EFFECT OF PHOTOPERIOD ON OESTROGEN- INDUCED NEST-BUILDING IN OVARIECTOMIZED OR REFRACTORY FEMALE CANARIES (SERINUS CANARIUS)

Summary. Nest building was induced in ovariectomized photosensitive canaries with a standard dose of oestradiol (0\m=.\05mg thrice weekly) at various times of year. On a range of daylengths between 6 and 18 hr light/day, building behaviour tended to be more intense if the birds were exposed to long photoperiods. A similar result was found in photorefrac-tory birds, both intact and ovariectomized. Differences in building were unlikely to have been due solely to the amount of time available to birds on different photoperiods as hourly building rates still revealed a difference between groups. A marked differ-ence in the latency of the response to oestrogen was found in the refrac-tory birds. Ovariectomy was not complete in many birds but the evidence from such birds and from the few which had been totally ovariectomized, as well as from those in the refractory period when long days did not result in ovarian growth, showed that endogenous oestrogen secretion was neg-ligible. The effect of long photoperiods in augmenting the induction of nest-building by oestrogen could not be reproduced by injections of either ovine or avian LH. This and other evidence suggests that a direct effect of gonadotrophins is not involved