AUTUMN MOVEMENTS, MOULT AND MEASUREMENTS OF THE LESSER REDPOLL CARDUELIS FLAMMEA CABARET

SUMMARY The annual cycle of Lesser Redpolls breeding in Northumberland is described. Birds return in late April and could rear at least two broods, in the absence of predation, before they begin to moult in early August. The complete moult of both sexes usually begins just after the last brood of young reaches independence. Moult ends in late September and the adults then move southwards immediately. Juveniles also finish their partial moult before they migrate, but those which finish moult well before the adults, apparently wait for the latter before undertaking extensive southward movements, though some disperse over short distances in early September. Some adults and juveniles caught during moult at one site returned to moult there in later autumns, even though they did not breed there. Movement in autumn from Britain to the Continent takes place only at the short sea‐crossings. More recoveries are obtained abroad in years of poor birch seed crop in southern England. Moult of the remiges and rectrices of the adults is described, and its progress recorded by a numerical scoring system whose merits are discussed. The moult score of the primary feathers follows an approximately linear relationship with date, and the moult scores of all individuals of each sex in each year have been used in regression analyses to yield averages of the duration, start and end of moult, an average daily increase of primary moult score, and the spread of the start of moult within each sample of birds. The results are discussed in relation to breeding and migration. The rates of moult of the primaries, secondaries and tail are not independent of each other, though, in contrast to the primaries, the secondary moult score does not increase linearly with date. The average daily increase of primary moult score is closely correlated with the number of primaries growing simultaneously. Each primary took about 16 days to complete growth in each year, but the duration of moult varied between 43 and 56 days in different years. Variation in the timing and duration of moult of Redpolls in Norway, Iceland and Britain is discussed in relation to the breeding season. Plumage sequences of the Lesser Redpoll are reviewed, with emphasis on their application to separation of sex and age classes. Wing lengths of the males and females of a given age overlap considerably, and abrasion alters these lengths only slightly. Older birds have longer wings. Weight changes of adults and juveniles in autumn are examined in detail. Weight variation of individual birds in August and September is more often due to hourly changes in response to feeding than day‐to‐day changes in response to temperature. Weights of adults, but not first‐year birds, decrease at the start but then increase towards the end of the moult, but apparently there is no deposition of fat for migration. Weights of birds caught during their southward movement also show no increase, nor did a group of Lesser Redpolls caught near Oxford in December. It is suggested that day length may be an additional reason for southward migration, besides a reduction in food supply.