As a Robin Cocks it’s Head

          We spent Christmas with our son and his wife and their family, who live in Arlington, Virginia.  On Christmas Day, the temperature was in the low seventies, with scattered showers throughout the day.  We watched as robins hopped about on their lawn, pausing and cocking their heads to the side while searching for a worm.  Have you ever wondered if the robin is listening for a worm or looking for a worm?  Well, the answer is that the robin cocks its head to focus its eye on the worm; however, at the same time, the bird is also listening for danger lurking nearby.

          According to the Encyclopedia of North American Birds, a bird has two eyelids (folds of skin), one above the eye and one below.  Birds that are active in the daytime draw up the lower lid  when closing their eyes; whereas, birds that are active at night have a more active upper lid when closing their eyes.

          Birds also have a nictitating membrane (aka third eyelid), which can be drawn across the eye from the lower nasal position upward and rearward to moisten and clean the cornea.

          Birds have a highly developed sense of sight.  Man’s vision is about equal to a bird’s sight; however, birds have faster vision, which allows quickness in picking up details.

          Usually, the eyes are the largest part of the bird’s head and often weigh more than the bird’s brain.  The ostrich has the largest eyes of all birds.  When looking at a bird’s eye, one sees only a small part of the eye because the largest part is hidden by the lids and skull.

          The eyes of a bird are fixed in the sockets, which means that  a bird must turn its head and neck to gaze in a different direction.  All birds have monocular (one-eyed) vision, which allows for seeing independently with each eye, and binocular vision, which allows for looking straight ahead.

          Most songbirds have a smaller range of monocular (side) vision and cannot see behind without turning their heads; however, the American woodcock, with its eyes placed toward the top of its head, can see backward, forward, upward and downward at almost 180 degrees with each eye.

          The bittern usually lives among reeds and often escapes notice by standing very still, with its head pointed skyward.  The bittern’s eyes are placed low on the head so that the bird can still look forward binocularly, while maintaining this pose. 

          Birds that feed on small objects, such as seeds and insects, must be able to see them sharply and clearly; therefore, their eyes are rich in cones and adapted to daytime seeing.  Other birds, such as owls that must be able to see at night, have eyes that are rich in rods; however, owls also have enough cones so that they can see sharply during the day.  Birds can see colors as well as man.

          Hearing ranks next to sight in its importance to birds and their survival.  The ear openings of most birds are hidden under feathers at the sides of their heads, just below and in back of the eyes.  The feathers covering the ears do not interfere with a bird’s hearing.  Special feathers in front of the ears are adapted to minimize turbulence in flight and help to protect the hearing organs.  There are no fleshy and cartilaginous outer ears that catch sound waves as in man and other mammals; however, an owl has a moveable skin fold, which is most prominent along the front edge of the ears, that reflects sounds that come to the owl from behind.  Also, in owls, the facial feathers help to detect sounds.

          Owls hear very well because their right and left ears are often  shaped differently, with one ear opening above and one below the owl’s horizontal vision.  An owl’s prey is usually heard before it is seen.  After the owl turns its head so that each ear picks up the same decibels of sound, the owl is then able to see the prey.  The barn owl has the best hearing of all the owls and is able to catch a mouse in complete darkness, using only sounds.

          During WWI, parrots were kept on the Eiffel Tower to give an advance warning of approaching airplanes that were still too far away to be seen by the human eye.  Also, during WWI, it was thought that pheasants and other birds became disturbed by air waves from explosions that were inaudible to the human ear; however, this has since been attributed not to hearing but to a bird’s sensitivity to vibrations.

          Some domestic birds have been used as watchdogs because of their keen hearing.  If you’ve ever tried to sneak up on a flock of geese, you know that it is impossible to do so, even if the whole flock appears to be asleep.  

          Well, it will be a few months before we see robins hopping around in our northern yards in search of worms. Just remember that in the cold and snow of winter there’s a spring that waits to be.