Study of bird egg predation by the northern pigtailed macaque (Macaca leonina) in the Sakaerat Biosphere Reserve (Thailand) using artificial nests

Abstract

Bird nest predation is frequent and widespread in non-human primates. Yet, very few studies focus on this specific feeding behaviour. Although nest predation is often described as an opportunistic behaviour, little is known on foraging strategies and nest detection in primates. Being the prevalent cause of nest failure, nest predation influences both the population and behavioural ecology of tropical birds, which select specific nest sites and types to reduce detectability and accessibility by predators. Therefore, identifying the nests targeted by the northern pigtailed macaques will help shine light on their foraging strategies. In the degraded and fragmented environment of the Sakaerat Biosphere Reserve, nest predation is high, representing 65% of losses (Khamcha, unpublished data). Snakes are the main predators (33%) while macaques are just behind, accounting for 25% of predation events. Such high predation rates by macaques raises the question as to if nest predation is opportunistic or selective. To determine the nature of this feeding behaviour, we studied, using artificial nests, the influence of several factors on nest predation by macaques: nest type (open-cup versus cavity), microhabitat (i.e., understory density, canopy cover, canopy height, and ground cover), nest density and predated nest density. Furthermore, we explored the relation between ranging patterns, activity budget, diet, and monthly fruit availability on nest predation rates. In our study, macaque predation of artificial nests was high. There was no clear relation between the monthly availability of fruits and predation rates. Nevertheless, the troop’s diet did vary from month to month. Predation rates were higher in the troop’s core area than in the rest of their home range. Additionally, monthly predation rates were negatively correlated with monthly core area size. Our results also indicate that predation rates decreased with nest height but increased with the number of surrounding predated nests, which suggests that, when foraging for eggs, macaques are effective and plunder all the nests set up in the area. The density of nests, nest type, and microhabitat had no effect on predation by macaques. Nest detectability and accessibility did not seem to affect predation by macaques. Therefore, we conclude that nest predation by macaques can be considered as a selective feeding behaviour, with macaques actively searching for this type of rich nutritional food. Bird eggs represent an important part of the macaque’s diet. Consequently, nest predation by this primate might have important implications on the population dynamics of forest-dwelling bird species in the Sakaerat Biosphere Reserve.