Understanding the Ability of Birds to See Underwater Prey

Image obtained through the air-water interface is determined by light refraction. This affects many parameters such as image apparent shape, position, motion, contour, contrast and more. Birds of many species, such as ospreys, kingfishers, and herons, capture fish after observing and aiming from the air and can compensate for these effects and successfully strike their prey.
In this project we researched the geometrical distortions caused by refraction of light rays through the air-water interface and expanded the process to a sea surface with waves. Afterwards, we defined the type of distortion caused by the water surface and proposed a way to measure said distortion. Finally, we have combined the tools developed in the first part of the project with drone video recordings of birds hunting underwater prey, to determine if the bird can identify the underwater prey under certain water conditions.
These steps were conducted using physics describing light rays passing through different media, various image-processing techniques and recordings showing the behavior of birds while hunting.
During the project, we created a simulation tool that can synthesize images distorted by a water surface. The simulator provides the ability to define the position of the prey, bird, and the water surface conditions, and then measure the distortions in the obtained distorted images. Using this simulator, we conducted several experiments to understand under which distortions an underwater prey could be identified, and we characterized the distortion the birds cope with.

Birds hunting underwater pray

Understanding the Ability of Birds to See Underwater Prey