Plasma LH and prolactin levels during the reproductive cycle of the cockatiel (Nymphicus hollandicus).

Plasma-luteinizing hormone (LH) and prolactin (Prl) levels were determined using radioimmunoassay during two reproductive cycles in captive cockatiels (Nymphicus hollandicus)--an altricial species in which both parents share incubation and care of young. Birds were stimulated to breed by increasing daylength, light intensity, ambient temperature, and presenting nest boxes. LH levels were elevated during the time of nest inspection in females and peaked during egg laying. In contrast, LH levels were highest in males during nest inspection but were lower during egg laying. In both sexes, LH continued to decline during incubation and care of the young but rose in pairs laying a second clutch. Female and male Prl levels increased during egg laying, peaked during incubation, then declined to egg-laying levels during the nestling stage. Prl continued to decline during the fledgling stage and reached prelaying levels unless a second clutch was begun. In conclusion, in cockatiels, nest inspection and laying are characterized by high LH levels while high Prl levels occur during incubation and feeding of nestlings in both males and females.