In an earlier study of the hormonal initiation of incubation, Lehrman & Wortis (1960) reported that the
occurrence of incubation in response to exogenous progesterone was dependent upon previous breeding
experience. Reproductively experienced male and female doves that had received seven daily 100-µg injections
of progesterone, while in isolation, established incubation within 24 hr of introduction to a nest and eggs,
whereas similarly treated and age-matched reproductively naïve doves did not initiate incubation. Subsequent
study (Bruder & Lehrman 1967) showed that this experience-dependent progesterone-induced incubation was
greatly facilitated, in both males and females by the presence of a similarly treated mate. Left unresolved by
these studies was the question of what exactly is the previous breeding experience that is relevant for progesterone-induced
incubation. That is, before behaving as an experienced bird in that situation, must a dove have
completed an entire reproductive cycle, or have spent some time sitting on eggs, or have only initiated
incubation? The present study examined this question by isolating and identifying those phases of an earlier
cycle which are responsible for a dove's behaving like an expererienced bird when tested for progesteroneinduced
incubation on a later occasion.