Experiments are described whereby the effects of various exogenous reproductive hormones on the brood patch were assessed. It was found that the development of blood vessels is under the control of oestrogen: their rate and degree of development depends on the dose levels employed.
Defeathering is produced by oestrogen plus a secondary hormone. Both progesterone and prolactin are found to act synergistically with oestradiol benzoate and it is not clear which of them is more important under natural conditions. The effects vary with the doses and there is even a suggestion of antagonism when high levels of oestrogen plus prolactin are employed.
Oestrogen causes increase in oviduct weight which can be augmented by both prolactin and progesterone at certain dose levels. With 0·4 mg. oestradiol benzoate thrice weekly neither of these hormones produced any further increase in oviduct weight.
Oestrogen increases nest-building activity. No effect of prolactin or progesterone on nest-building activity or on selection of nest-material was found.