This falcon-cam view as the predator hunts a crow is incredible — but just as incredible is the old sailing illusion it's using to do so.

New Scientist reports on research from scientists at Haverford College that tracks the hunting movement of peregrine falcons through the use of the (highly enjoyable) falcon-cam. The researchers had predicted that the hawks would follow a spiral pattern that had been predicted using mathematical models. So, how did the models do?

The falcons did not behave as predicted. Instead, they fixed a potential victim in their field of view using a method commonly used by sailors to avoid collisions, called constant bearing. This meant they were always flying towards the prey's future location, ready to intercept them.

Yep, falcons are hunting crows using the old sailor's illusion of constant bearing decreasing range (CBDR), where, although the objects are rapidly moving closer, they maintain the same course which tricks the eye into thinking that the distance hasn't yet been closed.

In nautical terms, this can often mean a collision between two boats. In ornithological terms, it's bad news for the crow.