UC Davis

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.