The thermal background determines how the infrared and visual systems interact in pit vipers

Area of Science:

• Ethology
• Sensory Biology
• Thermoregulation

Background:

• Pit vipers utilize thermal infrared (IR) sensing as a supplementary sensory system.
• The IR system is hypothesized to function as an alternative imaging system in low-light conditions.
• Optimal IR imaging is theorized for homoiothermic targets against cold backgrounds.

Purpose of the Study:

• To investigate pit viper prey discrimination and striking behavior under varying thermal background conditions.
• To evaluate the pit viper's thermal IR sensing system's performance relative to visual input.
• To test the hypothesis of IR system's 'brightness constancy' computation.

Main Methods:

• Experiments conducted on the pit viper species *Gloydius brevicaudus*.
• Utilized a modified predation cage with controlled, differential background temperatures (26°C vs. 33°C or 40°C).
• Sensory systems (eyes, pit organs, or both) were occluded to isolate the function of the IR system.

Main Results:

• When vision was occluded, snakes preferentially struck prey against a cooler background (26°C) compared to a similar temperature background (33°C).
• No significant preference was observed between 26°C and 40°C backgrounds when vision was blocked.
• Increased strike failures occurred when the pit organs were occluded, particularly against warmer backgrounds.

Conclusions:

• The pit viper IR system exhibits 'brightness constancy,' adjusting for target-background temperature differences.
• The IR system's efficacy in prey localization is diminished when the background temperature exceeds the target's temperature.
• Thermal IR sensing is crucial for pit viper predation, especially in scenarios with temperature contrasts.