As seen in the previous section, eye placement can affect the size of each of the portions of the visual fields (binocular field, lateral field, blind area). Scientists classify avian visual fields in three main types: 1, 2, and 3.

Visual field type 1: typical of species like the starling, which has binocular and blind areas of intermediate sizes. Given the lateral placement of the eyes, these species are able to have larger binocular fields than owls. Species with this type of visual field can see the tip of their beaks, which allows them to manipulate food items (imagine a starling trying to eat a squirming worm).

Visual field type 2: typical of species like the mallard, which has small binocular and blind areas, and large lateral areas due to the largely peripheral placement of the eyes. In some species, the large size of the blind areas would allow the animals to see almost around its whole head (large visual field).  These species generally do not manipulate food items with their beaks (e.g., they are filter feeders); so they do not require a large binocular area.

Visual field type 3: typical of species like the owl, which has large binocular and blind areas due to the frontal placement of the eyes. This type of visual field is the one with the highest similarity to that of humans in terms of the size of the blind area. These species generally grab food items with their feet by using their binocular field while approaching the prey. 

Imagine that these three species (owl, starling, mallard) are standing head-up in the middle of a city park. What would be the extent of what they can see around their heads based on the types of visual fields explained above?

To answer this question, imagine we take pictures of what these birds can see at the plane of their beaks as if they were windows and paste them on a piece of paper. Find out the answer by downloading this file.

As you can see, there are substantial differences in the size of these windows, being largest in the species with the most peripherally placed eyes (mallard), and smallest in the species with the most frontally placed eyes (owl).

For the small ones, you can download the following coloring page showing the main difference between the visual fields of two species with type 1 and type 3 visual fields.

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