POSTNUPTIAL MOLT VARIATION IN THE WILLOW WARBLER PHYLLOSCOPUS-TROCHILUS IN RELATION TO BREEDING

In a nine-year study of post-nuptial moult interruption in the Willow Warbler, three moult patterns were noted which differed from the norma l pattern. All concerned late-breeding individuals. One pattern was to suspend moult after the first two inner primaries were renewed and re commence at the point of suspension when young had attained independen ce. Another pattern was a very slow renewal of inner primaries with ad jacent feathers only dropped when previous ones were fully grown and s ubsequently proceeding into a full moult when young were independent. In the third pattern, birds commenced their moult at an earlier stage gf the breeding cycle, i.e. before young were independent. In all thre e patterns, post-nuptial moult would be completed earlier than if all birds waited until young achieved independence before moult seas initi ated, as is usually the ease in adults with normal-timed broods.