Seasonal variation in preen gland secretions of Tristram's Storm Petrel ( <i>Hydrobates tristrami</i> )

Preen gland secretions are known to vary depending on sex, season and species and are thought to play essential roles in avian life history. However, their chemical composition and functions remain largely unclear in Procellariiform seabirds with well‐developed olfactory senses. Storm petrels, known for their distinctive body odour, may use preen gland secretions as cues for social communication. This study aimed to provide foundational insight into the function of the preen gland in storm petrels by examining the chemical composition and seasonal variation of secretions in male and female Tristram's Storm Petrels Hydrobates tristrami during the breeding season. Qualitative analysis using gas chromatography–mass spectrometry revealed that the major components were lipid esters, particularly octadecyl octanoate, along with hydrocarbons and aliphatic alcohols. The composition showed sex‐specific seasonal variation across breeding stages. While few compounds in females showed significant seasonal variation, a greater number of compounds in males changed significantly from the early breeding period to incubation. Notably, 1‐hexadecanol significantly increased from incubation to chick‐rearing in both sexes. The drivers of these changes remain unclear, whether related to diet, endocrine dynamics or breeding behaviour. Future integrative research, including the monitoring of prey composition and parent–offspring interactions, is needed to clarify these relationships. This study presents the first description of the chemical composition and seasonal variation of preen gland secretions in storm petrels, forming a basis for further investigation into the functional role of the preen gland during the breeding season.