Birds are known to have extraordinary color vision during the day. Among other things, this ability helps them to distinguish among the dazzling array of avian plumages. New research shows that birds' color vision vanishes at dusk.
For humans and horses, color vision ceases to work after dusk, at light intensities roughly corresponding to bright moonlight. However, the light threshold is not the same for all vertebrates. Geckos, for instance, can see colors at night. In the experiments performed by the Lund University Vision Group, the color vision of birds stopped working at light intensities corresponding to what prevails shortly after the sun goes down. Birds need between 5 and 20 times as much light as humans to see colors. Among all the vertebrates tested thus far, birds are the first to lose their color vision in the twilight, even though they are the vertebrates that probably see colors best of all in the daylight.This conclusion is interesting in its own right. I wonder if it might also have some application to other questions about bird behavior. During migration, birds fly at night, a task that requires both an aerodynamic body and special navigation skills. Conventional wisdom at the moment indicates that birds navigate using a combination of the Earth's magnetic field and the stars. Would lack of color vision have any bearing on navigation? Second, there remains the problem of birds colliding into windows and other man-made structures. Could this be caused in part by the lack of color vision in dark or dim lighting conditions? Perhaps this finding could inspire new ways to prevent such fatal collisions.
With these findings it is now possible to start to draw conclusions about how birds use their color vision at dawn and dusk. The findings also direct our focus to previous research about how important color is when it comes to eggs or begging baby birds in enclosed nests. Inside enclosed nests it is dark even when the sun is bright outside.
"Against the background of our new discoveries, we should now re-evaluate earlier research about how birds perceive the color of their eggs and their young in the nest," says Olle Lind.