Abstract <p>The duration of molt and its different stages in young bramblings and variability under the influence of photoperiodic conditions are considered. The timing and duration of molt season in different places of the distribution area are also investigated, and their determining factors are clarified. The molt process is divided into seven stages. The signs of the stages are the beginning or end of feather replacement in the selected tracts of the feather coat. An analysis of the experimental data revealed the influence of photoperiodic conditions on the duration of the molt of an individual. Under photoperiods corresponding to early molt timing, molt duration averaged 62.0 days, compared to 52.3 days under the conditions of late molt timing. The molt duration is shown to drop as a result of a decrease in the duration of the beginning stages. Data derived from repeated catches in nature confirmed the results of the experiment. A negative relationship was found between the timing of the capture of bramblings and the duration of their intervals between stages 2 and 3 and 3 and 4. A comparison of the duration and timing of the seasons of post-juvenile molt at four different places of the distribution area showed their great geographic variability. The duration of the season is increased in the following sequence: the Lower Ob region (66°40 N, 66°40 E), the White Sea region (67°06 N, 32°41 E), the Middle Ob region (59°58 N, 74°22 E), and the Ladoga region (60°41 N, 32°57 E), amounting to 39, 64, 92, 116 days, respectively. In almost the same sequence, the dates of these seasons reliably shift from early to late. The median catch dates for molting birds are August 24 in the Lower Ob region, August 28 in the White Sea region, September 1 in the Ladoga region, and September 10 in the Middle Ob region. At an early start of the molt season in the Ladoga region (July 2), its end turned out to be one of the latest (October 25), and the duration is twice as long as that of an individual molt. In the Lower Ob, at a late start of the season (August 1), it ends earlier than at other locations of the study area (September 8), and its duration is almost half as long as the molt of an individual. An analysis of the number of birds with different stages and a comparison of the timing of registration of successive stages at each research location with the duration of interstage intervals in molting individuals have allowed us to come to the following conclusion. During the post-juvenile molt season, the Lower Ob region is inhabited mainly by local bramblings with the beginning molt stages. They fly away from this subarctic area before the onset of intense feather replacement. In the study area of the White Sea region, the molt season is dominated by birds that appeared as a result of post-fledging (juvenile) migration. They have middle molt stages. In the Ladoga and Middle Ob regions, both local birds and bramblings from remote territories are recorded. Among the latter, there are birds that live during middle molt stages, but individuals with the last molt stages, which follow in transit during the autumn passage, predominate. This determines the longer duration and the later dates of the molt seasons in the Ladoga and Middle Ob regions.</p>