Abstract
Sensory information drives the ecology and behaviour of animals, and some animals are able to detect environmental cues unavailable to us. For example, rattlesnakes use infrared (IR) radiation to detect warm prey at night when visual cues are reduced. Until recently these sensory worlds have been inaccessible to human observers; now technology can allow us to “eavesdrop” on these species and understand how sensory perception drives ecology and behaviour. We used thermography and computer simulations to examine how prey-background temperature contrast and areas of temperature transitions influence the angular orientation of free-ranging rattlesnakes once they have selected an ambush site. We tracked free-ranging sidewinder rattlesnakes Crotalus cerastes to their selected ambush sites and recorded 360° near-ground thermographic panoramas from the centre of the ambush site. A computer simulation then moved a simulated prey item across the panorama and computed a contrast index for all directions. Rattlesnakes did not face ambush directions that offered stronger contrast than average, but they demonstrated a striking tendency to face directions with strong thermal transitions. Background transitions likely create a readily detected, rapidly changing stimulus when a prey animal passes. Quantifications of sensory environments like this one can boost our comprehension of how sensory function impacts the ecology, behaviour, and evolution of animals.
Highlights
The sensory systems of some animals allow them to sense environmental stimuli that are not detectable by other organisms
The combination of thermal contrast detection, phasic neural response, and low-resolution imaging means that strong contrast and sudden changes in the thermal scene may be more detected than low contrast and slow changes
Prior studies suggest that foraging pit vipers should select cool, homogenous background temperatures
Summary
The sensory systems of some animals allow them to sense environmental stimuli that are not detectable by other organisms These specialised sensory channels are often the foundation for ecological and behavioural specialisations and may be responsible for subsequent adaptive radiations. We are interested in how pit vipers might use IR sensing to select a strike direction once a general area of prey activity has been located. IR detection is used for behavioural thermoregulation[8,9] and to detect endothermic prey in the absence of light[10,11,12] Experiments show that this enhanced sensory ability allows pit vipers to be more effective predators of nocturnal rodents compared to similar non-IR sensing vipers[13]. Prey animals might be more detected against thermal backgrounds with temperature transitions, i.e. areas where the contrast between moving prey and background changes rapidly, such that the prey animal will “pop” into view when it moves across the transition
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