http://www.theguardian.com/science/video/2014/jan/16/head-mounted-cameras-falcons-killer-strategy-video

Footage from cameras strapped to falcons' heads and backs reveals
how they close in on crows without alerting them. Rather than head straight for
the prey, the falcons keep the birds in a fixed position to one side. The
strategy exploits an effect called 'motion camouflage' where the predator does
not seem to be moving from the point of view of the prey. The only clue is the
gradual increase in its size.

Thanks to Adam Palmer.