The induction of nest building in the ring dove (Streptopelia risoria): hormonal and social factors.

Abstract

The reproductive cycle of the ring dove proceeds through several behavioural stages. Courtship is followed by nest building, incubation behaviour, and care of the young. Recent investigations have indicated that the transition from courtship to nest building by the male may be determined in large part by changes in the behaviour of the female. Thus, changes in social factors rather than internal hormonal changes may determine the emergence of nest building by the male. This suggests that courtship and nest building in the male ring dove may share a similar hormonal basis. Male courtship early in the cycle is thought to depend upon the secretion of androgens. However, it has been suggested that oestrogens may play a role in the normal activation of courtship and nest building in the male of this species. The present study was designed to investigate some of the hormonal factors which may be involved in the control of nest building by the male ring dove. Male ring doves were pretested for courtship and nest building, and castrated. A series of daily injection was initiated 21 days after castration and continued for 23 days. Each treatment group included 11 castrated males. SO-treated castrated males received 0.1 cc. sesame oil daily, TP-treated castrated males received 0.2 mg. testosterone propionate in 0.1 cc. sesame oil daily, and OB-treated castrated males received 0.2 mg. oestradiol benzoate in 0.1 cc. sesame oil daily. Posttherapy testing for courtship and nest building was initiated on Day 21 of treatment and continued for 2 days. Testing of males was conducted by pairing them with a diethylstilboestrol- and progesterone-treated female. A third day of testing included an observation for incubation behaviour. After the incubation test, blood samples were obtained from five males in each group for the determination of oestradiol levels by radioimmunoassay. TP- and OB-treated castrated males performed high levels of nest building. In contrast, SO-treated castrated males were deficient in nest building. TP- and OB-treated castrated males selected more reed than pine needles on the first and second days of testing, but the proportion of pine needles chosen increased on the second day. Courtship was also affected by hormone treatment. TP- and OB-treated castrated males, but not SO-treated castrated males, performed high levels of nest soliciting. Only TP-treated castrated males performed bow-cooing. Incubation behaviour was performed by 36% of the TP-treated castrated males and 45% of the OB-treated castrated males, but not by SO-treated castrated males. Females tested with SO-treated castrated males were delayed in occupying the nest site and performed less nest soliciting than females tested with hormone-treated castrated males. The delay of SO-group females in becoming established at the nest site appeared to have been determined by the deficit in nest soliciting in SO-treated castrated males. Oestradiol was found in plasma from OB-treated castrated males but not in plasma from TP- and SO-treated castrated males. These results suggest that the performance of nest building by the male is influenced by secretions from the gonads. Also, earlier reports indicating that courtship and incubation are under gonadal control in the intact male are confirmed. Conversion from testosterone to oestradiol most likely does not account for the similarities in the behaviour of TP- and OB-treated castrated males since oestradiol could not be detected in plasma from TP-treated castrated males. Thus, the stimulation of nest soliciting, nest building and incubation through both oestrogen and androgen treatments in the male ring dove may result from a direct and independent effect of each of these hormones. It is suggested that the neural mechanisms controlling performance of these behaviour patterns may be responsive to both types of sex steroids, although it is probable that androgens alone are responsible for their stimulation in the intact male. Furthermore, the finding that oestradiol did not promote performance of bow-coolng suggests that intra-brain aromatization of androgens to oestrogens may not be a necessary step in the activation of behaviour by androgens.