Hi Brian,

Your guess about the Osprey display was right.

Brian Cassell said,
"It (he?) was high overhead vocalizing and flying what I assume was a courtship display (vertical undulations without any significant horizontal change in position)." 

It was what I like to call the "J" display.  This courtship display by the male looks to me as if he is sky writing the letter J. 
The Nanjemoy Creek Ospreys returned on March 7 but only started displaying on Friday March 18.

Naturally,
Mike Callahan
Nanjemoy, Charles County, Maryland