An Introduction To Dragon Biology, 17th Edition, Oxford University Press, 1793 Wrote:One surprising aspect of draconic biology is that there is a limited degree of voluntary control by the female dragon over her reproductive cycle.  While the mating urge itself is hormonal in nature and nigh irresistible when the flock is of sufficient size to reach critical mass, the fact remains that every egg produced by the female is a significant expenditure of energy.  This is both in the immediate sense, in that each egg contains a yolk rich in hydrocarbons, carbohydrates and proteins sufficient to sustain the embryo for the next half year, and in the long term, as the resulting hatchlings will require parental care through to adolescence. 
So while they are hormonally compelled towards mating, female dragons have a crude degree of control over their own fertility, able to choose whether to have none, some, or many eggs in a given year, based on their number of extant pre-adolescent hatchlings, the availability of food, the perceived sense of safety and stability in a given nest, the availability of helpers (and conversely, whether they might be needed to help close kin with their own young) and other such factors. 
Current theories as to the origin of this ability simply point to the fact that pre-modern dragon clutches often had horrifying degrees of hatchling mortality, even with the value that draconic culture placed on parental care, so the ability to suppress the production of closely related competitors would be selected for…