Counts on a communal roost of Blackbirds at Peize (N. Drenthe) during jan-dec 1988, show that the roost was used throughout the year. Peak winter numbers at the roost were 250 in January, followed by a drop to lower summer levels in May (fig. 2). In late summer the use of the roost increased temporary, when moulting juveniles are thought to be comprising most of the roost population (cf. Swann 1975). The winterpopulation was build up in November and reached a maximum of almost 300 Blackbirds in December. There is a strong correlation between the time of arrival at the roost and sunset throughout the year (fig, 3,4). Though the arrival on different conditions of overcast show some influence of light-intensity (fig. 5), differences in median arrival-times are not significant. It is argued that the lack of good roosts or food forces Blackbirds to use the communal roost. This means that the local habitat determines the choice between roosting either solitary or communal.