A. Hearing.
1. Birds are most sensitive to sounds with frequencies between 1 and 5 kHz. The upper limit of hearing is about 10 kHz (Brooke and Birkhead, 1991). Humans can hear sounds with frequencies as low as 0.02 kHz and as high as 17 kHz.
B. Eyesight.
1. Vision is a diurnal bird of prey's most important sense for hunting and reacting to danger.
2. Diurnal birds of prey have excellent vision.
a. The eyes are proportionally larger than the eyes of other vertebrates, providing larger and sharper visual images.
b. The retina has more rods and cones (the eye's sensory cells) and is one-half to two times as thick as the retina of other vertebrates. More sensory cells mean better visual acuity.
c. As in humans, the point of sharpest vision is the fovea. Foveae are funnel-like areas of the retina packed with color-perceiving cone cells. Humans have one fovea per eye, while diurnal birds of prey have two.
d. In addition, many diurnal birds of prey have proportionately more sensory cells in the upper half of the retina. This helps a bird perceive images when looking toward the ground from a perch or when flying. As a consequence, to scan the sky, they must turn their heads upside down.
e. Like humans, diurnal birds of prey focus on objects through binocular vision (using two eyes to see); but, can easily detect movement at the edges of their viewing range using just one eye.
3. Diurnal birds of prey are thought to see objects at a distance about the same as or up to three times better than humans. The wedge-tailed eagle (Aquila audax) can discern objects at a distance twice as far as humans. On the other hand, an American kestrel has visual acuity equal to a human's (Martin, 1987).
4. Diurnal birds of prey see color, which may play an important role in food identification and reproductive behavior.
C. Taste.
1. Birds have an acute sense of taste. Taste is used to help avoid harmful foods. Sensory receptors inside the bird's mouth detect sweet, salt, sour (acid), and bitter tastes. Sensitivity to each of these tastes differs from species to species.
D. Smell.
1. The importance of smell differs from species to species. Most diurnal birds of prey aren't sensitive to smell. An exception is the turkey vulture, which is able to locate carrion from the air by smell alone (Brooke and Birkhead, 1991).
E. Tactile.
1. Scientists feel that birds possess a sense of touch much like humans.
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