How do birds know how to avoid flying into things?
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How Birds Avoid Flying into Obstacles
Birds exhibit remarkable agility and precision in flight, allowing them to navigate complex environments and avoid collisions. This article synthesizes research findings on the strategies and mechanisms birds use to avoid flying into obstacles.
Collision Avoidance Strategies in Birds
Veering and Altitude Adjustment
Research on budgerigars has shown that birds employ simple yet effective strategies to avoid mid-air collisions. When faced with a head-on encounter, each bird tends to veer to its right and adjust its altitude relative to the other bird based on a preset preference. These strategies suggest that birds follow straightforward rules to prevent collisions, which could be applied to automated collision avoidance systems in aircraft.
Visual Guidance and Force Vectoring
Birds also use visually guided force vectoring to maneuver around obstacles. For example, Pacific parrotlets adjust their body pitch, stroke plane angle, and lift-to-drag ratios to navigate around obstructions. This involves redirecting forces with their legs and wings, allowing them to make controlled collisions with their target perches. This method highlights the importance of drag in avian maneuvering and provides insights into the evolution of flight.
Idiosyncratic Flight Paths
Budgerigars exhibit highly individualistic flight paths that they consistently follow, even when obstacles are introduced. They tend to stick to their preferred trajectories, making minimal deviations to avoid collisions. This behavior underscores the robustness of their flight paths and their tendency to pass obstacles by flying over them.
Visual Cues and Optic Flow
Image Features and Pattern Velocity
Hummingbirds use visual information to control their flight paths. Unlike insects, which regulate fore-aft image velocity, hummingbirds rely on the vertical size of features for lateral course control. They adjust their altitude based on the vertical motion of the horizontal plane, suggesting that birds monitor the vertical extent of features to avoid collisions.
Brightness Cues
Zebra finches use brightness cues to navigate through gaps. They are more likely to fly through tunnels with bright backgrounds and tend to exit towards the brighter side. This indicates that birds may pre-plan their flight trajectories based on visual contrast between foreground and background objects.
Optic Flow
Birds use optic flow cues to navigate narrow passages. By balancing the speeds of image motion experienced by their eyes, budgerigars can fly through narrow gaps without collisions. This strategy is similar to that used by flying insects, suggesting shared principles of visual guidance among diurnal flying animals.
Sensory Mechanisms and Evolution
Visual Signals
Larger bird species and colonial breeders often have more contrasting ventral wing patterns, which serve as visual signals to avoid collisions. These patterns are particularly important for species with lower maneuverability and those that frequently encounter other birds.
Anticipatory Maneuvers
Birds execute anticipatory maneuvers when flying through narrow apertures. They close their wings at a constant distance before the aperture, regardless of its width, and often fly higher to compensate for altitude loss. This behavior indicates that birds use optic flow to gauge distances and guide their maneuvers.
Conclusion
Birds employ a combination of simple rules, visual cues, and anticipatory maneuvers to avoid collisions during flight. These strategies are informed by visual information such as image features, brightness, and optic flow, allowing birds to navigate complex environments with precision. Understanding these mechanisms not only provides insights into avian behavior but also has potential applications in designing automated collision avoidance systems.
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