Are these both grammatically correct? "ON September 23 through 26, 2013, birds were observed on the lake." or "FROM September 23 through 26, 2013, birds were observed on the lake."
They are correct, with different implications. The first sentence, using 'on', implies that the event (birds being seen) occurred individually on each of those days. The second, using 'from', implies that the seeing of birds was continuous through the entire duration.
A better pair of examples: "On September 23rd through the 26th, we will be going out to lunch." "From September 23rd through the 26th, we will be on vacation."
That said, the implication is by no means definitive; 'from' could just as well be used in the first example and still be correct.