Tuesday, May 20, 2014

Daredevil Gopher Snake Gets Rescued!

I arrived at my field site (Blue Oak Ranch Reserve) a little over a week ago. Work has been pretty slow as we are trying to capture rattlesnakes to implant radio transmitters into. Three days ago, we ended work early and were hanging out at the field station (a large barn). I noticed snake-like slithering near the roof of the barn so I looked up. Lo and behold a gopher snake (Pituophis catenifer) had weaseled its way (or shall I say “snaked” its way) about thirty feet up the barn wall! At first, I thought this sight of the wall-climbing snake was strange, but then I realized that it was heading straight towards a bird’s nest. I became extremely excited as I had never seen a snake ambush birds before. I got out my camera and started to record the snake.


Although I mainly think of gopher snakes as ambushing squirrel pups inside their burrows, these snakes are common bird nest predators, and will go for both cavity-nesting and open-nesting bird species. A study performed by Eichholz and Koenig In central California (1992) found that approximately 21% of bluebird nests and 36% of nest failures are caused by snakes, making snakes the primary cause of nest mortality. They also found that gopher snakes do not randomly search tress for nests, but only climb those with active nests. This suggests that they have the ability to detect bird nests from the ground (probably by picking up chemical cues). These snakes seem to prefer eating baby birds instead of eggs, and their preference increases as the babies grow older. Another report by Czaplewski et al. (2012) describes a gopher snake making a dangerous climb to ambush cliff swallow nests in Utah. The authors’ note the appearance of several small food items in the snake’s belly.

 Gopher snake browsing on cliff swallow morsels (taken from Czaplewski et al. 2012)


Back to my story, the snake appeared to be entering the bird nest when it suddenly became very still. I waited for it to continue its movement into the nest, however it started to twist and squirm. It had become tangled in plastic mesh netting on which the nest was built. Unable to reach the snake, I thought for sure it would die.

If only snakes could use ladders, then bad things wouldn't happen...
(http://pixabay.com/en/snake-cartoon-game-ladder-python-36376/) 


As it remained motionless stuck within the netting, a wren approached the snake and made loud calling sounds. This could have been the mother bird defending her eggs. Many birds will make specific alarm calls in response to snake predators. A recent study shows that Japanese great tits (Parus major minor) produce alarm calls that encode information about the type of predator (Suzuki 2014). These birds use a “jar” call for snake predators and a “chicka” call for crows and martens (a type of weasel). These calls are thought to warn offspring and other birds, but they may also deter the snake from further pursuit of the nest (something called pursuit-deterrent signaling). My current research examines the use of pursuit-deterrent signaling in California ground squirrels against rattlesnake predators.

View the whole gopher snake story on the Youtube video above!

The gopher snake remained stuck in the mesh netting near the roof of the barn, and I thought for sure it would die. However, Erik, the reserve steward came to the rescue! He found a tall ladder that he used to reach the snake and remove it from the barn wall. The snake remained tangled in the mesh and we had to cut it out. Poor snake had ripped some of its skin open trying to free itself. I applied anti-septic liquid bandage to its cuts, and am now keeping it in captivity so that its skin can heal. I will release it soon so it may resume its daredevil climbs.

Erik was this snake's "knight in shining armor" 


 The gophie really did a number on itself. Luckily, we were able to cut away the mesh.

------------------
References:

Czaplewski, N. J., K. S. Smith, J. Johnson, C. Dockery, B. Mason, and I. D. Browne. 2012. Gopher Snake Searching Cliff Swallow Nests in East Central Utah. Western North American Naturalist 72:96–99.

Eichholz, M. W., and W. D. Koenig. 1992. Gopher Snake Attraction to Birds’ Nests. The Southwestern Naturalist 37:293–298.

Suzuki, T. N. 2014. Communication about predator type by a bird using discrete, graded and combinatorial variation in alarm calls. Animal Behaviour 87:59–65.

Monday, May 12, 2014

To Detect a Predator: A Multimodal Approach

This is another guest post from undergraduate scientist, Jenny Schefski. She previously wrote a post on this blog last summer when she was conducting research for her independent project (read the post here). Now, she elaborates more on the concept behind her research and why it is important. 

As humans, we rarely need to rely on all of our senses to find food, shelter, or mates. Indeed, these necessities are often advertised and/or delivered to us with little effort. With virtually no predators, we aren’t even likely to need our senses to avoid becoming prey. 


Unlike wild animals, most people have little trouble finding food, shelter, or even mates.
(http://www.brennersigns.com/wp-content/uploads/2012/12/hotel-led.jpg, http://listabuzz.com/wp-content/uploads/2013/12/match.jpg)


Unless you’re unlucky enough to encounter Hannibal, you probably aren’t too concerned about becoming a predator’s next meal.
(http://ic.pics.livejournal.com/cleolinda/1427760/456345/456345_600.png)


However, most animals heavily rely on their senses to avoid predators, and to find food, shelter, and mates. By utilizing multiple senses, animals increase their likelihood of success in a variety of conditions. Sharks, for example, are capable of using a wide array of senses to locate prey.1 This is especially important in the ocean since prey can be sparse and visibility can be poor. By utilizing multiple senses to find their prey, sharks maximize their likelihood of foraging success.

Sharks maximize their hunting efficiency by using multiple senses to track down prey.
(http://www.nature.com/scientificamerican/journal/v297/n2/images/scientificamerican0807-74-I4.jpg)


The use of multiple senses to gather information about one’s environment is called multimodality.2 Multimodality is important to the study of animal interactions because multiple sensory inputs can lead to complex behaviors. In simpler terms, a noise from Animal 1 might result in a specific behavior from Animal 2. However, the scent of Animal 1 might lead to a different behavior from Animal 2. 

Let’s say a= a snake’s pattern, and b= a snake’s scent. The shapes that follow the arrows represent all of the possible response behaviors from a hypothetical squirrel. (Partan & Marler 2005).


Predator-prey interactions often involve complex behaviors. In order to avoid becoming a predator’s next meal, prey must be able to identify and detect their predators.  Over millions of years, prey have fine-tuned many of their senses to the detection of specific predators. For example, wolf spiders can detect the specific frequency of vibrations from their bird-predator’s pecking on a tree.3  Spiders that were experimentally exposed to the pecking frequency stopped all courtship behaviors and movement. Even more, wolf spiders also respond to the shadow of a bird predator; except, in this case, they increased locomotion and escape behaviors. This study is not only a prime example of how prey can detect sneaky predators, but also how multimodal interactions can lead to complex outcomes.

Wolf spiders can identify and respond to the pecking, calling, and even shadow of a bird-predator. Of course, there are always prey that miss the memo(s). This unfortunate wolf-spider probably should have paid more attention to his senses.  

Not only is multimodality important for predator detection, but it is also key for species discrimination. For example, brown anoles can detect their bird-predator, the grackle, by sight and by sound.4  Throughout the day, brown anoles see and hear multiple birds. So how can they know when to hide or when it’s safe to do important things like forage or look for a mate?  Since the anole can identify the grackle’s specific appearance and call, it can discriminate between the grackle and other non-threatening birds. By having the ability to cue-in on the grackle using multiple senses, the anole can maximize its time to forage and search for a mate, and minimize its likelihood of becoming a grackle’s next meal.

Brown anoles can identify the appearance and call of their predator, the great tailed grackle. This ability allows anoles to distinguish the grackle from non-threatening birds so they don’t have to hide all day.
(https://c1.staticflickr.com/5/4086/5066322444_44a14302a2_z.jpg, http://www.planetofbirds.com/wp-content/uploads/2011/07/Great-tailed-Grackle.jpg)


Another predator-prey system that is ideal for the study of multimodal predator detection and discrimination is that of the California ground squirrel. California ground squirrels have two snake-predators: the Pacific gopher snake and the northern Pacific rattlesnake. Gopher snakes are non-venomous and rely on their stealth to invade squirrel burrows in search of pups. Conversely, rattlesnakes are venomous and can quickly kill both pup and adult squirrels. Since each snake poses a different level of immediate risk, it would behoove ground squirrels to not only identify a snake predator, but also discriminate between a venomous and non-venomous one. 

California ground squirrels have two snake-predators: the northern Pacific rattlesnake (top) and the Pacific gopher snake (bottom). Rattlesnakes are more threatening to squirrels because of their ability to quickly inject squirrels with deadly venom. (Photos: Joseph Chase)


Previous studies show that ground squirrels do indeed discriminate between gopher snakes and rattlesnakes.5 This is evidenced by squirrels’ behavior toward each snake species. Ground squirrels tend to be more aggressive toward gopher snakes and will approach them more closely. When presented with a rattlesnake, ground squirrels are likely to monitor it more often, but maintain more distance from it.

Exactly how California ground squirrels discriminate between each snake-predator remains unclear. We do know that squirrels can identify each snake by its visual appearance.5 However, there are a variety of reasons why vision is not always a reliable mode of detection for ground squirrels. Not only do squirrels often encounter snakes in their very own, dimly lit burrows, but they also encounter them often in dense vegetation. Furthermore, both rattlesnakes and gopher snakes blend into their surroundings very well. All of these factors suggest that squirrels might use another sense to detect each snake and discriminate between the two species.

Can you find the snakes in these photos? California ground squirrels often encounter snakes moving through the grasses that they feed on. Spoiler: a gopher snake (left) and a rattlesnake (right). (Photos: Joseph Chase)


My research focuses on how California ground squirrels use multiple senses to detect and discriminate between gopher snakes and rattlesnakes. One previous lab study suggested that California ground squirrels can identify the scent of each snake-predator.6 My work takes this study to the field, a more realistic setting. By manipulating the scent of rattlesnake and gopher snake models, I can tease apart the role of each cue in squirrel response behavior. My ongoing analysis has led me to many questions: Does the smell of a snake make squirrels more wary of their environment or does it elicit anti-snake behavior? What will squirrels do when presented with a rattlesnake model that smells like a gopher snake? Do squirrels trust visual or olfactory input more when deciding how to react to a snake predator?

I am still in the process of analyzing seemingly endless field footage, but I hope to have some answers soon!

---------------
References:

1.  Hueter, R.E., D.A. Mann, K.P. Maruska, J.A. Sisneros, and L.S. Demski. 2004. Sensory Biology of Elasmobranchs. Biology of Sharks and Their Relatives 1: 326-358.

2. Partan, S.R. and P. Marler. 2005. Issues in the classification of multimodal communication signals. The American Naturalist 166:231-245.

3.  Lohrey, A.K., D.L. Clark, S.D. Gordon, and G.W. Uetz. 2009. Antipredator responses of wolf spiders (Araneae: Lycosidae) to sensory cues representing an avian predator. Animal Behaviour 77:813-821.

4.  Elmasri, O.L., M.S. Moreno, C.A. Neumann, and D.T. Blumstein. 2012. Response of brown anoles Anolis sagrei to multimodal signals from a native and novel predator. Current Zoology 58:791-796.

5.  Towers, S.R. and R.G. Coss. 1990. Confronting snakes in the burrow: snake-species discrimination and antisnake tactics of two California ground squirrel populations. Ethology. 84:177-192. 

6.  Hennessy, D.F. and D.H. Owings. 1977. Snake species discrimination and the role of olfactory cues in the snake-directed behavior of the California ground squirrel. Behaviour. 65:115-123.

Monday, March 31, 2014

Seeking Field Assistants

Field assistants needed for my research - starting mid-May

Study on the antisnake behavior in California ground squirrels and its implications for hunting rattlesnakes

Location: Blue Oak Ranch Reserve, California (www.blueoakranchreserve.org)

Dates:  Middle of May through July (approx. May 15th-July 20th 2014)

Job description:  The Clark lab at San Diego State University is seeking motivated individuals to assist in a behavioral study on predator-prey interactions between northern Pacific rattlesnakes (Crotalus oreganus oreganus) and California ground squirrels (Otosperomphilus beecheyi).  Individuals will live and work with other field assistants at the Blue Oak Ranch Reserve in the foothills east of San Jose, California.  Assistants will help with capture and radio telemetry of rattlesnakes, implementation of fixed videography in the field, and behavioral experiments on wild animals. This a great opportunity to gain experience with trapping, marking and handling of animals, radio telemetry, GPS, videography, and other basic behavior and ecology field techniques.

Qualifications:  No experience necessary, but applicants with lab or field research experience will be given priority. On-the-job training will be provided.  Must be able to hike long distances over rough terrain carrying heavy equipment, conduct patient observations for long periods of time (up to 10 hours/day), and live in a remote wilderness area with primitive facilities. Must be able to work and live comfortably in variable environmental conditions including both cold/hot weather and in tick/mosquito habitats. Must be passionate about science, hardworking, independent, good-natured, love working in the outdoors, and able to share close living quarters with other researchers. Room and board (research facility fees and food) are provided, but interns will be required to sleep in tents for the entirety of the field season.

Application:  Please apply by April 15th. To apply, please send a cover letter and resume (including contact information for three references) detailing your experience with field biology, outdoor skills, and animal behavior to Bree Putman at:  breeput@yahoo.com 

Tuesday, March 25, 2014

A Snake's Scavenger Hunt

The way you eat probably doesn't change much daily. Sure, you have to make a few decisions like whether you should go out, get delivery, or make food at home. You also must decide whether to eat with your hands or silverware, at the dining room table or on the go. But overall, your mode of eating generally consists of preparing a meal which you take approximately 10 minutes to consume while sitting down, and as with most things in life, there are exceptions to this rule (like Adam Richman of Man Vs. Food). 

This man is an exception to the "human foraging mode"
(http://community.babycenter.com/post/a28159269/man_vs_food)

Unlike humans, snakes have two main foraging modes called ACTIVE and AMBUSH (or sit-and-wait). Active foraging consists of actively searching for and pursuing relatively immobile prey (e.g. sleeping or resting prey, or prey such as newborn animals). Ambush foraging consists of remaining at a hunting site for several hours to days to opportunistically attack prey that passes by. Active foragers generally have high endurance, but also high energy demands, while ambush foragers are low energy specialists, but have low endurance. 

Characteristics of the two main foraging modes in snakes
(http://uts.cc.utexas.edu/~varanus/ForagingTactics.html)


Browsing is also recognized as an alternative hunting mode in some snakes. For instance, Turtle-Headed Sea Snakes (Emydocephalus annulatus) in New Caledonia swim slowly searching for fish nest eggs in crevices along the ocean bottom (Shine et al 2004). A fourth foraging mode in snakes is less understood: SCAVENGING! Many people have described scavenging in snakes, but few have conducted formal studies on this interesting behavior (I could only find one during a quick literature search). Snakes are thought to employ scavenging opportunistically, eating carrion (dead decaying animals) only when chance allows. The one study I found showed that Western Diamondbacks (Crotalus atrox) were willing to consume mice that had been dead for 48 hours, but Black Rat Snakes (Elaphe obsolete) were not. The Diamondback rattlesnakes could even locate dead mice hidden within gravel (probably using their sense of smell).   

(http://www.tigerscursebook.com/blog/post-203/)

A review in 2002 by Devault and Krochmal found 39 published accounts of scavenging in snakes, which in total yielded 50 observations of this behavior. I’m sure that more than 10 years later, this number has increased. They found that pit vipers (snakes in the family Crotalinae) and piscivoruous snakes (those that eat fish) were most commonly reported as scavenging. Scavenging was also not limited to one prey type. What still remains unclear is what percentage of snakes’ total diet consists of scavenged carrion. This question is nearly impossible to answer with traditional snake diet studies that examine gut contents. As you can imagine, it is extremely hard to determine whether digested material in the gut came from freshly killed prey or carrion. One would need to literally observe a snake’s foraging behaviors 24/7 to answer this question.


The research we conduct in the Clark Lab attempts to expand our knowledge on rattlesnake (Crotalus oreganus) foraging behavior and diet with the use of fixed videography. Cameras overlooking snakes record their behaviors for prolonged periods of time, sometimes capturing rarely observed events. I am pleased to announce that this past summer (2013), we finally found a scavenging rattlesnake! Ironically, we did not discover this snake with our fixed video cameras, but by chance. Watch Iggy scavenging on my YouTube channel!



We found Iggy, a pregnant female northern Pacific rattlesnake on May 23rd at 11:46 am. She was scavenging a decapitated ground squirrel pup lying on the edge of a dirt road. She attempted to eat it several times over 7 minutes. She also dragged its body 16 meters from its initial location. Iggy had a hard time consuming the dead pup probably because it was missing its head, and snakes mostly consume their prey head-first. From our video recordings of her attempting to consume the pup, it seems that she was able to locate the anterior (front) region of the body, but could not get a good enough grip to start the consumption process. Eventually she gave up on it and slithered into the shade of a burrow.  


References:
Devault TL, Krochmal AR (2002) Scavenging by snakes: an examination of the literature. Herpetologica 58:429–436.

Gillingham C, Baker E (1981) Evidence for Scavenging Behavior in the Western Diamondback Rattlesnake (Crotalus atrox). Zeitschrift fuer Tierpsychologie 55:217–227.

Lillywhite HB, Sheehy CM, Zaidan F (2008) Pitviper Scavenging at the Intertidal Zone: An Evolutionary Scenario for Invasion of the Sea. Bioscience 58:947–955.

Shine R, Bonnet X, Elphick MJ, Barrott EG (2004) A novel foraging mode in snakes: browsing by the sea snake Emydocephalus annulatus (Serpentes, Hydrophiidae). Funct Ecol 18:16–24.