I was on a deck with a large green space primarily with Douglas firs and oaks. A stellar's Jay flew into the neighbor's cedar tree approximately 50 feet tall 20 feet wide. The J proceeded to make exceedingly agitated calls at about a cadence of one a second for several minutes. The birds in the green space swarmed to the cedar and flew into it. I saw at least six Anna's Hummingbirds, a dozen or so chickadees, some Bush tits, some golden-crowned kinglets, a couple of towhees, maybe 10 or so juncos, the only bird that is in the screen space that I didn't see flying into it was a brown creeper. I imagine the great horned owl wasn't too impressed. For another two minutes or so the J continue the calls and all the birds were just flying around in a panic. There are Cooper's hawks I've seen here on several occasions including one about an hour earlier. The J flew to another tree called for another minute and then left and then slowly the other bird went back home. Any ideas what was going on here? Thanks David