Budgie Vision (3)

Magnetic Field

Migratory birds use the Earth's magnetic field for orientation. Some studies have suggested that the magnetic field is light dependant and birds are able to "see" it. During their migration through Australia, budgerigars are able to fly miles and miles in the correct direction, as they always seem to go "straight" to a waterhole or a food source. Budgerigars are probably able to see the magnetic field as well, but this has not been proven yet. Or do they use another technique we don't know about?

Image © cairns.ru

Edge detection

A lot of scientific effort has been devoted to studying how migratory birds navigate over long distances, but relatively little is known about how birds detect edges and avoid obstacles during landing.
A study in Australia has has investigated landing in budgerigars, by training them to fly from a perch to a feeder, and video-filming their landings.  

Image © greencheek on Deviantart

Description of the experiment:

"The feeder was placed on a grey disc that produced a contrasting edge against a uniformly blue background. We found that the budgies tended to land at the edge of the disc and walk to the feeder, even though the feeder was in the middle of the disc. This suggests that the birds were using the visual contrast at the boundary of the disc to target their landings.

When the grey level of the disc was varied systematically, whilst keeping the blue background constant, there was one intermediate grey level at which the budgerigar's preference for the disc boundary disappeared. The budgerigars then landed randomly all over the test surface. Even though this disc is (for humans) clearly distinguishable from the blue background, it offers very little contrast against the background, in the red and green regions of the spectrum.

In short:

Budgies rely on visual features in the environment, such as contrasting edges, to determine where they will land. Colours don't play a big part in this. The key to a successful landing is a clear contrast between the boundary (the edge) and the rest of the landing platform. That is how they do it! If the contrast is unclear, budgies may detect too many "edges" and not immediately find a perfect landing spot.

Copyright Bhagavatula P, Claudianos C, Ibbotson M, Srinivasan M (2009). "Edge Detection in Landing Budgerigars (Melopsittacus undulatus)"