Plasma concentrations of prolactin during incubation and parental feeding throughout repeated breeding cycles in canaries (Serinus canarius).

Concentrations of prolactin were measured in the plasma of male and female canaries serially sampled during repeated breeding cycles. Concentrations in female canaries were low during nest building and increased significantly (P less than 0.05) during the first few days of incubation. Levels increased further (P less than 0.01) in the middle of the incubation period to reach concentrations which were ten times higher than before breeding. Levels remained high for several days after the eggs hatched, as the young were fed in the nest. Prolactin concentrations declined gradually as the young were reared, reaching basal levels by the time the young were fledged, but always increased again in the females as they began incubating eggs in subsequent breeding cycles. Male canaries, which do not incubate but do assist in feeding the young, showed only slight increases in prolactin during the parental period. Male and female canaries which did not breed had low levels of prolactin throughout the experiment. The results show that prolactin secretion is high not only during incubation but also during the parental feeding phase in an altricial passerine bird. These findings are discussed in relation to the different patterns of prolactin secretion which occur during breeding in other birds.