I grew up in a place where making maple syrup was an integral part of the early spring. Here in Western New York they also make syrup, and the boiling sap is a unique smell easy to recognize in the air.
For sugar maple trees, there doesn't seem to be a more active time than spring. The buds come out on the trees in extremely adverse weather conditions, and then, one day, it's warm enough for long enough that the sap starts to run. The buds change color overnight, and the tapping begins.
Here in Buffalo, it was in the 50's for the last three days. Today, in the mid-thirties. The sap running doesn't mean winter is over, it's just a really good promise that it will end eventually. And those first few batches of fresh, sweet maple syrup are definitely the taste of spring to me. If you haven't been to a "Sugar house", the place where syrup is made, call around. Go to a sugar party. Happy spring!