Was antelope hunting near Casper around the 20th of September one year. The whole time was windy and cool (the day I shot mine was 38). Never saw a rattler. Crawled on my belly through sage brush about 20 yards to get in position for mine. I was talking to my BIL over the holidays and he had gone either a week earlier or later, and the weather was in the 70's or 80's. He said they were surrounded by rattlesnakes.
Long story short, I'd be real cautious in August.
