Reproductive Studies of Cockatiels

Abstract

My interest in studying cockatiels stems partly from the vulnerability of this large order of birds (Psittaciformes). For example, of the approximately 145 species of New World parrots, some 55 are threatened. Many of these species are endangered by excessive collection pressure. It is possible that a domestic breeding industry could supply pet birds at a price that would reduce the economic incentive to capture birds from the wild. However, our understanding of the captive breeding management of parrots is too incomplete to make this currently practical.

The University of California's colony of cockatiels was purchased from Aviculture Institute, Newhall, California. Early studies focused on practical questions of nutrition and basic management, e.g. Roudybush et al. (1984); Roudybush and Grau (1986). A management system evolved in which birds were maintained either in flights in a semienclosed aviary or in welded-wire cages (60 x 60 x 30 cm). Breeding was encouraged by attaching to the cages stainless steel nest boxes (30.5 x 20.3 x 30.5 cm) containing sterilized pine shavings. A pelleted diet was provided ad libitum in plexiglass feeders which were designed to minimize spillage. Water was continuously available from nipple drinkers. But reproduction remained problematic. On several occasions nest boxes were attached to cages as a means of encouraging egg production but the response to nest box presentation was low and unduly variable. At best, about 40% of pairs laid eggs. During this period, pairs were used which had been allowed to self-select their mates. Pairing was identified either by co-occupancy of nest boxes in large colony flights, or by "clumping" on perches. The photo-period in early breeding trials was maintained constantly at 14 hr. light: 10 hr. dark (14L:10D), because, inexplicably, preliminary work suggested this species was not influenced by changes in photo-period.

However, in 1984, C.R. Grau, Tom Roudybush and I decided to impose additional environmental cues as a means of stimulating egg production. We reasoned that because cockatiels are desert-dwelling, possibly nomadic, possibly migratory, monogamous, cavity-nesting, and granivorous, they might respond to a combination of changes in photoperiod, light intensity, misting, temperature change and increase in the plane of nutrition (Millam et al. 1988). We, therefore, designed a shotgun like cocktail of environmental cues. Over a period of ten days we increased photo-period from nine to 15 hours of light per day, light intensity from 50-250 lux to 500-1200 lux, and temperature from ambient (approximately 20°C) to 27oc. We likewise increased relative humidity by providing several hours of misting each day and the plane of nutrition by first maintaining birds on millet alone for several weeks, then switching to the pelleted diet, and finally, we provided nest boxes. The birds were already caged with self-selected mates in our standard welded-wire cages, in three decks of 12 cages per deck.

Although this trial was done without a contemporaneous control, the results were very encouraging. Within 21 days of nest box presentation, a period of time we have arbitrarily chosen for comparison purposes, about 90% of pairs were laying eggs. Eggs were removed daily for artificial incubation. Compared to earlier trials, chick hatching weight increased by nearly 1 gram, and clutch length also increased. Some pairs produced eggs every other day for two months until the end of the experiment. (There is little doubt that selection for egg number could radically change the reproductive potential of a flock in just a few generations.)

Our next study (and our first controlled study) simply asked whether nest boxes presented during short days (9L: 150) could elicit as much egg production as nest boxes plus the environmental cocktail. The results provided a clear answer. With 21 days of nest box presentation about 90% of the latter group were producing eggs, while only 17 % in the short day group. The short day group was then exposed to the enhanced environment and egg production increased to expected levels.

We then began testing whether the plane of nutrition contributed anything to the response. Changing from a millet only diet during the short day period to the...