Reproduction in hole-nesting birds, such as cockatiels, is often limited by the availability of nest-sites. This may account for the success cockatiel breeders have in controlling reproductive activity by presenting or withdrawing nest-boxes. For the majority of breeding pairs, a nest-box is essential for egg production, but there are many questions regarding the exact role that the nest-box plays and little is known of how other features of the environment might affect cockatiel reproduction.
Some potential environmental factors that are known to influence the tendency to reproduce in other species include the duration of the light during the day (photoperiod), light intensity, humidity, and plane of nutrition.
Photoperiod and light intensity exert profound effects on the reproductive activity of many species that breed in temperate regions such as California. In fact, the light requirement necessary for stimulating reproduction. in several species is quite well defined, both in terms of minimum light intensity as well as the minimum number of hours of light per day. In some desert-dwelling species, like the zebra finch, an increase in humidity stimulates reproduction. Environmental factors can also augment one another in stimulating reproduction. For example, in turkeys and Japanese quail photostimulated gonadal development (e.g. exposure to a “stimulatory” photoschedule of 14 hr light:10 hr dark [14L:1OD]) is augmented if the ambient temperature is increased from 10C to 25C. As a rule plane of nutrition enhances reproductive performance, but in some species plane of nutrition is the primary initiating stimulus for reproduction. In the crossbill reproduction is stimulated by the availability of particular foodstuffs.
In 1983 we began to investigate whether environmental cues might enhance the reproductive performance of cockatiels. Lacking clues as to which might influence cockatiel reproduction we adopted a “shotgun” approach wherein environmental factors were changed simultaneously.
Thirty-six pairs of cockatiels were housed in wire cages (one pair per cage) in a room with controlled lighting. Temperature was controlled by means of a radiator and an evaporative cooler. Humidity was controlled with the addition of misters.
The birds were first subjected to a 2-3 month period of “winter”-like conditions. Light intensity, photoperiod and ambient temperature were reduced. Misters were turned off and birds were fed a diet of millet. Then, over a period of about two weeks, the winter condition was gradually changed a “spring”-like condition. Light intensity, photoperiod and ambient temperature were increased, a nutritionally complete diet was offered, misters were turned on for several days and then nest-boxes were presented.
The effect on reproductive performance was dramatic. Two trials in which environmental factors were programatically changed can be compared to trials conducted in 1982 and 83 in which birds were housed in the same and fed the same diet but were not exposed to the environmental program described above. Reproductive performance was characterized in four ways: a) percent of all pairs producing eggs within 21 days of nest-box presentation, b) number of eggs produced within 21 days of nest-box presentation, c) Number of eggs laid in succession without a pause of 4 or more days and, d) Number of elapsed days from nest-box presentation to first egg. The results are summarized below.
Measure of Performance Trials_____
1982/83 1984 % change
Percent of pairs producing 31 93 +200
Number of eggs in 21 days 32 152 + 365
Number of eggs in first clutch 3.4 12 + 250
Elapsed days to first egg 14.6 12.5 -20
We observed highly significant increases in percent of pairs producing eggs, number of eggs produced and number of eggs in first clutch (in all trials eggs were collected for artificial incubation the same day they were laid). Elapsed time to first egg was only slightly decreased. These results demonstrate that environmental cues strongly influence reproductive performance in cockatiels.
We are now conducting trials in which each environmental factor is being tested separately in order to determine the exact environmental condition that is sufficient to maximize the reproductive response. It is clear that the nest-box is necessary for permitting breeding in many pairs. But it is now also apparent that the intensity of the resulting reproductive effort is related to the environmental context into which the nest-box is presented. Nonetheless, we are also studying nest-box design to determine which design factors of the box are most effective in providing cues that promote reproductive activity.