ENDOGENOUS GONADAL, LH AND MOLT RHYTHMS IN TROPICAL STONECHATS - EFFECT OF PAIR BOND ON PERIOD, AMPLITUDE, AND PATTERN OF CIRCANNUAL CYCLES

To investigate the effects of reproduction and associated stimuli on t he circannual cycles of African stonechats Saxicola torquata axillaris birds were held for 29 months in aviaries under a constant equatorial (12.25 h) photoperiod, either singly (10 females and 10 males) or in 10 male/female pairs. The birds of all 3 groups went through circannua l cycles in gonadal size, plasma LH and molt, but groups differed with regard to actual reproductive performance. During the second cycle, o nly one of the singly-held females laid eggs and incubated. In constra st, in the paired females egg-laying and incubation occurred in all bu t one bird. About 50% of the clutches from paired females contained fe rtilized eggs confirming the expectation of behavioral differences bet ween the paired and unpaired birds. However, despite differences in re productive performance there were no differences in either circannual period or duration of reproductive phases. Moreover, there was no corr elation between number of broods produced per season and circannual pa rameters of the paired females. Therefore, the temporal course and, pa rticularly, the period during which reproduction is possible is rigidl y determined by an endogenous program that is not influenced by reprod uctive performance. A rigid program of this kind may be advantageous i n the tropics because it prevents prolongation of the breeding season in years with favourable conditions which in turn could jeopardize opt imal timing of breeding in the following year and thus reduce lifetime reproductive success.