A fairy ring has shown up in my yard for the past two years. This one is strangely centered on my bird feeder. Articles on fairy rings suggest that sometimes rabbits are the cause of the rings. In this case my theory is that the bird droppings are doing the same thing that the rabbit droppings do.
There are also several smaller mushrooms behind the feeder that are hard to see in this picture. Also hard to see is that the grass is greener and taller in the ring. Click on the picture for a larger image.