Ground squirrels use an infrared signal to deter rattlesnake predation
- *Animal Behavior Graduate Group and
- Departments of ‡Psychology and
- §Mechanical and Aeronautical Engineering, University of California, One Shields Avenue, Davis, CA 95616
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Edited by Peter Marler, University of California, Davis, CA, and approved July 19, 2007 (received for review March 20, 2007)
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Fig. 1.Mean surface temperatures in each of the testing conditions across the six measured regions of the subjects' head, body and tail. Testing conditions are coded as, ■, rattlesnake; ▵, gopher snake; ♦, conspecific; ○, baseline. Squirrels increased emission of tail-infrared radiation over baseline and control levels during rattlesnake trials but not during gopher snake trials. *, P < 0.01 compared with conspecific and gopher snake; †, P < 0.01 compared with baseline, conspecific, and gopher snake. All points represent means ± SEMs, and planned comparisons were performed by using paired samples t tests. Points are connected for ease of reading and do not imply continuous measurement.
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Fig. 2.Infrared video frames of a squirrel interacting with a rattlesnake (A) and a gopher snake (B) during experimental trials. Pixel color corresponds to object surface temperature. Note that the tail regions of the squirrel are considerably warmer than the background during the rattlesnake trial but not the gopher snake trial. Stimulus cage partially obstructs the squirrel's head in B.
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Fig. 3.Rattlesnake responses to the robotic squirrel models. (A) One of the robotic squirrels used for playbacks of tail flagging with (infrared) and without (control) an infrared component. Proportion of time intervals spent by the rattlesnake subjects oriented toward the robotic model (B), moving in the testing chamber (C), in an elongated posture (D), in a coiled posture (E), and in a cocked-to-strike posture (F). Bars represent means ± SEMs. *, P < 0.05 by a Wilcoxon signed-ranks test compared with all other conditions.
Footnotes
- †To whom correspondence should be addressed. E-mail: asrundus{at}ucdavis.edu
- © 2007 by The National Academy of Sciences of the USA
