Rain makes Bugs. Bugs are protein and Pheasant Chicks need protein to thrive.
I'm sure he understands that, and wasn't why he asked the question but rather that rain-soaked newly hatched chicks might not get to take advantage of the insect bloom. Just as I'm sure you understood what he's pointing out.
Is mid-June when hatching peaks in the pheasant belt? At what age can chicks tolerate being wet?