also interested in examining the individual variation in resistance (how resistance differs from squirrel to squirrel) and if this variation correlates with squirrel anti-snake behaviors (tail-flagging, alarm calling, substrate throwing, etc.).

Matt demonstrated several of his extraction methods while he visited us. Please enjoy the pictures below. Also, check out his awesome blog here.

 We scare a trapped squirrel into a bag

 Matt puts the squirrel under using a light anesthetic 

I measure various body parts on the squirrel

 Matt tubes a rattlesnake

We draw blood from the snake 

 Matt collects its venom (you can see some in the bottom of the glass)

**Image from: Owings, D. H., and R. G. Coss. 2007. Hunting California Ground Squirrels: Constraints and Opportunities for Northern Pacific Rattlesnakes. Biology of the Rattlesnakes.

Monday, June 10, 2013

The Field Season 2013 Begins!

Hi all!

I was finishing up my coursework the past months, but now I am back in business! The field season started three weeks ago and we are chugging along slowly but surely. I have five field interns working with me and they are wonderful additions to Team Crotalus (fyi - Crotalus is the genus for the rattlesnakes). This field season, our main focus is to conduct two field experiments testing the function of squirrel tail-flagging. We hypothesize that squirrels tail-flag to rattlesnakes to signal their vigilance and readiness to evade a snake strike. If this is true, (1) squirrels should evade snake strikes more often when tail-flagging and (2) snakes should strike less often at tail-flagging squirrels. We present a device to squirrels that simulates a snake strike to test prediction 1(see images below), and we use Robosquirrel to test prediction 2.  These experiments may sound simple, but working with wild animals can be unpredictable and frustrating (because they do not cooperate with you). It will likely take all summer to collect a large enough sample size to test our hypothesis.  

Screen shots from a trial with the strike simulating device. The focal squirrel is circled in red in the upper shot. At 0.00 seconds, the spring within the device (indicated by the yellow arrow) has not been released. By 0.58 seconds, the spring has been released and the squirrel has evaded it.

In addition to performing the abovementioned field experiments, we radiotrack 20 wild rattlesnakes each day. Since snakes are secretive and elusive creatures, we would not be able to understand how they interact with squirrels without knowing where they are at all times. We often catch glimpses of interesting behaviors because we track them so often. Please enjoy the video below that my intern, Mike, made showing the radio-tracking process and a great observation we made on our first day out in the field.