Hummingbirds are the tiniest birds in the animal kingdom. They are also some of the fastest, reaching flight speeds of up to 54 kilometers an hour. Their high flight speed means that they need to be able to process visual information quickly to avoid collisions. A study just published in the Proceedings of the National Academy of Sciences journal provides new insight into how hummingbirds navigate their environment at high speeds.
Previous studies had already shown how insects determine flight speeds and how close they are to objects. Insects, such as bees, process distance by tracking how quickly objects pass through their field of vision. This is the same way humans process speed and object distances while driving. Objects that pass by quickly are nearby but a mountain in the distance may take more time to drive past, telling our brain that it’s farther away.
The researchers set up a tunnel for the hummingbirds to fly through. The chamber was set up so that there was a perch on one side and a cup of sugar water on the other side. Hummingbirds seek out sugary substances constantly since they have one of the fastest metabolisms of any animal. The research team was able to manipulate the images and patterns on the tunnel wall in order to study how the little birds navigated their environment.
The hummingbirds didn’t process distance the same way as humans and insects. Rather than track how fast an object is passing by, the birds used the size of the objects. If an object started to get bigger, the hummingbirds assumed that it was getting closer. As an object got smaller, the birds knew that they were moving away from it. The hummingbirds also used a technique called image velocity to adjust their flight altitude. If the researchers changed the chamber patterns to simulate going up or down, the birds changed their flight.
Hummingbirds have very fast flight speeds. Their speed combined with fragility makes it critical that they’re able to properly gauge distance and avoid collisions. Researchers have now shown that they navigate using image size and image velocity. This is unlike both insects and humans, showing that birds may have a unique way of navigating while in flight.
Roslyn Dakin et al. Visual guidance of forward flight in hummingbirds reveals control based on image features instead of pattern velocity. PNAS (2016).