Increased population density and behavioural flexibility of African clawless otters (Aonyx capensis) in specific anthropogenic environments

Abstract

Land transformation for anthropogenic use is the leading cause of species decline globally. However, few species are able to succeed in anthropogenically disturbed environments. African clawless otters (Aonyx capensis) occur in a wide variety of habitats, and thus are good model species to investigate animal adaptation to anthropogenic environments. Therefore, we aimed to estimate and compare population densities, group size, and activity time of African clawless otters occurring in a transformed area, Millstream Farm, and two natural areas, Verloren Vallei Nature Reserve and Cobham Nature Reserve. Camera trap arrays, consisting of between 18, 27 and 24 cameras, were placed on all three sites, recording otter presence for a total of 2439 camera days. Using random encounter models, we estimated that the transformed area had the highest density of African clawless otters (8.2 ± 2.3 km−2), compared to otter densities at Verloren Vallei and Cobham Nature Reserve, South Africa, (natural areas) with estimated densities of 0.7 ± 0.2 km−2 and 2.1 ± 0.6 km−2 respectively. We found a significant difference (p = 0.007) between group sizes in the transformed area (detections = 112; group size range = 1–5) and natural areas (detections = 29; group size range = 1–3). Furthermore, there was a significant difference in otter activity time (p = 0.033, activity overlap = 66.5 ± 8.33%) between Verloren Vallei Nature Reserve and the transformed area at Millstream Farm. This study illustrates how African Clawless otters exhibit behavioural plasticity in order to exploit a resource-rich anthropogenic environment.