Chemical communication has been understudied in vertebrates, but no group has been more overlooked than birds, where scent guided behaviors are cryptic, and until recently, olfaction was considered unimportant. It is now well established that birds have a functional sense of smell, yet due to the relative infancy of this field, there is still little known about how chemicals inform the social lives of birds. The overarching objectives of this dissertation were two-fold. First, to increase our understanding of how chemical information aids avian breeding behavior; and second, to develop improved analytical methods for identifying and measuring bird-produced odors, with a focus on the volatile chemicals that may function in communication.With these two objectives in mind, I completed three projects to investigate how chemicals facilitate the reproductive lives of the Leach’s storm-petrel (Oceanodroma leucorhoa). This long-lived, monogamous seabird species is an ideal system for studying avian chemical communication. Leach’s storm-petrels perform their reproductive behaviors under the cover of darkness, but lack good vision in low light conditions, indicating a reliance on non-visual communication. Moreover, they have a large olfactory anatomy, an excellent sense of smell, and a pungent plumage odor. In the first chapter of this dissertation, I used gas-chromatography mass spectrometry to examine the social information present in the strong odor of Leach’s storm-petrels. I discovered that despite interannual variation, the feather chemicals reflected individual identity, which may help storm-petrels maintain their long-term mate bonds. In vertebrates, the immune genes of the Major Histocompatibility Complex (MHC) influence mate choice decisions and enable individual recognition. Moreover, MHC shapes body odor and organisms may use olfaction to evaluate the MHC genotype of conspecifics. In the second chapter of this dissertation, I tested the hypothesis that the plumage chemicals of Leach’s storm-petrels contain information about MHC. This study was motivated by a recent finding that male Leach’s storm-petrels make MHC-based mate choice decisions to select high quality females. I found that feather odors reflected two aspects of MHC genotype: similarity and diversity. These findings were particularly strong for females, which implicates olfaction as a likely mechanism enabling MHC-informed mate choice by males. Making trips to and from their nest is an important behavior that all birds must accomplish to ensure reproductive success. In the final chapter of this dissertation, I investigated how chemicals inform olfactory homing in Leach’s storm-petrels. I analyzed the odors associated with the colony floor, storm-petrel nests, and their avian occupants. I identified gradients of environmental chemicals across the colony, which may aid homing in storm-petrels. Furthermore, I discovered that storm-petrel chemicals are deposited inside the nest, creating unique nest odors that reflect the specific storm-petrel occupants. This is the first evidence of bird nests being scented by the owner’s body odor, which likely facilitates olfactory nest recognition in this species. In summary, the integrative research presented in this dissertation connects the fields of animal behavior, analytical chemistry, and molecular biology to highlight chemicals as an important source of information for breeding birds.

The solubilization and retention of aromas in foods can be improved using phospholipid vesicle dispersions which protect these aromas from evaporation, degradation, and chemical reactions. In this work, a quantification method was developed for the solubilization and retention of volatile aromas in phosphatidylcholine vesicles, with headspace solid phase microextraction (HS–SPME) combined with gas chromatography and mass spectrometry (GC/MS). This method allows us to selectively sample volatile compounds in the vapor phase using a sorbent fiber. HS–SPME is fast, accurate and non-invasive and allows for in situ measurements of partition coefficients for local regions within food products. With this approach, limonene partition coefficients were determined both between vapor and water and between vesicle bilayers and water. The unilamellar, nearly monodisperse vesicles were very effective at solubilizing limonene molecules, with large bilayer–water partition coefficients of ~104 M–1. These values are 3–8 times larger than those observed for short chain phospholipid micelles, which have smaller core volumes. In addition, vesicles can solubilize limonene up to very high mole fractions x_lim≤0.8, where x_lim is the moles of limonene relative to moles of limonene + phospholipid in the bilayers. This maximum solubilization is much greater than that measured for short chain phospholipid micelles (x_lim≤0.5). The bilayer–water partitioning behavior of limonene was investigated as a function of phospholipid composition and vesicle size, using lecithin enriched in phosphatidylcholine and pure dimyristoylphosphatidylcholine (DMPC). There was no significant difference in extent of solubilization whether vesicles were made using DMPC or lecithin, despite the fact that DMPC has saturated 14-carbon fatty acid tails, while lecithin is predominantly unsaturated with 18-carbon fatty acid tails. With an increase in vesicle diameter from ~100 to 200 nm, there was a marginal increase in solubilization for DMPC and a marginal decrease in solubilization for lecithin.The vapor phase concentration of limonene was used to analyze the mixing thermodynamics through calculations of chemical potentials. For a wide range of limonene–lipid mole ratios, constant partition coefficient values could quantitatively capture solubilization in the bilayer, as predicted by ideal–dilute mixing theory for the solute. At high limonene–lipid mole ratios, however, we saw evidence of non-ideal behavior with higher measured lipid–water partition coefficients. Using regular solution theory with an interaction parameter (χ_(PL,L)) of ~1 predicted this partitioning behavior quite well, suggesting that preferential solute–solute interactions may enhance solubilization at higher limonene concentrations. With saturated phospholipids, high mole fractions of limonene in the bilayer lowered the gel–to–fluid lipid phase transition temperature through entropic contributions that could be predicted quite well with freezing point depression theory. Gel, gel/fluid coexistence, and fluid regions were observed over small to large limonene–lipid mole ratios. In the gel/fluid coexistence region, we observed constant vapor phase concentrations of limonene. At low mole fractions of limonene, formation of the gel phase decreased partition coefficients at least two-fold in comparison to the fluid phase. Above the phase transition temperature, decreases in temperature also lowered the partition coefficients, but to a much lower extent. Gel phase partition coefficients were used to modify the freezing point depression model and predict the solubilization behavior of limonene at all compositions at 15 and 20ºC. At these temperatures, experimental data agreed with the theory very well for low total limonene concentrations.