Influence of oestrogen on the initiation of nesting behaviour in female budgerigars

Intact, breeding female budgerigars enter and occupy a nestbox 8-10 days before egg-laying. Ovariectomized budgerigars did not enter nestboxes. Oestradiol-17 beta monobenzoate (OB) (0-05 mg, i.m.) induced ovariectomized birds to enter nestboxes. Higher dosages (0-1 or 0-5 mg) did not facilitate this effect. The amount of time spent in nesting behaviour by all OB-treated groups did not differ from that shown by a group of intact females during the initial phase of the nesting sequence (first 4 days in the nestbox), but was significantly less than that of intact females undergoing later stages of nesting behaviour (4 days before and after laying the first egg). Oestradiol induced a increase in oviduct weight and size which was dose-dependent. With a low dose (0-05 mg OB), the oviducts were slightly larger than those of intact females which had been in the nestbox 1-2 days. With higher dose levels (0-1-0-5 mg OB), precursor albumen granules had formed in tubular glands of the magnum, a stage more typical of females which had been in the nestbox 4-6 days. The results indicate that low levels of oestrogen induce female budgerigars to enter nestboxes and initiate oviduct development. Subsequent phases of the nesting behaviour and oviduct development may be causally related to other hormones.