Perhaps he was as stupid as a turkey i.e. when it started raining he looked up to see what was hitting him in the head. As he stood there looking up with his mouth agape he inhaled enough water to overwhelm his normal pulmonary function. So,
he drownded.
I am not able to verify this information as it relates to the turkeys as it came from my children and they've been known to embellish factual events to the point of being absurdly plausible, yet highly unlikely.