The Happy Hour For Birds?

My neighbor has a tall cherry tree near the fence separating our lots.  I have never seen it bear berries before, but this fall the tall canopy of the tree has been full of giant red shiny globes, delicious even from a distance.  It still is fairly full of those berries, and thereby hangs a tale.

Very early one morning I woke up to a tremendous cacophony of sounds, birds speaking to each other in full voice in a hundred different languages, at different frequencies and levels of loudness.  Beautiful it was not, a nature's symphony it was not.

I looked out from a second floor window and saw birds everywhere.  About forty starlings pecking at the so-called driveway (which is not abnormal), three or four blue jays leaning weirdly on top of the roof, a couple of morning doves playing bomber planes at the ground and at each other, and ten or so robins lying in the grass.  And when I say "lying in the grass," I mean it.  When I made a fearsome noise, a couple of the robins managed to fly away, the others turned glazed eyes at me and that was it.

I opened the window and stuck my head out and got bombarded by a pair of small birds.  They flew so close to my face that I felt the air their wings moved in my hair.

All this was a little troubling.   Suddenly I heard a noise from another second floor window, one which has a narrow screen for ventilation at the bottom.  A blue jay was busily trying to tear that screen into small pieces.  As I approached the window, from inside the house, the jay looked at me, scornfully, and resumed its wrecking work.

After an hour or so the happy time was over and things returned to normal (well, normal for the Snakepit Inc.).  But the same show was repeated at slightly lower attendance rates for about a week.

What's going on here?  Are the berries in the cherry tree fermented, thus offering migrating (and non-migrating) birds a nice alcoholic bar?  A birds' happy hour?

I don't think any birds were harmed in making this spectacle.