I’ve had a few conversations in the last year (most recently, yesterday) about the size differences in Crotalus atrox and other species of rattlesnake. In Arizona, the largest rattlesnake I’ve seen was maybe a few inches past 4′ in length, with the majority of encountered adults being just over 3′. I’ve found 4 instances of atrox in New Mexico; the largest, in the South Eastern part of the sate, was perhaps a small bit larger than the biggest one I’ve found in Arizona. The same species 2 states away in Texas get much larger, with an average of 4.5-5′, and a record size of 6′ 8″.
Thoughts on the subject from fellow herpers usually assume food availability and competition is a primary factor in our mini-atrox. I was doing some reading today on the topic and found found some information on supplemented food effecting growth rates (and other factors) in atrox. Although it does not infer discuss food availability in Texas versus Arizona, it does show that this is a factor that can directly result in larger or smaller animals. Interesting reading for anyone interested in the subject.
Taylor E.N, Malawy M.A., Browning D.M., Lemar S.V. & DeNardo D.F. (2005) Effects of food supplementation on the physiological ecology of female Western diamond-backed rattlesnakes (Crotalus atrox). Oecologia, 144, 206-213 (added by: Showler D.A. 2006).