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.

2 comments:

  1. I've always thought that scavenging was more common in snakes than generally realized. They must have good immune systems!

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  2. Very nice article, really great infomrmation

    ReplyDelete