AGE AND SEX-DIFFERENCES IN MOLT OF THE MONTAGUS HARRIER

Age and sex differences in the timing and pattern of feather molt in M ontagu's harrier (Circus pygargus) was studied in 184 museum specimens and live birds collected throughout their breeding and wintering rang es. Molt in adults lasted 6-8 mo, starting in May-June in the breeding areas and finishing in January-February on the wintering grounds. App arently, Montasu's harriers do not suspend molt during migration. Molt of primaries started earlier in adult females than in adult males, wh ich was probably related to their different roles in feeding nestlings during the breeding season, but both sexes finished molt at about the same time. Yearlings started body molt on the wintering grounds and t here was a considerable discrepancy in the extent of body molt of year lings between data obtained from skins and those from live birds. Year lings attained plumage similar to that of adults after the first compl ete molt. Timing of flight feather molt in yearlings and second-yr mal es was similar to that of adults even though they were not engaged in reproduction. Nevertheless, they finished molting earlier than older b irds, but this difference was not significant.