I’ve been surprised to learn how many people don’t know what these are.  They are the big showy flowers of the Tulip Tree, aka Tulip Poplar, or Yellow Poplar.

The trees are blooming now, but the flowers only tend to show up on parts of the tree with access to direct sunlight.  So unless you have a big leafy poplar at the edge of a clearing (not common), all the flowers are high in the canopy, and you don’t see them until wind breaks them loose or the spent petals break off and come down one by one.