Patrick R. Thrush © 1999
In the world of aviculture ideas and practices for providing light to birds abound. Some birdkeepers are fortunate enough to live in temperate climates which allow them to keep their feathered charges outdoors year round. Many pet owners and other hobbyists may not be as lucky (such as apartment dwellers), and are forced to keep their birds inside for part or all of the year.
When this is the situation, allowances must be made for providing ample and proper levels of illumination for your bird. Often times, we may walk into a room that has muted or localized illumination, and it is comfortable for the activities that we are engaged in. But what are the needs of birds that may share these same environments and conditions? To answer this question, we must first look at what role light plays in the life of birds.
Being exoteric (meaning to live in the open) creatures, birds have evolved and established set patterns of daily life. While there are species of bird which are crepuscular (twilight dwelling), and nocturnal (night dwelling), the vast majority of avian species are diurnal (daylight dwelling). This cycle of light to dark is known as the circadian cycle (translated; ‘about a day’), and the sunrise to sunset segment is a photoperiod. Birds have acquired very complex responses to photoperiod in both behaviors and metabolism.
How then, do birds perceive this photoperiod, and by what means can light affect basic issues of metabolism? The answers are both simple and complex. Birds perceive light through two means. First and foremost is through the eye. The retina is capable of transmitting a wealth of information about the intensity, color composition, and polarization (direction) of light. This information travels two directions: to the part of the brain responsible for vision, and through a special pathway to the pituitary gland.
Another important pathway of light is through a special tissue which surrounds parts of the avian eye socket. It is called the Harderian gland, and it is capable of sensing the duration of light which the bird experiences. This information travels onwards to the pineal gland. Taken together, the pineal and pituitary glands act as regulators to much of the endocrine system and process in birds (and other mammal and animal species as well). It is through these mechanisms that the normal circadian clock cycle is adjusted, as well as providing triggers to breeding and migratory behavior.
Now that the reader has survived this basic primer in photozoology, we may begin to discuss what all this means to one who has birds. Once an exoteric animal is separated from its natural environment, it must necessarily default to certain genetically ‘programmed’ routines to help maintain the balance (or homeostasis) of the organism. This is a protective mechanism which has evolved to assist species in surviving when disruptions of the natural native cycle, such as prolonged storms and migration, affect both photoperiod and environment.
This ‘default’ however is intended to serve only on a temporary basis, until such time as normal meteorological conditions are reestablished or the migratory destination has been reached and acclimatization has occurred. In removing birds from their native environments, we have created an unnatural and contrived surroundings which compels the organism to default to programmed biological routines. This form of biological recourse is what explains the fact that species imported from south of the equator may retain their normal breeding seasons and cycles, often for several generations in direct contradiction to the actual photoperiod and season of the environment they now experience.
One may argue at this point that once a new routine has become established
in captive situations, no further thought need be given to emulating a
natural pattern of photoperiod. Nothing could be further from the
truth. Stanley D. Beck in his book, “Animal Photoperiodism”
writes:
“It has been found that many important life functions in both lower animals and man are based on a 24 hour periodicity. The natural 24 hour period of our revolving planet has had profound effects on the organization and functions of living things. For instance, some experimental animals have developed malignant tumors, and others have died from nervous breakdown; these extreme effects occurred because the normal periodicity of internal functions had been seriously disrupted by experimental means” (p. 15).
If then as Dr. Beck and many other scientists indicate, normal photoperiod
plays a crucial role in the welfare of the animal. Combined with
the knowledge that the quality of light also affects the organism, how
is this information to be translated to the benefit of birds and the aviculturist?
Much of what passes as lighting knowledge in aviculture is haphazard and anecdotal at best. Unlike the previous quote of intended disruption through experimental means, many birdkeepers subject their charges to the same types of outcomes through the indiscriminate provision of lighting in various forms. It is for this reason that a scientifically based and consistent method of lighting be employed in all situations where birds do not have open access to natural light, as in outdoor aviaries.
When Dr. John Ott was researching the effects of light on various plants and animals, it became quickly apparent that imbalances in the spectrum of light delivered could affect the organism in a variety of ways. Applying this research to humans, imbalances in lighting have been shown to cause depression, lethargy, decreased immune response, and in some cases, agitation and aggressive behaviors. Each factor noted in the human species has a direct equivalent for animals of all species. Therefore, the application of this principle to birds is that they should also receive balanced illumination, combined with a regulated photoperiod.
Sources of light employed in homes and businesses rarely match, or even attempt to emulate natural sunlight. Incandescent and halogen lighting is heavily loaded in the lower infrared and red spectrum. Cool white and warm white fluorescent devices are loaded primarily into the middle of the spectrum, ranging to one side or another of the visible median of green. Screens, coatings on glass, glass itself, and various plastic window coverings filter light wavelengths very selectively. While the incoming light may appear ‘natural’ to the human observer, birds have a much more finely tuned perceptual range, and the ability to discriminate minor changes in light composition.
Humans and many other animals have trichromatic, or three color vision. Do you know anyone who is color blind? To them, the world appears different than to you or I. Things which we see may not appear to someone with this condition, or appear in an altered form. Birds on the other hand, have tetrachromatic, or four ‘color’ vision. To them, lower wavelength ultraviolet adds another visual perspective to the standard red, blue and green of trichromatic vision. In environments lacking adequate sources of UVA, the effect for birds is much the same as is perceived by those who are color blind. Effort should be made to ensure that whenever possible, a full visual palette is available.
Poultry, gamebird, and other breeders have long known that the degree of spectral saturation affected behavior and offspring sex ratios. Certain afflictions, such as toe picking and feather plucking have responded immediately to the addition of monochromatic red light. Aggressive behaviors and stress related immune weakness can be improved by adjusting the amount of blue light delivered to the subject. One of the great results in applying broad or full spectrum solutions to birds is the increase in endurance, activity, and enhancement of feather condition. Color quality has been demonstrated to be as much an issue as light quantity.
Taken together, all of this information leads to the conclusion that unless one is able to provide a consistent unfiltered source of sunlight to avian areas, supplementation through artificial means becomes a responsible consideration. In assuring that birds have access to a well balanced lighting arrangement that provides consistent periods of light, one is also providing the means that the organism needs to remain in balance. Proper lighting assures the likelihood of a balanced metabolism. This means that the organism makes good use of nutritional intake, and maintains a normal rate of biological function.
While we can never duplicate the benefit of natural environments for birds, we can work to make them as close as possible. By applying quality artificial light sources, a proactive move is in place to achieve balance and consistency in the environment of the bird. It is the responsible action that is called of our stewardship for these wonderful creatures.
REFERENCES
Beck, Stanley D. 1963. Animal Photoperiodism: Relationship of daylength to animal growth, development, and behavior. New York: Holt, Rinehart & Winston.
Ott, John N. 1976. Health and Light. New York: Simon & Schuster.
Copyright 1999 by Patrick Thrush