Limits to fragmented habitat viability: case study of owl monkeys in a 0.5 ha natural forest island

Our understanding of the viability of primates in anthropogenically fragmented habitats is undermined by the long timeframes for the effects of fragmentation to manifest. Studying primates in natural forest islands can better reveal the limits to habitat viability in the face of fragmentation. We present a study of a group of Azara's owl monkeys (Aotus azarae) occupying a 0.53 ha forest "island", the smallest such forest island and territory ever documented for the genus Aotus. We radio collared one individual and then, for ten months, collected ecological and behavioural data on the island and the group (123 scans, 44 observation days). We also collected forest structure data on the island. While the group did successfully establish itself on the island, the pair did not have an offspring during the birth season. The pair predominantly engaged in resting behaviour in close proximity to each other. Furthermore, the adult male of the group was characterised by eye deformities and bodily injuries, and eventually died nine months after we identified him. These results suggest that, while the forest island may be habitable in the short term, it may not have been sufficient for the long-term survival and reproduction. We propose that this forest island could act as a population sink, where individuals that are not competitive in the highly saturated gallery forest can reside temporarily. Our study shows the importance of considering not only presence/absence, but also behaviour and life history to consider the effects of forest island viability, especially in the face of future scenarios of anthropogenic fragmentation.