I've hunted western OK a few times. The first year I went, birds were everywhere. The day I left, in early April, it was 97 degrees, and they had an extremely dry and hot summer. Two years later, I went back, and didn't see a single adult tom in 3 days of hunting. A friend of mine quail hunts in the same area, and he said the quail hunting was horrible the same year it was so hot. He was told it was so hot and dry, that most eggs never even hatched, so I'm guessing that, yes, a severe drought can adversely effect the turkey population.