Volatile Compounds in Feathers of the Scarlet Macaw (Ara macao) Reflect Sex and Pair-Bond Status

Birds were traditionally considered to have a limited sense of smell; however, increasing evidence indicates that some taxa, including parrots, possess a functional olfactory system capable of detecting volatile compounds. These chemical cues may convey information related to identity, reproductive status, and mate quality. This study investigates the diversity of volatile compounds in the feathers of scarlet macaws (Ara macao) and examines whether their chemical composition varies according to sex, age, and pair-bond status, as well as whether plumage odor is associated with immune function. Five feathers were collected from the dorsal nape of 18 captive individuals (9 males and 9 females) at Loro Parque Fundación (Tenerife). Volatile compounds were extracted using solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS). Bactericidal plasma activity was assessed via flow cytometry as an indicator of innate immune function. We obtained a significantly higher number and diversity of volatile compounds in males than in females, including greater relative proportions of aldehydes and carboxylic acids and their esters. Meanwhile, partnered individuals showed higher proportions of alkenes and aromatic compounds compared to unpartnered birds. These patterns suggest that plumage volatiles are associated with sex and pair status and may contribute to reproductive communication, potentially facilitating sex recognition and social interactions. No significant relationships were detected between volatile profiles and bactericidal activity or age. Overall, this study expands current knowledge of avian chemical communication in an understudied taxon and highlights the potential relevance of olfactory cues for understanding macaw social biology and welfare.