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.