Personal odors can play an essential role in communication and individual recognition. Scents make be influenced by genes that are critical for immune function, including genes of the major histocompatibility complex (MHC). This study will marry chemical ecology with modern forensic science techniques establishing the Leach's storm-petrel (Oceanodroma leucorhoa), as a model system studying what appears to be a critical but little studied aspect of social interactions in birds.This long-lived, burrow-nesting species has an excellent sense of smell, making them an ideal model for this investigation. Extensive field study sites have already been established on Bon Portage Island, Nova Scotia, Canada, where over 300 breeding pairs have been genotyped for the MHC class 2B gene. The aim is to characterize the individual odor profiles of these genotyped birds using state-of-the-art chemical techniques developed for human scent discrimination. Specific research objectives are a) to test whether individual birds produce odor signatures related to their MHC-genotype, b) to determine if birds use MHC-related scent marks to label their home burrows, and c) to determine whether the scent of an individual bird is an indicator of individual quality, health and fitness, or plays a role in mate choice decisions. Showing that any species of bird uses MHC-related odors in mate choice decisions would represent a paradigm shift in how biologists think about mate choice decisions in birds, and will provide insights relevant to avian immunology and health in a wide-ranging species. Just as importantly, many species of petrels and albatrosses are facing extinction, and understanding the factors driving mate choice and colony demographics will make a valuable contribution to comprehensive management plans for endangered species. Published phenotypic/chemical or genetic data will be deposited in the Dryad Repository (http://datadryad.org/) or submitted to Genbank (www.ncbi.nlm.nih.gov/genbank/), and deposited in Merritt Data Repository (www.dataone.org/software-tools/merritt-repository-service).