I heard a big commotion of crows and I thought I heard a hawk retort. Uh oh they’re at it again. I moved to where I could get a better view. High in a tree, a hawk – I think it was a juvenile red tailed hawk – was under siege. Several crows took turns moving in as close as they dared, with loud scolding calls.
At one point I noticed that one crow was pulling lichen off of the tree branches in clumps and holding it in its mouth. It would then move in toward the hawk, as if brandishing the lichen. If the crow got too close the hawk would raise its wings defiantly.
Here you can see the crow (partially obscured by a branch) pulling some lichen off the branch.
In this photo, the same crow is flying away. Notice he still has the lichen in his beak. One by one all the crows flew off.