Beginning with my first visit to the study site on 3 January, I began measuring ground temperatures with an infrared thermometer, rather than the mercury-filled glass thermometer I have used for a long time. The infrared thermometer is much faster (just point and pull the trigger) and actually gets the surface temperature, rather than the air just above the surface, since conduction with the ground has the biggest influence on the snakes’ body temperature unless they’re in direct sun.
3 January was also the coldest day I have experienced at this study site so far, with the shade surface temp at 4C (39F) at 10 AM. The body temps of males # 35, 38, and 40 (all in the same refuge together) were 45F, 50F, and 48F, respectively. Female #39, in the same refuge as the boys but several feet away, was 52F. Female #41, spending the winter by herself (as far as I know) in ground squirrel tunnels under a large live oak, was 41F.
On 2 February at 2:13 PM, I came across another small unmarked rattlesnake basking in diffuse sun (high thin overcast) at the refuge with CRORs 35, 38, 39, and 40. This snake fled into the refuge when I approached and was not captured.
Also on 2 Feb, female #41 had moved about 20 feet from among the live oak roots to under an old log she had used briefly last summer but she was out of sight either in or under it.