It's not unusual to see red-winged blackbirds

 

It *is* unusual to see this many red-winged blackbirds all together.

 

It’s a winter thing.  They move here to the south and bunch up.

 

The swarm is like a school of fish on a tropical reef.  They ebb, flow, and swirl in unison.

 

They make the impression that if you could stick your arm out into the flock, they would open up a space, and when you withdrew your arm, the space would close behind.

 

Perfectly fluid.