Those working with birds in zoological collections, commercial aviaries and poultry farms have long recognized that the behavior and health of the animals under their care seemed influenced by the quality and amount of light that they received. It many cases, breeding behavior and egg production also seemed linked to light in some way. Observant hobbyists also realize that parrots, canaries, finches and a host of other birds seem to do much better when exposed to natural sunlight. Perhaps you have noticed that birds housed in outdoor exhibits at zoos, or observed in the wild, seem more vigorous, active and brighter in color than individuals of the same species kept indoors?
Details concerning the specific needs of captive birds as regards light quality and quantity are still lacking in some respects, but a great deal has been learned. Much of this information has come as a byproduct of the exploding interest in captive reptiles, many of which fail to thrive if not provided with appropriate lighting regimes.
We now know that most commonly kept bird species rely upon ultraviolet light of a specific type (UVB with a wavelength of 295-310 nanometers) in order to synthesize Vitamin D (if experience with reptiles is any guide, nocturnal species such as owls and nightjars are likely able to obtain adequate amounts of Vitamin D from their diet). Exposure to UVB in this wavelength is also critical to normalization of the calcium/phosphorus ratio. Birds also sense ultraviolet light of another type, commonly known as UVA, as well as the colors red, green and blue (in this regard they are said to have tetrachromatic vision). UVA light provides the aforementioned colors, when viewed by birds, with a certain “tone” that we humans do not sense. Without UVA, birds will not see these colors properly, and their behavior and health will be negatively affected.
Most birds have the number of ways of assessing the quality and duration of the light to which they are exposed, and of conveying that information to the brain. Details concerning light quality are sensed by the retina and relayed to the pituitary gland. The Harderian Gland, locating near the eye, sends information concerning wavelength and photoperiod to the pineal gland. The pineal gland, thyroid gland and hypothalamus use this information to affect the functioning of other organs and of behavior in general. Insufficient or inappropriate levels of UVB or UVA, and daylight periods that are too long or to short, can lead to a host of problems in the functioning of these glands. So, if the quality of the light is not sufficient (i.e. “full spectrum”, or similar to that supplied by natural sunlight), critical glands will malfunction and will, in turn, negatively affect a number of important organs and processes.
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