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In the canary, the nest-building response of ovariectomized females to exogenous oestrogen is affected both by the length of the photoperiod (Steel & Hinde, 1972) and by male vocalizations (Hinde & Steel, 1976). Gosney & Hinde (1975) showed a similareffect ofphotoperiod on an analagous behaviour in the budgerigar ; oestrogen-treated ovariectomized birds entered the nest-box sooner and spent longer periods within if kept in a long-day than in a short-day photoperiod. In view of the essential role of male vocalizations on reproductive development in the female budgerigar (review by Brockway, 1969) the present paper investigates the effect of male vocalizations on hormone\x=req-\ induced nest-box occupation by ovariectomized female budgerigars. The finding ofGosney & Hinde (1976) that intact females reach a greater degree of reproductive development if exposed to male song during the first half of a 14-h day than during the second half suggests that the sensitivity of the female to male song varies diurnally. The presence of a similar diurnal effect of song on the response to oestrogen is also investigated. Naturally breeding females first enter the nest 8-9 days before the first egg is laid ; just before laying about 60% of time is spent inside, rising to about 90% during incubation. Hutchison (1971) found that oestrogen alone would induce naive ovariectomized females to enter the nest-box. With increasing dose more birds entered and with slightly shorter latencies; 100 μg thrice weekly caused 66% of females to enter within 15 days (median latency 4 days). A combination of oestrogen and prolactin caused all females to enter the nest-box and the time spent inside was comparable to that passed by intact naturally breeding birds. The hormone dosages used here are based on Hutchison's data. The basic procedure for the 4 experiments was similar : details specific to each experiment are given in Table 1. Birds ovariectomized 1-3 months previously were subjected to laparotomy 1 week before experiment and any with residual ovarian tissue were rejected. At the end of each experiment any bird with ovarian tissue weighing >0-l % body weight or with a follicle >1 mm diameter was rejected and does not appear in the analysis. For a week before the experiment birds were housed singly in an 11L:13D photoperiod in cages with a communicating nest box, the entrance of which was blocked. On Day 0 the experimental conditions (14L:10D photoperiod and sound) were introduced, the nest boxes opened and the first injection given. Injections were repeated thriceweekly. Tape recordings of budgerigars and canaries in all-male groups were made on 10-min continuously playing loops. Latency to first nest-box entry was recorded by means of a piece of smoked paper (inspected daily) placed in the base of the nest box; additional data on numbers of birds entering during watches are also given. To estimate the amount of time spent in the nest box groups ofbirds werewatched and recorded as in or out of the nest box at 30 sec intervals. Two-hour watching periods started 2\ or 6^ h after dawn. The results are presented as the percentage of total possible observations in which the bird was in the nest. Mann-Whitney U tests (M.W.U.) were used to assess differences in latency to enter and the percentage of time in the nest box. The Fisher Exact Probability (F.E.) test was used to assess the number of birds entering or not entering. All probabilities are one-tailed. Experiments 1(a) (7 days duration) and 1(b) (14 days duration). The effect of male vocalization on the latency of oestrogen-induced nest-box entry by the female was recorded. Not all birds entered and those that did showed a considerable range of latencies. In both groups the median latency to enter was only slightly less when song was played and in neither was the difference significant.

Effect of male vocalizations on the nest-occupation response of female budgerigars to oestrogen and prolactin