Robins and Thrashers laying around tree with wings fully extended?

[peacebird]

Very odd - groups of three (up to 8 birds) Robins and Thrashers both - lay on their bellies, facing the tree trunk and extend their wings and tail feathers fully....
After a few moments they scatter, then come back and do it again?

Why on earth are they doing this? It is the funniest thing....

 

[justusnak]

Sounds to me they are dust bathing, or sunning just like chickens do! Very interesting...birds are.