The researchers studied the color vision of Degus using electroretinograms and found that the visible spectrum for these animals extends into the UV range. To find an answer to the question of the benefits of this UV-abilities, they examined the natural environment of the animals for UV sources. The plants used as food by the animals only reflected low levels of UV, as well as earth, sand and stones. However, the researchers found what they were looking for in the fragrance brands with which Degus mark their surroundings.
In Degu colonies, commonly used main paths pass through the grounds and to the sand chairs. These communal facilities are extensively marked with urine and feces, partly for their own orientation, partly for delineating the territory against neighboring colonies.
The measurements showed that fresh Degu urine reflects the UV components of the light much more strongly than the longer-wave components. In contrast, aged, dried urine mainly reflects the longer wavelengths and very little UV. Thanks to their UV-sensitive eyes, Degus is able to differentiate between fresh and older urine marks visually, and not only by their odor intensity. So you can see where a conspecific recently walked and where the current hot spots are. display
Since odor signals are scattered by air movements and therefore do not represent very precise placemarks, the visual location of urine marks would provide a significant gain in orientation accuracy. Under this evolutionary pressure, rodents could have preserved their UV-abilities.MPG