One of 2013’s Bergstrom Award recipients was William Lewis, a Master’s student at the University of Southern Mississippi. Below is a contributed post from William on his research:
My name is William Lewis and a few years ago the Association of Field Ornithologists awarded me the E. Alexander Bergstrom Memorial Research Award to help finance my research examining the gut microbiota of migratory passerines stopping along the northern coast of the Gulf of Mexico. I obtained my Master’s degree from the University of Southern Mississippi in December 2015 and wanted to report on the major findings of my research. The gastrointestinal tracts of vertebrates host a very large and diverse community of microorganisms (the gut microbiota) which has been found to provide many beneficial functions to the hosts such as aiding in digestion and fat metabolism, competitively excluding pathogens, and stimulating the immune system. Very little is known about the gut microbiota of birds, and my research provides the most in-depth characterization of the microbiota of migratory passerines during stopover to date.
I utilized next-generation sequencing to analyze the bacterial communities present in fecal samples (representative of the gut microbiota) collected from 19 Swainson’s Thrushes, 4 Wood Thrushes, and 22 Gray Catbirds. These birds were sampled after crossing the Gulf of Mexico in the spring at a site in coastal Louisiana and before crossing in the fall at a site in coastal Alabama. In general bacterial communities were dominated by two phyla, Proteobacteria and Firmicutes. Bacteria with known beneficial functions, largely Lactobacillus, as well as potentially pathogenic bacteria such as Escherichia and Pseudomonas were identified in all birds sampled. Migrants showed a high degree of inter-individual variation in terms of microbiota composition; this is likely attributable to the fact that birds were sampled mid-way through migration and so likely utilized widely varying habitats and foods before arriving at the sites. No clear differences in microbiota were observed between the different bird species or based on the energetic condition in which migrants arrived at the stopover sites, however fall migrants showed very different microbiota composition compared to spring migrants. This is likely attributable to the differing environments and conditions which the migrants faced in each season, such as broadly different foods available during the two seasons or the influence of crossing the Gulf of Mexico in spring.
Eight birds were re-caught and resampled 1-2 days later during stopover and the microbiota of many of these birds, which was initially highly variable, became more similar to each other. Migrants at the same stopover site are likely exposed to the same habitat and food resources, and it seems that these similar experiences amongst birds caused their microbiota to become more similar throughout stopover. Overall, the results of this research imply that environmental factors are very important for determining the composition of passerine gut microbiota. The first chapter of my Master’s thesis has been accepted to the Journal of Avian Biology and will be published soon (Lewis et al. 2016. “Characterization of the gut microbiota of migratory passerines during stopover along the northern coast of the Gulf of Mexico”). I am in the process of organizing and submitting my second chapter for publication.