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ArticleLight and its Role in the Breeding of BirdsPatrick R. Thrush © 1999
When we think of a day, we recognize that this is a 24-hour period. It is quite fixed, as all days are measured by this arrangement. The term daytime is not so fixed. Depending on the season and location, the amount and quality of light available vary tremendously. It is for this reason that when talking about the relationship of animals to light, we refer to these two things as circadian (about a day), and photoperiod (the duration of light in a day).
Of all creatures, birds show us the most dramatic response to changes in photoperiod. The lengthening or shortening of the amount of light in a day triggers migrations, molting, nest-building, and breeding. Much is known about the role of photoperiod in Temperate Zone migratory birds. In our populations of tropical birds, these things are not as clear, as the spectacular process of migration and breeding are not precisely the same as for the migratory flocks.
The information in this article primarily concerns tropical birds. For our purposes, any bird that originates from any location of the world that is between the Tropic of Cancer, and the Tropic of Capricorn (23.5o North and 23.5o South of the Equator) is a tropical bird. Climatologists refer to this band as the Torrid Zone. This is of consideration in providing the most appropriate artificial lighting sources, and other conditions leading to health and breeding.
An understanding of circadian rhythm and photoperiod is of utmost importance for the successful breeder of birds. As much as the timing of the light plays a role, so does the quality of that light. In this article, we will look at the way light affects the health, breeding, and behaviors of the captive bird. In this manner, we can better understand how to apply light to achieve the best results in mate selection, breeding activities, clutch yield, and parent health.
It is important to distinguish that tropical birds do not live in a natural environment that has the same kind of seasonal change in photoperiod as we experience in the Temperate Zone. Differences in daylight period do not often exceed more than one and one-half hours per year. This indicates that other factors exist which affect the seasonal breeding cycle.
Before a discussion of these factors is made, the fact that little variation of photoperiod in the natural environment occurs does not diminish the importance of balanced light, and a proper, regular photoperiod. As noted in our previous discussion, photoperiod is responsible for cuing the endocrine system of birds. If in the case of tropical birds, the photoperiod is diminished, lacking in quality, or irregular, this will affect normal endocrine levels. This will mean that other efforts to successfully breed pairs will suffer. Let us first consider metabolic and physical cycles that are shared by both Temperate and Torrid Zone birds.
In our captive populations of tropical birds, the most reliable status indicator of a bird’s reproductive condition is the feathering cycle. 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. This cycle is shown in Figure 1:
This chart shows approximations for birds in temperate zone areas, above 30 degrees northern latitude. To adjust the chart for natural Torrid Zone conditions, replace the 8/10/14 hour markers with 11/12/13 hour markers. 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.
Rather than attempt to duplicate the intensity or spectral shifts in sunlight that occur throughout the Torrid Zone seasons, we instead modify the length of day to match Temperate Zone changes. Using this system, 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.
One cannot consider all tropical birds equal in terms of response to either photoperiod or environmental changes within the captive environment. As we already know, varying methods and responses depend greatly upon and its natural area of origin. All populations and species may be successfully bred with the right combination of factors interacting with the genetically programmed cycles of the bird.
Aside from the spectral composition of sunlight, the primary trigger to breeding cycles within the tropical population is the climate. This consists of two variables, temperature and humidity. The variation in light that accompanies this is only slightly shorter or longer in period, but there are substantial changes in the quality of the light as the earth moves further away from the sun in the course of the year.
Through its visual apparatus, the bird is able to discriminate these changes. The content of ultraviolet rays, as well as the degree of polarization seen by the bird experiences a change also. Combined with the spectral shift of visible light as the season changes, this provides an additional cue to the endocrine system of the bird that the reproductive organs need to mature or become seasonally dormant. Additionally, the bird’s ability to see into the ultraviolet range allows the distinctive markings necessary for courtship and identification much more predominant when there is greater UV present in the light. This visual capability is the primary method used by birds in selecting and breeding with a mate. Lack of UV may result in a decrease or absence of mating behaviors.
Populations which are more difficult to breed, or that remains dominantly seasonally reversed in their breeding cycle may see greater success in bringing about the breeding cycle, and changing these seasons by modifying the environment of the breeders through temperature and humidity. To accomplish this, two pieces of equipment are required: a humidifier and a heater. Additionally, the breeders must be in an enclosed area that maintains the changes which are being created.
In making these environmental changes, it will become necessary to monitor the conditions. By doing so, it is possible to find the most effective combinations specific to your species, and replicate them successfully later. This monitoring requires a humidity gauge (hygrometer), and a thermometer. These two devices are often found mounted together in a system which also contains a barometer. It is suggested that breeders purchase one of these combination systems.
Changes in barometric pressure have been shown to affect both active breeding behaviors, and the way parents relate to hatchlings. This is particularly pronounced in semitropical areas of the United States, such as Florida. Anecdotal reports relate that sudden changes in pressure increase or decrease nesting patterns, and can also result in parent mutilations of hatchlings. To date no investigation has been done regarding mating rituals, but breeders who monitor barometric pressure will find a correlation for these behaviors when a specific range of conditions has been met. Monitoring these conditions is of utmost importance in recreating conditions which are optimal for breeding within each species.
It is suggested that the photoperiod be increased to 14-16 hours per day, temperature stabilized at 75-80 degrees Fahrenheit, and humidity raised gradually to the 65-75% range. Optimal humidity conditions will be established in each species by observing breeding behaviors. Again, document your conditions for future reference. It may also be of some use in particularly difficult populations to lightly mist the birds with a sprayer several times per day until mating occurs. Do not use ozone generating equipment in a high humidity environment. This results in the creation of acidic residues which coat the environment, including the delicate avian lungs. These kinds of devices are not recommended for any human or bird application, irrespective of manufacturer claims.
There are two primary approaches in using photoperiod to influence breeding behaviors. For our purposes, we will term these gradual change, and sudden change. Both systems will have differing effects on the various species. It should be understood that the gradual system is to be used primarily with breeder pairs who have only one cycle per year. The sudden change system is used to assist with multiple breeding cycles per year, or to modify seasonally conditioned breeding behaviors.
As noted earlier, most tropical species receive an average of 12 hours per day of sunlight. Unlike migratory species, seasonal variation of photoperiod is not a dominant factor in determining breeding cycle and condition. However, the light/endocrine system relationship can still be modified in many tropical species to replicate the physiological conditions manifested by Temperate Zone birds. What we are suggesting here is replacing the normal dominant environmental cue (humidity and temperature) with photoperiod changes.
By far, the standard approach to photoperiod induced breeding is the gradual method. This method involves gradually stepping up the length of the photoperiod from 10-12 hours per day to 14-16 hours per day. Many breeders accomplish this over a two week or more period. After a successful breeding cycle, the light is decreased back to its normal period. It should be noted here that decrease to less than 10 hours per day (i.e., 8 hours) is many times helpful in stopping unwanted or continual egg laying. A great majority of the South American species do well with this method.
Another method with difficult populations, or to induce multiple yearly breeding cycles is the sudden method. Here, the photoperiod is increased to 14-16 hours per day in a single step. It follows that this method may induce behavioral abnormalities such as aggression, increased activity, and improper feathering. However, in populations which have refused to breed under the gradual system, or must be induced to breed twice a year, it is a successful ploy. This writer does not advocate this method, preferring to manipulate other environmental variables instead to achieve breeding. Reduction of photoperiod is the same as in the gradual method. Sudden decrease in photoperiod is also of great use in eliminating unwanted egg-laying. If this system is used, ensure that the hen is receiving ample dietary Vitamin D and Calcium.
This article is by no means meant to be a comprehensive treatise on the relationship of light and environment to breeding. As we have seen, native genetic programming sets wide variables among different species for breeding behaviors. In many species, this process is poorly (if at all) understood. Using the methods discussed here, the breeder is attempting to emulate or replace natural environmental patterns to accomplish the best breeding patterns. It should be obvious for the health of any breeding bird, that the least strenuous methods be employed. However, in difficult populations, this is not always possible.
From this perspective, breeder pair selection should be made from those individual birds which show the greatest adaptation to environmental and light changes. In doing so, we may ensure that the genetic patterns passed down to subsequent breeders are more amenable to conditions experienced in Temperate Zone captive environments. The possibility is also that this type of selection will result in offspring which manifest fewer behavioral problems, and increased resistance to disease. Adaptation to environment always results in decreased stress on the physical and mental process of any animal. At all times remember that breeding quality pet birds is a combination of art and science. Make this philosophy your breeding goal.
All rights reserved. No part of this article may be reproduced in any form or by any means, without written permission from the author.
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Copyright 1999 by Patrick Thrush
