Propithecus verreauxi have been repeatedly censused in parts of the 200-ha reserve at Berenty between 1963 and 1975. Troop rearrangements in 1963 and 1975 showed that both males and females can change troop outside the breeding season. Group sex ratio varies from 0.3 female/male to 5.0 female/male. Usually, at Berenty, groups defend highly exclusive territories, in contrast to ranging patterns elsewhere. In 1980 troops were censused during 2 weeks in November at a different season from earlier studies. They had larger troop feeding dispersion than before, and pairs and triplets of males who travelled apart from bisexual troops. This may be a season of mass male migration, as in Lemur catta, or else a long-term population change. This small reserve should be carefully monitored as its lemurs have so far maintained relative population stability.