Biannual complete moult in the black-chested prinia Prinia flavicans

The Black-chested Prinia Prinia flavicans shows two distinctive periods eac h year during which adult birds undergo a complete moult: there is a fast m oult (about 67 days) in spring (September-November) involving all birds sim ultaneously and a slower moult (about 108 days) in autumn (February-June), when about 95% of adults are moulting during April. A biannual complete mou lt pattern was also shown to occur in individual birds. The pattern of seco ndary replacement was variable and unusual for a passerine; the majority re placed S8 to S5/S4 descendantly, or had feathers being renewed ascendantly amongst S4-S7 before the ascendant series starting from the outermost secon dary reached the middle secondaries. The descendant series tended to be lon ger during the autumn moult with S4 most frequently being the last to be re placed in autumn, but S5 last in spring. Breeding was erratic during summer in response to rains and sometimes overlapped extensively with moulting, t he onset of which was less variably timed. When breeding occurred during th e autumn moult, the new plumage was not the usual winter plumage (without t he chest-band), but a new summer plumage.