The chicks Alpha and Omega (which we formally observed for some months) used to do this in synch, and go completely nuts doin' it. It's not, I suggest, just 'a mating dance'. I think it's part that and part pure enthusiasm for life.
Note also that what the videos of spazzy dances don't snow is how running fits in. Emus will run huuuuuundreds of meters during a good spazzy dance. That is, they do the spazzy thang, then run wildly about, then stop for more spazzy-ing.
[Felicity is here this morning, dealing seriously with a female interloper.]