2 Dead Chicks: Dehydration?

[Salt and Light]

Temps are in the 70s. I don't use a thermometer, I go by behavior. Huddled up = more heat, spaced out and or panting = less heat. I check on them often and adjust according to conditions and behavior. Also, the 3 chicks that died did so at very different times. One was dead early this AM, another died a couple hours later and the last died a couple hours after that.

What is PVS