How do birds and schools of fish seem to turn in unison? They appear to be connected to some sort of SONAR.?

Answer 1

It is discussed here: http://www.straightdope.com/mailbag/mflockswoop.html

"Research by Wayne Potts, published in the journal Nature in 1984, helped explain how flock movements are initiated and coordinated. Potts, through a frame-by-frame analysis of high-speed film of sandpiper flocks, found that any individual can initiate a flock movement, which then propagates through the flock in a wave radiating out from the initiation site....
...Once one of these waves began, Potts found that it spread through the flock far more rapidly than could be explained by the reaction times of individual birds. A bird's mean startle reaction time to a light flash as measured in the laboratory was 38 milliseconds, but maneuver waves spread through the flock between birds at a mean speed of less than 15 milliseconds. However, the first birds to respond to an initiator took 67 milliseconds to react. Potts proposed that birds farther away from the initiation site were able to see the wave approaching them, and could "get set" to respond before it actually reached them. He dubbed this the "chorus line hypothesis," in analogy to Rockettes at Radio City Music Hall who can see and anticipate an approaching high leg kick when it is still well down the line. Films of human chorus lines show that rehearsed maneuvers, initiated without warning, propagate down the line at less than 108 milliseconds, almost twice as fast as the human visual reaction time of 194 milliseconds."

Answer 2

School fish have a line running down their side which is sensitive to electrical impulses induced by movement of other fish near them. It causes them to react, and begin moving in a communal direction, very quickly.