SUMMARY

The aggressive and defensive behaviour of the ring dove was studied in response to a model predator and to another member of the same species. During a single breeding cycle defensive behaviour increased rapidly just before laying, reached a second peak at the time of hatching, and declined as the squabs became independent. Cocks showed aggressive behaviour to other doves throughout the cycle, but this response reached a peak soon after laying, and declined at the time of hatching.

The effects of seven daily injections of oestrogen, progesterone, progesterone plus oestrogen, testosterone, and prolactin were studied. In both sexes prolactin and progesterone (with and without oestrogen) increased defensive behaviour towards a predator; in hens these hormones also increased defensive behaviour towards other birds. In cocks, however, prolactin had no effect on the response to other doves; progesterone (with and without oestrogen) increased aggressiveness, and oestrogen increased nest-cooing.

Single injections of the same hormones produced similar effects, with the exception that testosterone and oestrogen in hens caused a temporary (1–5 hr.) increase in defensive behaviour. The latency of most hormonal effects was 30 min. to 2 hr., although the injections were intramuscular. This suggests a direct effect on central nervous mechanisms. Progesterone had a latency of 12–18 hr., suggesting an indirect effect.

ABSTRACT

Plasma prolactin began to increase significantly about 5 days after the onset of incubation in both sexes of the dove to reach a peak at the time of hatch. At this time, the concentration of prolactin in the plasma of the female was significantly higher than in the male. In the middle of the incubation period prolactin levels measured over a 24-h period remained constant in both sexes, although the male sits during the middle of the day and the female for the rest of the time. Nest deprivation resulted in a sharp, significant decline in the concentration of prolactin in both sexes. Newly hatched squabs stimulated the release of prolactin only in those doves which had been incubating eggs for several days.

A distinct sex difference was observed in the expression of nest defence behaviour of the ring dove during the breeding cycle. At the time of laying, the female was significantly more aggressive than the male and her aggression increased only slightly up to the time of hatching. In contrast, male aggression increased gradually from a low level at laying to reach a peak at the time of hatching. The levels of plasma progesterone in the female showed a significant increase around the time of lay. No significant changes occurred in the plasma concentration of either progesterone or 17α-hydroxyprogesterone in the male.

Administration of prolactin increased the length of time of incubation of infertile eggs. Nest manipulations which had the effect of inducing the doves to begin incubation 4 days before laying showed that (1) the length of time of incubation of infertile eggs is fixed and independent of events which occur at courtship or oviposition, (2) the initiation of the increase in plasma prolactin concentration during incubation is independent of events which occur at courtship and oviposition and (3) the termination of incubation is always preceded by a fall in the concentration of plasma prolactin.

It is concluded that the length of time of incubation is dependent upon sustained raised levels of plasma prolactin. The concentration of plasma prolactin increases several days after the onset of incubation in response to the tactile stimulation of sitting. High levels, if maintained by visual stimulation from the nest, maintain incubation for a fixed period. After this, if the eggs fail to hatch, prolactin levels fall and the doves cease incubation and begin a new cycle.

J. Endocr. (1986) 110, 447–458

ABSTRACT

Seasonal changes in concentrations of plasma LH, prolactin, thyroxine (T₄), GH and corticosterone were measured in captive male ring doves exposed to natural lighting at latitude 56 °N. Plasma LH levels decreased steeply in autumn when the daylength fell below about 12·5 h but increased in November as the birds became short-day refractory. In comparison with plasma LH concentrations in a group of short-day refractory birds exposed to 6 h light/day from the winter solstice, plasma LH levels in birds exposed to natural lighting increased further in spring after the natural daylength reached about 12·5 h. There were no seasonal changes in plasma prolactin concentrations and plasma T₄ concentrations were at their highest during December, January and February, the coldest months of the year. The seasonal fall in plasma LH levels in September was associated with a transitory increase in plasma T₄, a transitory decrease in plasma corticosterone and a sustained increase in plasma GH.

It is suggested that in the ring dove, short-day refractoriness develops rapidly in November to allow the bird to breed when the opportunity arises, during the winter and early spring. The annual breeding cycle is synchronized by a short-day induced regression of the reproductive system in the autumn, the primary function of which may be to enable the birds to meet the energy requirements for the annual moult. The changes in plasma T₄, corticosterone and especially of GH at this time of year are probably concerned with the control of moult or the associated changes in energy requirements.

J. Endocr. (1986) 108, 385–391