Line transects based on distance sampling methodology were used to census nocturnal raptor species in three different primary lowland forest habitats in the Tambopata region, southeastren Peru. Density estimates were calculated for five owl species in these forest habitats. In general, species were more abundant in primary old floodplain or primary middle/upper floodplain forests than in primary seasonally flooded swamp forest. Density estimates were also higher than those calculated from traditional spot-mapping methods in other lowland forest sites in southeastern Peru and French Guiana. There was no significant difference in the number of individual owls recorded during nights with different cloud cover or during different phases of the moon. Problems of distance estimation at night and unfamiliarity with a range of vocalizations, particularly with Strix owls, may be overcome by conducting a practice period before surveys are undertaken, with transect routes and distance markers adequately set out. Walking transect routes during daylight hours in a practice period also helps to overcome concerns of observer safety.