Park Visitor Victoria Párraga whipped out her cell phone and caught video of a Ground Squirrel attacking the tail of a full size Gopher Snake. Victoria’s friend Emilie Keas also took a couple of snapshots that highlight the David v. Goliath misproportion between the two creatures.
Ground squirrels and snakes both live on the ground and inhabit burrows. They’ve developed a complicated relationship. Gopher snakes hunt and kill small burrowing mammals, and are regular predators of Ground Squirrels. The squirrels, however, return the favor. Although primarily vegetarian, they’ve been known to feed on gopher snake eggs and new hatchlings.
Ground Squirrels are experts at dealing with a much more formidable reptile: rattlesnakes. There aren’t any in the park, but out in the wild where Ground Squirrels maintain big colonies, rattlesnakes are frequent visitors. Adult Ground Squirrels quickly develop immunity to rattlesnake venom. They also chew discarded rattlesnake skins and then lick their fur to apply the snake scent. They have other tricks as well, detailed in this excellent Oxford Academic article:
Otospermophilus beecheyi uses a novel form of chemical defense by directly applying heterospecific substances to its body; it chews skins shed from rattlesnakes and then licks its fur to apply the scent (Clucas et al. 2008a). Female squirrels with young also lick their vulnerable young to apply the scent (Clucas et al. 2008b). Juveniles and adult females engage in longer bouts of application than do adult males, a finding that Clucas et al. (2008b) suggest is likely attributed to the fact that young are more vulnerable than juveniles to predation, and adult females actively protect young.
Because O. beecheyi is diurnal and has an acute visual system, it primarily relies upon the production of visual pursuit-deterrent signals when coping with snakes (Owings and Coss 1977). Squirrels often assume the bipedal alert posture after climbing a “promontory,” such as a log or stone; increased height presumably allows for increased visibility of the surroundings (Owings et al. 1977). Upon detecting a snake predator, a squirrel increases its vigilance and often rears up on alert as a defense mechanism (Putman and Clark 2015). O. beecheyi is most vigilant if it recently encountered a predator and, on average, a vigilant squirrel reacts more quickly and escapes more effectively in response to simulated snake strikes than does a nonvigilant squirrel (Putman and Clark 2015).
Otospermophilus beecheyi also engages in a number of stereotyped visual displays when it encounters a live snake, presumably to gain information about the snake and to attempt to remove it from the area. It often directly harasses and approaches snakes by elongating its body to taunt the snake and then quickly jumping back to avoid capture (Fig. 5A; Owings and Coss 1977). Field experiments in San Diego County, California using snake replicas (made of plasticine) suggest that O. beecheyi distinguishes between the risks associated with snakes, directing the most intense and frequent aggression towards the heads of small snake replicas, but only mild aggression towards the tail of large snake replicas (Mitrovich and Cotroneo 2006). Confrontational behaviors are used especially to distract snakes away from burrows containing young; these include squirrels kicking sand towards, pouncing on, or even biting the snake (Fig. 5A; Owings and Coss 1977). Squirrels may also plug tunnels or burrow entrances to deter snakes (Coss and Owings 1978).
Otospermophilus beecheyi regularly engages in a snake-directed pursuit-deterrent signal, called tail-flagging; this consists of side to side motions of the elevated, piloerected tail to signal to snakes that the squirrel has detected the snake’s presence (Owings and Coss 1977; Hennessy et al. 1981). Tail-flagging serves as a warning signal to other squirrels in the area and communicates to the snake the squirrel’s detection of the hidden predator along with its vigilance and readiness to leap away (Putman and Clark 2015). As in many other species of small animals that encounter snakes, O. beecheyi uses vertical or lateral evasive leaps to avoid snake strikes (Fig. 5B; Putman and Clark 2015).
Otospermophilus beecheyi also modulates its tail temperature when tail-flagging at rattlesnakes but not when tail-flagging at gopher snakes (Rundus et al. 2007). That is, O. beecheyi increases its tail temperature when interacting with rattlesnakes, which are able to detect thermal cues using a pair of facial heat-sensing pit organs, but not at gopher snakes lacking pit organs and thus the ability to physiologically detect thermal information produced by squirrels (Rundus et al. 2007). Barbour and Clark (2012) indicated that rattlesnakes are indeed less successful in striking tail-flagging squirrels, suggesting that the infrared tail-flagging by squirrels diverts the strike away from the body of the squirrel.
Bottom line: this episode of a squirrel attacking a snake, although never recorded before in the park, is part of the long-evolved relationship between these two burrowing neighbors. Thanks to Victoria and Emilie for sharing these images.