Do pied tamarins increase scent-marking in response to urban noise?

Sounds produced by human activities are often loud and may mask acoustic signals used by other species for communication. To circumvent this, some animals use various strategies, including shifting modality completely or complementing acoustic information by using additional modalities to communicate. Here we used pied tamarins (Saguinus bicolor) as models to explore whether shifts in communication modalities occur under increased anthropogenic noise or deploy them complementarily. We predicted that in circumstances where noise could impede acoustic communication the study animals would exhibit more scent-marking behaviour (i.e. olfactory communication) while reducing the emission of long calls (i.e. acoustic communication). We collected information on vocal and scent-marking behaviour in nine groups of wild pied tamarins in urban forests in Manaus, Amazonian Brazil. We found that scent marking occurrence increased with noise amplitude, though long call numbers did not change. Thus, our results do not suggest a complete shift between channels but complementation of information, where scent marking may compensate for the impacts of anthropogenic noise on the acoustic channel. This is an interesting result from a conservation perspective as pied tamarins may be capable of coping with city noise to communicate with conspecifics, a key tenet of species survival.