This past week in lecture we discussed the science behind animal vision. Specifically we looked at the different parts of the eye and saw the role that each plays in animal vision. It is also important to note that certain parts of the eye, such as the lens, are different structurally for different animals. These variations in structure ultimately lead to the variations in the type of vision used by different animal species. The researchers in this particular article looked at the different types of vision used by various bird species.

The article starts off by discussing the challenges involved with color vision. The main use of color vision is to help animals identify objects in environments where the light is changing. However one problem associated with color vision is longitudinal chromatic aberration (LCA). Basically this refers to the fact that light of short wavelengths is refracted more strongly than light from long wavelengths, and this causes problems in focusing which can be difficult to correct. Apparently one way animals deal with LCA is through the use of multifocal optical systems. In this system, the lens has different zones of various levels of refracting ability and these zones focus on narrow bands of light. Animals that have eyes with short focal lengths will gain the most from the use of multifocal optical systems. One problem for multifocal optical systems is the presence of circular pupils. It is known that all birds have circular pupils which are usually associated with a monofocal optical system, however the researchers wanted to know if birds used multifocal optical systems.

In order to conduct their research, various species of birds were captured and examined at the Falsterbo Bird Observatory in Sweden. A total of 45 bird species were studied from 12 different orders. A few of the species were the bald eagle, great horned owl, blue tit, emu, ostrich, grey parrot, and emperor penguin. The first order of business was to determine if the bird had a monofocal optical system or a multifocal optical system. The monofocal systems are detected by the presence of a smooth fundus reflex while multifocal optical systems are detected by the presence of a fundus reflex which has ring like structures. The researchers also measured the size of the pupils to see how wide they could open.

The research showed that bird species can have either monofocal or multifocal operating systems with multifocal optical systems being more common. Of the 45 species, 29 had multifocal optical systems and 5 had monofocal optical systems. The researchers weren’t able to tell which optical system was used in the remaining 11 species. In terms of the pupils, all the birds except the emperor penguins and the homing pigeons had circular pupils. The emperor penguins have diamond shaped pupils while the homing pigeons have oval shaped pupils. Of the birds studied the great horned owl had the largest pupil diameter of 15 mm while the hedge accentor had the smallest pupil diameter of 1.5 mm. One trend that I noticed was that the owls in general tended to have the largest pupil diameters, this is probably due to the fact that they are nocturnal. If I had to guess the large pupils help them to take in more light at night, thus giving them the ability to see better at night.

In conclusion, the presence of multifocal operating systems seems to be fairly common in birds. It is believed that they use this type of system because they are highly sensitive to UV light or because they have a short depth of focus.