That Bird Blog – Bird Care and History for Pet Birds

Recent research on avian vision at Sweden’s Lund University has revealed that birds lose their ability to see color at twilight.  These findings have inspired me to consider how we might use lighting in order to improve the health and breeding potential of captive parrots, finches, doves and other birds.

The Findings

The article, published in the Journal of Experimental Biology, points out that birds need 5-20 times the amount of light as do humans in order to see color.  By day, birds have extremely sharp color vision, and see both UVB light and a far greater range of colors than do people.  However, their color vision disappears at twilight – far earlier in the day than does that of any other animal studied thus far.

Light’s Effect on Captive Birds

I believe it is important that we consider the type of light we provide to our birds…the zoos in which I have worked are now experimenting with full spectrum lighting in their bird exhibits.

Poor light quality and intensity may explain the difficulties experienced in breeding otherwise hardy bird species in captivity.  Light can have some unexpected implications for reproduction.  Captive female desert iguanas (lizards native to Southwestern North America), for example, rarely reproduce unless given full-spectrum lighting…without UVB light, they cannot see the pheromone trails laid down by males.

Similar scenarios are likely at work where birds are concerned.  Indeed, there are indications that proper levels of UVA and UVB light encourage natural behaviors, reproduction and strong immune systems in captive birds.

Providing Birds with Appropriate Light

Fortunately, a number of options are open to bird owners.  Exposure to natural sunlight (bearing in mind that glass and plastic filter out UVB rays) is the best of these, but when this is not possible a high quality Full Spectrum Bird Lamp should be utilized.

Further Reading

The new findings on light intensity should be valuable in explaining certain aspects of bird evolution and behavior.  For example, the chicks of Gouldian, firetail and zebra finches, all of which nest in dark tree hollows, sport light-reflecting nodules near their mouths.  To read more about this survival strategy, please see my article Flashy Finch Chicks.

 

Pet keepers have long known that birds react to our own eyes, seeming to be very aware of when we are and are not looking at them.  Researchers at the University of Bristol have now confirmed that birds modify their behavior in accordance with observers’ eye movements (please see “Further Reading” below).

Vision is the most important of the senses for most bird species…the optic lobe of a bird’s brain, and the size of the eyes in relation to the head, are comparatively greater in birds than in mammals.  Today I’d like to pass along some interesting facts on avian eyes.

Location of the Eyes

The eyes of predatory birds such as eagles are set close together at the front of the head, allowing for binocular vision (both eyes focus on the same subject) as in people.

Birds that are hunted by other animals usually have eyes that are set well-off to the sides of the head.  This allows for a greater range of vision and helps them to spot danger.  The ring-necked dove’s field of vision is 300 degrees, and by a slight movement of the head reaches 360 degrees.

Focusing Vision

Birds focus their vision by muscular action which changes the shape of the lens and/or cornea.  The avian eye lens is softer than that of mammals, allowing for quicker focusing.

Visual clarity is also affected by the angle of light as it passes through the eye’s cornea (as well I know – my corneas are pointed, and I’m virtually blind without a covering lens to push them back into shape!).  Cornea angle changes allow penguins to see well under-water, and diving birds such as cormorants to switch quickly from water-based to air-based vision.

Color Vision and Acuity

Structures known as cones and rods affect acuity (clarity) and color vision.  Birds see objects located at the very edge of their field of vision quite clearly – we see only “glimpses” and must turn and focus.  Most see at least 3-4 colors, but more research is needed.

The retinas of some birds have depressed areas, known as foveas, which are supplied with extra cones, allowing for particularly acute vision.  Foveas enable hawks to assess speed and distance while swooping down on prey.  Kingfishers, which dive on fish from above, have two foveas in each eye – one for air acuity and one to help them see when submerged.

Rods are light sensitive, and are particularly abundant in the eyes of nightjars, owls and other nocturnal birds.

Pupils

The eye’s pupil regulates the amount of light that reaches the retina.  Birds change the size of their pupils with highly specialized muscles.  The pupils of bird eyes are thicker than those possessed by most mammals, allowing for greater light penetration and sharper vision.

The Third Eyelid

Birds possess a clear, third eyelid, or nictitating membrane.  This membrane prevents the cornea from drying out during flight and offers protection underwater.

Further Reading

Please see my article European Starlings can Determine When People are Watching  for some interesting research and a personal story about the visual powers of an owl that liked to feed people.