Article
ArticleReprinted from the NCS Journal September/October 1999, Vol. XVI, No. 5The Role of Light in the Healthy Appearance of Caged Birds
by Patrick R. Thrush
In last month’s article (“Lighting and Your Bird”), we discussed the importance and method of providing a regular, balanced source of light for your birds. Many aviculturists are quite surprised to find the wide ranging role that light plays in the life of the bird. In our discussion here, we will examine how light affects the appearance of the captive bird.
The first thought that comes to the mind of most birdkeepers when light is mentioned is Vitamin D production. Many birds are thought to have a unique way of naturally synthesizing this vitamin. In humans, precursor-D (7-dehydrocholesterol) is exposed in the skin to middle range ultraviolet light. In a fully feathered bird, this would be an impossible feat! To get around this covering, most species of bird have a preen (uropygial) gland which is thought to express the precursor-D cholesterol material. Birds spread the substance on their feathers when they preen, and it is exposed to ultraviolet light. When they preen again, they ingest the light synthesized product (previtamin D).
Not all birds have preen glands, and the degree of importance varies among those who do. Professional ornithologists believe that the role of the preen gland can become quite individualized by species. The oils expressed by this gland not only dress out the appearance of feathers, they also help preserve the keratin covering of the beak and scales of the feet. It is this oil which gives some species a strong odor. With the exception of certain macaws and amazon varieties, the bulk of the hookbill and softbill species commonly kept by aviculturists have these glands. In birds where the preen gland is small or absent, specialized feathers break down, providing a powder for the feather dressing.
Preening behaviors are a combination of instinct, biological status (annual cycle, mating patterns, breeding condition, general health, and stress), and visual feather condition. In each of these points, light mediates a physiological and/or behavioral response. Knowing that the rhythm of photoperiod assists in maintaining the natural flow of biological status leads us to also know that deficits in light period or quality will adversely affect natural responses and behavior. It is often noted that when first applying full spectrum (or natural light solutions) feathering quality and appearance improves.
Balanced light and proper photoperiod are critical components of both preening behaviors and the feather health of birds. There are several things that account for this. If a bird is not stimulated through adequate environmental input to maintain proper endocrine function, it will become lethargic and lack endurance for its daily activities, including preening. Preening removes chaff and dander which may adhere to the shafts and barbules of the feathers, making feathering supple and contoured to the body. The bird is the best groomer of its own feather layering. They know when specific feathers need “help” in coming out, and work to spread new and older feathers properly for comfort and insulation.
Negative behaviors may result from inadequate light. When such birds appear ‘bored’, they may resort to feather picking or plucking as an outlet. This kind of behavior is referred to as displacement. When normal activities and responses are diminished because of environmental reasons, a conflict between instinct and physical conditions exists. Displacement of the stress induced on both the nervous and instinctual response to these conflicts may be to pick or pluck. In a later article, we will look at the role of light in both plucking and behaviors.
Feather condition is an indicator of general health as well. Lets then look at the role light plays on the internal functions of the bird with regard to feathering. It has been established that light information affects birds through two different pathways, the pituitary gland through the eye, and the pineal gland through the Harderian gland surrounding the eye. These two glands work together to set the rate of many different metabolic processes. Tied to photoperiod, the natural condition of the bird changes throughout the year. With these changes comes differing stages of molt, appetite, weight, and posture.
The main feathering is molted at least once a year, most often after the end of the breeding season. Many birds will partially molt just before coming into breeding condition. This mini-molt gives them the best possible appearance for courtship and mating rituals. Typically, once a bird has passed the juvenile stage and established its first basic coat, molting follows a very defined pattern: prenuptial molt, nuptial plumage, postnuptial (annual) molt, basic plumage, then repeating the cycle. During each of these times, peak nutritional metabolism works to properly provide the protein and minerals required for the development of keratin, which forms the feathers. Decreased metabolism due to poor light and improper photoperiod will result in less than optimal nutritional absorption, ergo less than optimal new feather growth and condition.
In each of these stages, various hormones are acting to prepare the bird for breeding and other seasonal activities. This process is directly related to photoperiod. As birds move into breeding condition, they gain body weight, and maintain better postures for appeal in the courtship rituals. Weight gain again occurs toward the end dormant season. No bird will be in better feather or form than in the period between the prenuptial and postnuptial molts. This is why natural patterns of photoperiod benefit the appearance and general health of the bird. Extension of these periods may be had by slight manipulations of photoperiod length. Figure 1 shows the relationship of photoperiod to molt.
To duplicate normal rhythms of photoperiod, full spectrum lighting is applied approximately one hour after sunrise, and is turned off an hour before darkness falls. This allows the natural patterns of metabolism and feathering to occur. As mentioned, nuptial feathering can be held for slightly longer periods of time by maintaining a constant time period once into feather. With some birds, problems may occur by remaining in breeding condition for too long. Normal periods may also be shifted to a little earlier or later in the year by this method. Some breeders also are able to achieve two breeding seasons per year via manipulation, but this is not something that contributes to feathering quality or maximum health.
FIGURE 1
The quality of lighting used directly affects how we perceive the coloration of birds. Coloration of feathers themselves is composed of both straightforward reflection, and optical ‘illusions’ which create show and brilliance. Reds, oranges, and yellows are the product of carotene or lipochrome pigments in the feather itself. Dark browns, red browns, and blacks are the result of granules of melanin, similar to the type used in human skin for tanning. Other colors are the result of optical illusions created by the scattering of light. Blue coloration is the result of a thin layer of keratin overlying a melanin pigment. Greens result from adding a carotene yellow layer to the “blue” buildup. Iridescent is what happens when light strikes the feather barbules of multilayered colors.
For all these reflectances and scatterings to occur in their full visual range, a full spectrum of light must be used. This is not only in normal home or aviary situations, it also applies to the showing or exhibition of birds. Variations in lighting sources will cause the same bird to appear quite differently. Incandescent, standard fluorescent, mercury, and halogen light each provide only a part of the spectrum required for proper health and full reflectance. In poorly balanced environments, birds which have quite striking plumage may appear dull and lackluster, both in coat and eye. For best display, full spectrum meets all health requirements, and shows the bird in its best “light”! It is for this reason that organizations which stage competitive showings of birds might consider the possibility of creating full spectrum based lighting standards for displayed birds.
We have seen how the balance of light and regulation of photoperiod affects molting patterns, feather development, feather condition, nutritional use, and general appearance. It cannot be understated that light plays a role in every aspect of the caged bird’s life. By practicing sound lighting management, one is able to assist in creating an environment in which the best feather development and appearance is possible. Whether through artificial full spectrum, or natural sunlight, the only outcome is good!
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Copyright 1999 by Patrick Thrush
