Ground squirrel tail-flag displays alter both predatory strike and ambush site selection behaviours of rattlesnakes

Abstract

Many species approach, inspect and signal towards their predators. These behaviours are often interpreted as predator-deterrent signals-honest signals that indicate to a predator that continued hunting is likely to be futile. However, many of these putative predator-deterrent signals are given when no predator is present, and it remains unclear if and why such signals deter predators. We examined the effects of one such signal, the tail-flag display of California ground squirrels, which is frequently given both during and outside direct encounters with northern Pacific rattlesnakes. We video-recorded and quantified the ambush foraging responses of rattlesnakes to tail-flagging displays from ground squirrels. We found that tail-flagging deterred snakes from striking squirrels, most likely by advertising squirrel vigilance (i.e. readiness to dodge a snake strike). We also found that tail-flagging by adult squirrels increased the likelihood that snakes would leave their ambush site, apparently by elevating the vigilance of nearby squirrels which reduces the profitability of the ambush site. Our results provide some of the first empirical evidence of the mechanisms by which a prey display, although frequently given in the absence of a predator, may still deter predators during encounters.

The ontogeny of antipredator behavior: age differences in California ground squirrels (Otospermophilus beecheyi) at multiple stages of rattlesnake encounters

“…Barbour and Clark (2012) found that the more time adult squirrels spent signaling toward a rattlesnake, the more likely the snake was to leave the area. In contrast, after interactions with squirrel pups, snakes were more likely to remain in the area and their likelihood of capturing a pup increased.…”

“…We quantified two distinct flee modalities that squirrels used to evade simulated strikes: evasive leap, a vertical or sideways jump in the air with all four feet off the ground while swinging the tail, or scramble, during which squirrels ran away without leaping into the air. Evasive leaps were qualitatively similar to the escape maneuvers squirrels use in response to free-ranging rattlesnake strikes (Hennessy and Owings 1988;Barbour and Clark 2012). For each trial, we also quantified tail-flagging rate by counting the number of tail-flagging bouts that occurred the minute before the release of the spring.…”

“…Ground squirrels usually occupy a small home range around their home burrows; the diameter of the core use area of adult females is approximately 9 m, while the diameter of the core use area of adult males is approximately 5 m (Boellstrorff and Owings 1995). We assumed encounters that occurred more than 9 m apart involved separate individual squirrels (see Barbour and Clark 2012). Snakes moved, on average, 34.6 m (range, 9.8-154.0 m) between hunting locations, so most recordings were well over 9 m apart.…”

“…Tail flagging deters snakes from striking by signaling the squirrel's vigilance; it also causes snakes to abandon the area by increasing vigilance in nearby prey (Hasson 1991;Barbour and Clark 2012;Putman and Clark 2015). Even if a snake strikes, squirrels may still avoid injury or death because they have evolved the ability to rapidly leap away from an attack, and tail flagging also informs snakes that a squirrel is prepared to jump (Owings and Coss 2008;Putman and Clark 2015).…”

Isolation rearing reveals latent antisnake behavior in California ground squirrels (Otospermophilus becheeyi) searching for predatory threats

“…Tail flagging occurs almost exclusively after ground squirrels have detected snakes (Hennessy et al 1981). It also occurs if squirrels are likely to encounter snakes (Barbour and Clark 2012;Hersek and Owings 1993). Thus, it is reasonable to assert that nest-box opening inspection and tail-flagging activity by the laboratoryreared squirrels characterized anticipation that a snake was lurking inside its nest box.…”