Thermoregulation is the pits: use of thermal radiation for retreat site selection by rattlesnakes

Abstract

Pitvipers (Viperidae: Crotalinae) possess unique sensory organs, the facial pits, capable of sensing subtle fluctuations in thermal radiation. Prey acquisition has long been regarded as the sole function of the facial pits. However, the ability to sense thermal radiation could also direct thermoregulatory behavior by remotely sensing nearby surface temperatures. Using a series of behavioral arenas of varying spatial complexity and ecological relevance, we surveyed the ability of the western diamondback rattlesnake Crotalus atrox to direct successful thermoregulatory movements with either functional or disabled facial pits. We found that western diamondback rattlesnakes could base thermoregulatory decisions on thermal radiation cues when their pits were functional, but not when blocked. Our results indicate that the facial pit is part of a generalized sense, and suggest thermoregulation as an alternative hypothesis to prey acquisition for the origin of facial pits.

Analytical methods for the geometric optics of thermal vision illustrated with four species of pitvipers

“…Behaviorally, the facial pit appears to function as an 'eye' because it can compensate for visual deprivation (Kardong and Berkhoudt, 1999;Kardong and Mackessy, 1991). It aids prey acquisition (Bullock and Diecke, 1956;Clarke et al, 1996;de Cock Buning, 1983;Kardong, 1986;Noble and Schmidt, 1937) and thermoregulation (Krochmal and Bakken, 2003;Krochmal et al, 2004). Proposed but untested functions include situational awareness and predator detection (Bullock and Barrett, 1968;Greene, 1992;Sexton et al, 1992).…”

Directional sensitivity in the thermal response of the facial pit in western diamondback rattlesnakes (Crotalus atrox)

“…Kardong and Mackessy, 1991; Van Dyke and Grace, 2010) and when locating thermal refugia (Krochmal and Bakken, 2003). One of the hindrances to a deeper appreciation of the functional role of the pit organ is uncertainty regarding the thermal and directional sensitivity of the system, i.e.…”

Respiratory cooling in rattlesnakes

“…Pit organs are thermoreceptive organs derived from tactile receptors, and, like other sensory organs, must be maintained within a narrow temperature range (Molenaar, 1992). Because these receptors are critical during activities ranging from prey capture to microhabitat selection (Krochmal and Bakken, 2003), understanding the thermal environment in which they operate is a primary goal of this study.…”