ENDOGENOUS CIRCANNUAL RHYTHMICITY IN A NON-PASSERINE MIGRANT, THE KNOT CALIDRIS-CANUTUS

We present experimental evidence for endogenous control of circannual rhythms in a long-distance migratory wader, the Knot Calidris canutus. Six individuals of the subspecies canutus were caught during northwar d migration whilst staging in France, and were held together under con stant temperature and photoperiodic conditions (15 degrees C, LD 12:12 ) for 20 months. Rhythms of contour feather and flight feather moult a nd of body mass change persisted throughout the experiment in most bir ds, and showed two cycles over this period. At the beginning of the ex periment the six birds were synchronous, but in the course of the expe riment inter-individual differences in their circannual periods develo ped. Desynchronisation between the rhythms of moult and mass change in the same individual occurred in some birds. The first cycle was delay ed with respect to the natural schedule, while the second cycle had a duration of about a year on average. Since the second cycle was less w ell expressed than the first cycle in most birds, the endogenous rhyth m is likely to be damped rather than self-sustained. The complexity of the annual changes in photoperiod experienced by transequatorial migr ants like Knots calls for more extensive analysis to unravel the natur e of the synchronisation of the endogenous circannual rhythm.