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Description
Much research in behavioral ecology has focused on trying to understand how the environment influences animal foraging behavior. These environmental influences may manifest themselves through both abiotic and biotic factors. For my thesis research, I examined how certain abiotic and biotic factors influence free-ranging rattlesnake foraging behavior. While foraging, rattlesnakes will search for ambush sites and wait for hours, sometimes days, for unsuspecting prey to come within striking distance. However, we know virtually nothing about the behavior rattlesnakes' exhibit during this waiting period. In chapter 1, I examined how an abiotic factor, natural light availability, influences rattlesnake behavior during this waiting period. I used a combination of radio telemetry and portable video surveillance cameras to quantify the behaviors exhibited by rattlesnakes while waiting for prey during both day and night periods. The two most common behaviors I observed were chemosensory probes, a behavior I describe in detail for the first time, and mouth gapes. The frequency of these behaviors changed from day to night periods. The rate of chemosensory probing increased by 82% from day to night. Likewise, the percentage of hours with one or more mouth gapes increased by 35% from day to night periods. Nearly half of all mouth gapes were followed immediately with a chemosensory probe, suggesting that mouth gaping also serves a chemosensory function in this context. Our results suggest that chemical cues play an increasingly important role in mediating rattlesnake foraging behavior at night, a pattern that may be true for many sit-and-wait predators that ambush prey opportunistically throughout the day and night. In chapter 2, I examined how a biotic factor, ground squirrels approaching and tail-flagging toward rattlesnakes, influences rattlesnakes foraging behavior. I conducted this study using manned and unmanned video cameras to record behaviors of radio-tagged, free-ranging rattlesnakes foraging in ground squirrel colonies. I found that squirrel tail-flags deter snake predation on two different time scales. At the time of the interaction, snakes did not strike at tail-flagging squirrels unless they approached too close -- about 1/3 of the distance of their typical strike range. This is likely because tail-flagging is reliably associated with squirrel vigilance and their readiness to dodge a snake strike. Tail-flagging also influenced subsequent behaviors of rattlesnakes. Tail-flagging by adult squirrels increased the probability that snakes would leave the area; however, tail-flagging from pups did not cause snakes to leave the area. Snakes did not respond to tail-flagging interactions with pups because they actually experienced an increased probability of striking a squirrel in the area. These differences in snake responses are likely shaped by the differential effects of pup and adult tail-flagging on nearby squirrels, as well as pups being associated with high prey density areas. Taken together, my thesis research has shed light on how certain abiotic and biotic factors influence rattlesnake foraging behavior, a group of predators we know little about.
