Hummingbirds are one of nature’s most agile fliers. They can fly 50 kilometers per hour and stop on a dime to maneuver through dense vegetation. To do so, their vision must accommodate what their wings can deliver.
The most important facet of flying fast is judging distance. Insects and mammals process distance by how quickly an object moves past their field of vision: a technique termed image velocity.
Birds take a different tack. They rely on specific object sizes to determine distance, especially vertical size. This approach demands greater mental processing than image velocity, as it involves rapid point-to-point comparisons in real-time. Such precision is essential, as birds cannot survive collisions at relative speeds that would only stun insects.
Birds sense altitude in the same way that flying insects do, using image velocity in the vertical axis. Thus, avian vision processing takes 2 different algorithmic approaches for flight navigation. This is a most impressive exhibition of mental virtuosity, especially in tiny hummingbirds. Hummingbirds also have as good an episodic memory as any animal, including corvids. (Human episodic memory is pathetic compared to that of birds.)
To accommodate the cognitive workload, hummingbirds have the largest relative brain of all birds: 4.2% of total body weight. (Though hummingbirds have relatively large avian brains, their cranial real estate is still far too meager to explain their cognitive acumen as a purely physical phenomenon.) Hummingbirds also have (relatively) the biggest hearts and most powerful breast muscles, which take 30% of total body weight.