Population density estimates of forest duikers (Philantomba monticola & Cephalophus spp.) differ greatly between survey methods

Estimating duiker populations is essential for conservation programmes in Central Africa, but what the most reliable survey method is remains unclear. We estimated forest duiker population densities in Southeast Cameroon using three line‐transect methods: dung counts and diurnal direct observation over 338.2 km, and nocturnal direct observation over 334.7 km. Nocturnal observations resulted in 59.8 and 9.0 individuals km−2 for the blue duiker (Philantomba monticola) and red duikers (Cephalophus callipygus, C. dorsalis, C. leucogaster and C. nigrifrons), respectively, which were much higher than estimates by dung counts and diurnal observation. Only dung counting was applicable for the yellow‐backed duiker (0.8 individuals km−2), due to low encounter rates obtained by the other methods. We argue that nocturnal observation is the most accurate method because the torchlight can pick out duikers' eyes even if the animals are shy and hiding and because multiple counts are unlikely. By contrast, the other methods probably underestimate densities due to poor visibility and reliance on dung production and decay rates calculated in different areas. These results can affect figures used in wildlife management decisions, such as the maximum sustainable yield of game animals, which generally have been based on densities estimated using a single survey method. Résumé Il est essentiel d'estimer l'abondance des populations de céphalophes pour les programmes de conservation en Afrique centrale mais on ne sait pas encore vraiment quelle est la méthode d'étude la plus fiable. Nous avons estimé les densités des populations de céphalophes de forêt au sud‐est du Cameroun en utilisant trois méthodes de transects linéaires : comptage des crottes et observations diurnes directes sur 338,2 km, et observations nocturnes directes sur 334,7 km. Les observations nocturnes ont donné des résultats de 59,8 et 9,0 individus km−2 respectivement pour le céphalophe bleu Philantomba monticola et les céphalophes rouges, à savoir C. de Peters Cephalophus callipygus, C. à bande dorsale noire C. dorsalis, C. à ventre blanc C. leucogaster et C. à front noir C. nigrifrons, qui étaient bien plus élevés que les estimations par comptages de crottes et par observations diurnes. Le comptage des crottes n'était applicable que pour le céphalophe à dos jaune C. silvicultor (0,8 individu km−2) en raison du faible indice kilométrique d'abondance obtenu par les autres méthodes. Nous affirmons que l'observatio