You round a corner onto a city street, and you realize you need to drive between a bunch of trucks parked on the right and the busy traffic lane on the left. So what do you do? You slow down and drive carefully, adjusting your speed as you go.
Research at the Queensland Brain Institute (QBI) has shown that birds will interrupt their wing beats to raise their wings or tuck them against their bodies when flying through a narrow gap, reducing their width very precisely. (Don't you wish you car could do that?) But it also shows that they don't slow down while making these adjustments. So how do they manage to make them at the right time?
Researchers QBI's Visual and Sensory Neuroscience Laboratory analyzed the flight of budgerigars—parakeets (Melopsittacus undulatus)—as they flew through narrow gaps of varying width. Dr. Ingo Schiffner and Hong Vo filmed the birds, then did 3D reconstruction of their flight, which revealed that the birds seemed to plan ahead—1.4 meters ahead, in fact. (That's about 4.6 feet). And they even knew to fly a little higher because they'd drop later when interrupting their wingbeats. In other words, the parakeets made flight decisions well in advance of the obstacles.
Even though the birds did some fancy flying, they didn't slow down. In another study, when parakeets flew through gradually tapering tunnels, they switched between what looked like two pre-set speeds, which Dr. Schiffner refers to as "low maneuvering" and "high cruising," bearing out the finding that they seemed to plan ahead, seeing and estimating the width of the tunnel.
This research might be especially helpful as we (humans, that is) design and build aircraft capable of unmanned flight. Current guidance systems are based on research in insects, but birds seem to have a different set of capabilities.