Strike a pose

When I replenish the feeding station, a crowd gently gathers and it's the resident Robins that prefer to be at the front of the queue. Normally they will just perch and watch. Though sometimes they show their in-patience by fluttering their wings or giving a little hop.

Today was a little different. Two of them decided to adopt this strange pose and advance towards each other with their tail feathers at 90 degrees. Not sure if it was an act of aggression or some kind of courtship dance. Does anyone out there have any idea?