What smells? Developing in-field methods to characterize the chemical composition of wild mammalian scent cues

Olfactory cues play an important role in mammalian biology, but have been challenging to assess in the field. Current methods pose problematic issues with sample storage and transportation, limiting our ability to connect chemical variation in scents with relevant ecological and behavioral contexts. Real-time, in-field analysis via portable gas chromatography-mass spectrometry (GC-MS) has the potential to overcome these issues, but with trade-offs of reduced sensitivity and compound mass range. We field-tested the ability of portable GC-MS to support two representative applications of chemical ecology research with a wild arboreal primate, common marmoset monkeys (Callithrix jacchus). We developed methods to (a) evaluate the chemical composition of marmoset scent marks deposited at feeding sites and (b) characterize the scent profiles of exudates eaten by marmosets. We successfully collected marmoset scent marks across several canopy heights, with the portable GC-MS detecting known components of marmoset glandular secretions and differentiating these from in-field controls. Likewise, variation in the chemical profile of scent marks demonstrated a significant correlation with marmoset feeding behavior, indicating these scents' biological relevance. The portable GC-MS also delineated species-specific olfactory signatures of exudates fed on by marmosets. Despite the trade-offs, portable GC-MS represents a viable option for characterizing olfactory compounds used by wild mammals, yielding biologically relevant data. While the decision to adopt portable GC-MS will likely depend on site- and project-specific needs, our ability to conduct two example applications under relatively challenging field conditions bodes well for the versatility of in-field GC-MS.