Not sure if this is the right place to post, but was watching some killdeer the other day (I had a very long lens and so wasn't close at all) and the killdeer would run, trill and do a fan tail. When I got back, I did some googling and found that some people say it is a courtship ritual (not sure if female or male does it) while others said it was to warn you not to step on them? Anyone know more about it? The courtship data goes back to posts in the 1920s by Theed Pearse and Aretas Sanders (cited by Townsend in an article in the Smithsonian). This is a link to the behavior:
https://www.flickr.com/photos/60519499@N00/52172020533/in/dateposted-public/