Estimating Primate Densities from Transects in a West African Rain Forest: A Comparison of Techniques

TLDR: In this article, the authors used two line-transect survey techniques and five analytical methods to assess the densities of social groups of seven diurnal primate species resident on Tiwai Island, Sierra Leone, West Africa.

Abstract: (1) We used two line-transect survey techniques and five analytical methods to assess the densities of social groups of seven diurnal primate species resident on Tiwai Island, Sierra Leone, West Africa. (2) A modified standard species-specific strip-width estimation technique was applied to data from twenty-eight single-observer transect samples, each 6 km in length. (3) The second method employed seventeen sweep samples where three observers simultaneously walked parallel transects 100 m apart and 1 km in length. This method used both sightings and localization of vocalizations for density estimation. (4) The third method transformed sighting rates from the single-observer samples into density estimates by incorporating sighting rates and densities from sweep samples into calibration factors. (5) We used long-term data on home-range size and overlap to estimate density for three species for which we had sufficient data. (6) The fifth method employed the hazard-rate model of Hayes & Buckland (1983) which involved transforming estimates of distance to the first sighted individual into estimates of distance to the group centre. (7) The rank orders by species of density estimates produced by all analytical techniques were identical except for the sweep-quadrat method. We found no significant differences among density estimates produced by different analytical methods, except for the C. diana density produced by the sweep samples. (8) We recommend the use of both relatively long single-transect samples and also more localized multi-observer sweep samples. These techniques allow use of a variety of analytical methods.