Behavioural examination of the infrared sensitivity of ball pythons


Guido Westhoff, Institute of Zoology, Department of Comparative Neurophysiology, University of Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany.
Tel: +49 228 73 54 76;
Fax: +49 228 73 54 58


The ability to detect infrared (IR) radiation is a characteristic trait in boids and pitvipers. These snakes possess highly sensitive IR receptors, which enable them to perceive IR sources and assess their direction and distance independently of visual cues. Electrophysiological studies have been conducted to determine IR detection thresholds in boids and pitvipers. This, however, is the first behavioural study that focuses on the detection threshold of a boid snake to IR stimuli. Blindfolded ball pythons Python regius were exposed to a moving IR stimulus of constant size and temperature at various distances (10–100 cm). Distinct behavioural changes during stimulus presentation (S-form posture, freeze and fix, follow and fix) allowed quantification of the behavioural responses. The threshold to elicit behavioural responses was used to assess the IR detection threshold. The results revealed that P. regius can detect a moving IR stimulus resembling a mouse in temperature and size up to a distance of 30 cm, which corresponds to an irradiance contrast of 38.83 × 10−6 W cm−2. This irradiance contrast detection threshold value is about one-third lower (reveals a 1.5 times higher sensitivity) than the results from earlier electrophysiological studies.