Tuesday, October 14, 2014

My Second Publication Has Video of Ninja Squirrels

So…it’s been a while since I blogged mainly because there hasn’t been much to write about. My summer field season was suuuppper slow and filled with many road bumps. Snakes, unfortunately, are not very active during drought times (just ask Mike Cardwell). However, I have been working on a post about an extraordinary rattlesnake behavior that I recorded in three individuals; cannot give you any details at the moment, but I plan to write a Herpetological Review article about it once I gather more insight from other snake researchers. Stay tuned. Anyway, this post is not about that, but about the first publication to stem from my dissertation research (and my second publication overall). Woohoo!

When they encounter a rattlesnake, squirrels approach it and waive
their tails back and forth (a behavior aptly called tail flagging)

Squirrels tail flag (a vertical side-to-side motion of the tail) to deter snake predators (both rattlesnakes and gopher snakes). Tail flagging deters snakes because it signals to them that they have been discovered, and because snakes rely on surprise to attack prey, their likelihood of hunting success drops significantly. So after receiving tail flagging displays from squirrels, snakes relocate to a new hunting site where prey are unaware of its hidden location (Barbour and Clark 2012). There’s just one problem with tail flagging: squirrels use it most often when no snake is present. Are squirrels dishonestly advertising their discovery of a snake? This was the question I sought to answer.

Is tail flagging a dishonest signal?

Many animals use signals similar to tail flagging to advertise their awareness of predators. However, these animals also exhibit their signals when predators are absent. This is a common phenomenon!
Just like ground squirrels, these two bird species, the moorhen 
(left) and motmot (right), flick their tails in the absence of predators.

Why would animals signal to predators when no predator is around? The idea is that they are not signaling their awareness of a predator, but their readiness for a surprise attack from hidden predators (this is also called vigilance). Vigilant animals that are prepared for an attack should be harder to catch than non-vigilant animals. But in order to test the hypothesis that animals signal vigilance in the absence of predators, we need to simulate predator attacks on signaling and non-signaling prey and then record their responses. We predict that signaling prey will escape more effectively than non-signaling prey. 

Unaware individuals should not respond effectively to surprise attacks.

And so this is exactly what I did! I simulated rattlesnake strikes on tail-flagging and non-tail-flagging squirrels and filmed their responses using a high speed video camera. You may be wondering how I simulated a snake strike. Well, I didn’t have to do too much work because a strike-simulator already exists on the market and it’s called the “Snake in a Can Prank.”

Inspiration for the strike-simulating device

I modified these prank toys and shot them at unsuspecting squirrels. I tested squirrel responses to the strike-simulator under three treatments that affected their tail-flagging: 1) No Snake Present, 2) Snake Present, and 3) Recent Snake Encounter. Most squirrels did not tail flag when no snake was present (No Snake), squirrels actively interacted with a present rattlesnake (Snake Present), and squirrels maintained tail flagging behaviors after recently encountering a snake that was no longer present (Recent Snake). The Recent Snake treatment is unique because it decouples the effect of predator presence from tail flagging.  

And now…the Results. Squirrels in the Recent Snake treatment (tail flagging in the absence of predators) were more effective at evading surprise attacks than squirrels in the other two treatments. This was just what I expected. Tail flagging in the absence of snakes associated with faster reaction times and escape speeds. 

Two figures from my study. Squirrels in the Recent Snake treatment reacted
faster and displaced their bodies more quickly (quicker escape speed) than
squirrels in the other two treatments.Letters indicate differences between
groups (no difference between 
Snake Present and No Snake
Furthermore, these squirrels used unique ninja-like maneuvers to flee from the attack (unlike squirrels in the other two treatments which mostly ran away from the attack). Vigilant squirrels leapt either vertically or horizontally, contorting their bodies, and using their tails to propel them through the air. This type of flee maneuver makes sense if one is trying to escape a rattlesnake strike. Strikes are extremely fast, but once a snake strikes, it cannot alter its strike trajectory. Thus, it’s better to move outside of the plane of the strike than the try to outdistance it (which is probably ineffective considering the speed at which a rattlesnake can strike). 

Squirrels in "ninja-mode" use evasive leaps to escape simulated snake strikes. This occurs most often when squirrels have
 encountered a snake, but then no longer know where it is (because it has been removed). 


My study called, The fear of unseen predators: ground squirrel tail flagging in the absence of snakes signals vigilancecan be found in a future issue of the journal, Behavioral Ecology. Advanced access to this publication can be found here

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