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Fig. 7. Two situations relevant to pitviper biology present particularly strong
surface temperature contrasts. (A) A rodent burrow below a desert shrub at
high noon, scaled to an 80° view angle with the burrow 28 cm distant.
Conditions are warm but not extreme, with air temperature of 33°C and peak
ground temperatures near 50°C. (B–D) Pit membrane temperature
contrasts visualized using the indicated
i. The burrow could
be easily identified from a distance by a snake leaving the shade of a bush to
seek underground shelter. (E) An American cardinal Cardinalis
cardinalis viewed against a clear sky, scaled to an 80° view angle
with the cardinal 31 cm distant. Note that the thermal imager does not record
radiant sky temperature properly, and so the sky has been rescaled to a
radiant temperature of 5°C on the basis of Swinbank's formula
(Swinbank, 1963). (F–H)
Pit membrane temperature contrasts visualized using the
i
indicated for that row. The temperature contrast on the pit membrane in
B–D and F–H are indicated by color steps of 0.001°C.