Smell and taste are poorly developed in birds. However, touch, hearing and vision are very important senses. Sensory organs are proprioceptive and tactile corpuscles. Together with vision, tactile corpuscules are used for selecting food. These are located on the border and sides of the beak, as well as within the oral cavity. They perceive size, shape, toughness and superficial characteristics of food.
Feathers prevent the skin from perceiving painful stimulus. Thus, the skin is poorly innervated and this allows some surgical procedures to be performed without anaesthesia (castration, incision into the crop).
Hearing and balance receptors are found in the inner ear (vestibulocochlear organ), although the outer ear is not well developed in birds. The opening of the external auditory canal is round and limited by a circular fold. The canal must be kept clean and free from secretions
and the possibility of aural parasites should be considered upon examination.
The middle ear is formed by an elongated
bone (columella) that replaces the auditory ossicles found in mammals.
The inner ear is similar to mammals, but the cochlea is ten times smaller. The sensitivity to resonance is very high, especially in nocturnal birds.
Birds have excellent vision. Eyeballs are very big and situated laterally, so their field of vision is from 280-360º.
The eyeball is flattened (not spherical) and in some species (raptors) quite elongated.
The retina is formed by rods and cones, and has a central fovea formed by cones. 100% of the optic nerve fibers decussate, so the consensual pupil reflex cannot be seen. The pecten is a comb-like structure located within the posterior chamber. It is a pigmented and vascularized membrane, near to the optic nerve entrance, which is floating in the vitreous humor. Its function is to provide nutrition, regulate temperature and sense changes in pressure. Internal ocular muscles are striated, which make the examination of the eye very difficult. In addition to eyelids there is large nictitate membrane (third eyelid) which is very mobile. It protects and lubricates the cornea, aided by the adjacent lacrimal gland.