Animals that are small, cryptic, nocturnal and arboreal are difficult to survey with accuracy. The relative neglect of elusive species is partly due to the additional time, money and effort required to undertake successful studies. This is likely to have contributed to the lorisiforms being named the ‘least known of all the primates’ (Nekaris and Bearder, 2011). Prior to the 1990s, few data existed on the distribution and abundance of slender lorises (Loris spp.), leading to their being listed by the IUCN Red List as Least Concern or Data Deficient. The first contemporary surveys of the distribution of Loris led to identification of one new species and the uncovering of low densities that elevated their threat level (Nekaris and Jayewardene, 2004a; Singh et al., 1999, 2000). Abundance estimates found that slender lorises are patchily distributed, even within a single forest reserve, and despite significant survey efforts some forest patches yielded no sightings (Nekaris and Jayewardene, 2004a). The heterogeneous distribution of Loris has been documented (Kumara et al., 2006; Nekaris and Jayewardene, 2004a; Nekaris et al 2013c; Singh et al., 1999). Encounter rates vary by location, habitat and species (2008). While a number of Loris surveys have now been conducted, the sites, survey modes, sampling techniques and data recorded vary across studies; consequently, results are not directly comparable (Table 26.1).