Function
The function of the optic lobe is to receive and intrepret the information provided to the lobe by the optic nerve. There are two optic lobes in the brain, and they are located on each side. Each optic nerve is attached to one optic lobe. The lobes then in turn send messages to other areas of the brain such as the thalamus, brain stem and motor nerves which then can react appropriately if necessary.
Size
In general, optic lobes in birds are very large compared to other vertebrates. This enlargement of the lobes shows that vision plays a significant role in the survival of birds. However, some birds, such as the kiwi (a nocturnal, flightless bird), have much smaller optic lobes compared to olfactory bulbs. The kiwi uses the sense of smell over the use of vision to locate food.
The Process
Visual stimuli enter through the lens and are projected onto the retina. The rod and cone cells present in the retina "see" the image and transmit a signal through the optic nerve to the optic lobes. The optic lobes then interpret the image and determine what is being seen. The lobes will then send messages to other areas of the brain if action is necessary. For example, if a threat is seen, the optic lobes will send a message to trigger a flight response.
Bird Sight
According to the Poultry Hub website, birds see in colors just like humans do. The structure of the eye is similar except for the additional pectin present in bird eyes. The function of the pectin is to be able to maintain sharp focus even after staring at a given object for long periods of time.