Fleur de Lis

On a lovely hushed walk through uninhabited woods, I found these fleur de lis shaped seeds, and was quite intrigued. They also look a little like tiny birds.  

They were scattered across my path in a line from one side of the road to the other, like this

I wonder if the grader that plowed this route scraped the branches above it, loosening the seeds?

My investigations online seem to indicate they are yellow birch seeds, described in The Berkshire Edge as looking like soaring birds or tiny airplanes.