Thermal modeling of snake infrared reception: Evidence for limited detection range

For more than 40 years, information has circulated with regard to the sensi tivity of infrared pit organs in both bold and crotaline snakes (pythons an d pit vipers, respectively). The most often quoted sensitivity is 0.003 deg reesC and this value is based on the work of Bullock and co-workers (1956). Missing from previous work was a quantitative model of radiation transfer that would report sensitivity not in terms of degrees Celsius, but rather s ensing distance. Since prey detection is often cited as the function of the infrared pit organ, quantification of this sensing distance seemed to be a n important value that was missing from the literature. In this paper, we m odel the radiation transfer process from a 37 degreesC object, i.e. warm-bl ooded prey, to an infrared pit organ. The model tries to answer a very basi c question-at what distance does the thermal signature of a 37 degreesC obj ect blend into the background for a non-imaging biological infrared sensor? The output of the model, the sensing distance, is of particular interest i n comparing biological infrared sensors to current semiconductor-based infr ared (IR) detectors-largely because of inappropriate comparisons between th e temperature sensitivity of IR snake reception and imaging IR cameras. The purpose of the presented work to make more appropriate comparisons, i.e. s ensing distance. This sensing distance output indicates an extremely short detection distance (<5 cm)-contradictory to what is observed experimentally . This dichotomy raises further questions regarding how the biological syst em amplifies this weak signal. <(c)> 2001 Academic Press.