Many individual researchers have used line transect counts to estimate forest primate abundance. They have devoted less attention to the interpretation of line transect data obtained by several observers, as is often the case in long-term monitoring programs. We present primate relative abundance data that 5 observers collected over 6 yr (not continuous) along 4 different transects each 4 km long in the Mwanihana Forest, Udzungwa Mountains National Park, Tanzania. Total distance walked during transect repetitions is ca. 700 km. The species we saw most frequently was the endemic Udzungwa red colobus Procolobus gordonorum (mean 0.59 groups/km walked), followed by the Angolan black-and-white colobus Colobus angolensis (0.43 groups/km) and Sykes’s monkey Cercopithecus mitis (0.35 groups/km). We sighted the endemic Sanje mangabey Cercocebus galeritus sanjei and the yellow baboon Papio cynocephalus infrequently, the latter being confined to the deciduous forest parts of the transects. We analyzed sighting frequency by gross habitat type, transect, season, and observer. Interobserver differences in the relative abundance of each species were moderate and the few cases of significant variations were due to discordance of only 1 observer from the others. Estimated distances of primate group sightings differ significantly among observers, thus preventing us from deriving estimates of absolute density. Frequency distributions of distance-class intervals are not significantly different among observers, which may indicate gross interobserver consistency in the width of the area sampled. We conclude that unless consistency in data collection is checked, as we did for 2 observers who collected data simultaneously, potential interobserver differences remain an underlying source of variance in the results that cannot be separated from other sources of variance.
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ACKNOWLEDGMENTS
We thank 2 anonymous referees for valuable comments on the manuscript. The Tanzanian Commission for Science and Technology and Tanzanian National Parks Permission granted permission to conduct the study. We thank the wardens and staff of Udzungwa Mountains National Park for their valuable assistance throughout the study. A grant from the Margot Marsh Biodiversity Foundation (MMBF) to C. Ehardt, T. Struhsaker, and T. Butynski provided funds for the study. WWF-Tanzania Program, the University of Georgia Research Foundation, Zoo Atlanta, the Conservation, Food and Health Foundation, and British Airways provided additional funding. F. Rovero also received support through a grant from MMBF to T. Struhsaker and through a Rufford Small Grant; postdoctoral funding from the Provincia Autonoma di Trento to the Museo Tridentino di Scienze Naturali supported his work on data analysis and writing.
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Rovero, F., Struhsaker, T.T., Marshall, A.R. et al. Abundance of Diurnal Primates in Mwanihana Forest, Udzungwa Mountains, Tanzania. Int J Primatol 27, 675–697 (2006). https://doi.org/10.1007/s10764-006-9037-0
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DOI: https://doi.org/10.1007/s10764-006-9037-0