The tomato anemonefish is one of the larger and more commonly seen members of the genus Amphiprion in Singapore waters, and Entacmaea quadricolor is its primary sea anemone host. In every pair of Amphiprion frenatus, the larger fish with a black body is the female while the bright orange and smaller individual tends to be the male. Entacmaea quadricolor does not always have bubble-tipped tentacles. It has been suggested that individuals hosting fish tend to have bulbous tentacles, while those with unexpanded tentacles are likely to be fishless (see Michael, 2008: 170). Note, however, that the sea anemone featured here hosting a pair of mature fish has both bulbous and unexpanded tentacles.

Habituation allows an observer to closely approach and follow free-ranging animals, as they no longer respond to the observer presence (e.g., through flight, avoidance, display, curiosity). While habituation is implicitly acknowledged as a necessary step before any direct observational studies of primates, there is very little published data on the subject. The aim of this study is to analyse the habituation process over time (17 months) in a wild-feeding troop of northern pigtailed macaques (Macaca leonina) inhabiting a degraded forest fragment of the Sakaerat Biosphere Reserve, Thailand. Based on the number of encounters, contact duration with the studied troop, and behavioural responses to the observer recorded ad libitum and via scan sampling, we found statistical evidence of habituation progress over five stages: early, minimal, partial, advanced, and full. The complete habituation process took nearly 13 months. Factors such as the macaques’ limited experience of human contact, semi-terrestriality, large ranging patterns, fission-fusion dynamics, unpredictable resource use, as well as reduced native fruit availability in this degraded forest fragment may explain the length of the process. It was only possible to collect ranging and behavioural data from the partial habituation stage, although these data were biased toward adult males and sub-adults, while overestimating movement behaviour over inactivity and social behaviours. Our results highlight the importance of analysing behavioural data of fully habituated groups of primates to limit biases of observer presence, and also of not underestimating the habituation process length. This study provides novel information on the habituation process in macaques and proposes an effective methodology to analyse the habituation process across a wide range of primate species.