The forest-restricted and social crested guineafowl Guttera edouardi is believed to be declining in Afromontane forests due to the fragmentation of its habitat. Incidence functions, derived from presence/absence data from 82 forests, were used to investigate area, isolation and environmental/anthropogenic effects on guineafowl patch occupancy and persistence. The incident probability of the guineafowl increased significantly with increasing area, but was invariant with increasing isolation distance from a putative mainland source patch. Most large patches (>24 ha, mean of occupied patches=192 ha), comprising 22% of those surveyed, were occupied. From incidence functions the estimated minimum viable patch size, at which the extinction probability was unity, was 33 ha. Guineafowl were less likely to be present in forests close (<0.5 km) to human dwellings. Apart from the proximity of a patch to dwellings, all other environmental factors had no significant effect on occupancy patterns. However, because of their large home-range area requirements, the guineafowl are more vulnerable to fragmentation effects, especially area effects, than most forest songbird species. Although reluctant dispersers, crested guineafowl appear to persist in mainland–island metapopulations with low immigration rates. The crested guineafowl is not under immediate threat of regional extinction and current populations are not too isolated to create a sound mainland–island metapopulation network.