Landels-Hill Big Creek Reserve

09 Jul, 06 AM - 11 Jul, 10 AM

California ground squirrels (Spermophilus beecheyi) encounter a multitude of predators in their natural habitats, and among the most commonly encountered include the Pacific rattlesnake (Crotalus oreganus), and the Pacific gopher snake (Pituophus catenifer), as well as a variety of larger mammalian predators and birds of prey. California ground squirrels have thus been exposed to a complex predator-avoidance selective pressure which must have been tailored to deter predation by animals occupying very specific microhabitats, leading them to devise special circumvention techniques to help them deal with distinctive avenues of attack. Among their specialized predator-deterrence capabilities are alarm vocalizations that are thought to communicate the presence of certain predators, composite visual signaling systems in the form of tail-flagging that can convey information directly to predators and conspecifics, a functional budgeting of the time spent in heightened states of vigilance and investigation of possible danger, and finally a reasonably well-developed ability to avoid physical contact from the hazards of their environment. As burrowing and ground-dwelling animals, California ground squirrels are primarily in danger of predation by Pacific rattlesnakes and Pacific gopher snakes, as these predators not only are found in high densities, but they happen to occupy the same microhabitat and frequently inhabit squirrel burrow systems. As a result, ground squirrels contribute a comparatively large amount of their time eluding their advances, frequently investigating suspect areas such as dark burrows and scattered deadfall, and have also been known to identify snake-like patterns from several meters away. After identifying a snake, ground squirrels maintain a heightened level of vigilance that can last for considerable amounts of time, which may facilitate spatial and temporal recognition of the identified threats. Adult ground squirrel populations from the Diablo Mountain Range in San Jose, CA were selected for field presentations that effectively mimicked snake predation situations in order to measure states of vigilance as a function of predator type. Adult squirrels were shown live tethered Northern Pacific rattlesnakes and Pacific gopher snakes, ceramic models of the respective snake species in question, as well as novel, decontextualized objects, within specific bait arenas. The main goal was to acquire a detailed description of the behavioral organization that follows the activation and sustainment of the sympathetic nervous system when squirrels encounter snake predators of different species, in order to better understand the relative responsiveness and efficacy of the heightened vigilance in identifying snake-like objects in future encounters. The time spent in characteristic states of fixed investigations of the presented stimuli were considered and analyzed as a function of the stimulus, and an arousal index was devised to measure the degree of sympathetic nervous system arousal. It was found that ground squirrels spent significantly larger amounts of time in fixed investigations when presented with live rattlesnakes or when primed with live rattlesnake encounters. Subsequent analyses will reveal the extent of nervousness, its effect on predation vigilance and ability to effectively discriminate between points of interest, and finally the patterns will be compared with that of Pacific gopher snakes, which are arguably less threatening to ground squirrel survival than their venomous counterparts.

Visit #29092 @Landels-Hill Big Creek Reserve

Approved

Under Project # 25572 | Research

Vigilance and snake predation responses in California Ground Squirrels

graduate_student - The University of Chicago

Reservation Members(s)

Rey Ayon Jul 9 - 11, 2012 (3 days)
Rey Ayon Jul 9 - 11, 2012 (3 days)

Reserve Resources(s) | Create Invoice